jondamon
Well-Known Member
Hey everyone,
For those of you that know me and those of you that dont, I may appear to be a master grower but I am far from it and as such i am constantly reading and learning new techniques and methods to help me along my growing journey.
You may remember a thread i posted about Carbs and Amino Acid products and how companies test these products on plants etc.
Here >>>> https://www.rollitup.org/newbie-central/370486-geek-squad-alert-carbohydrates-amino.html <<<<<<
I would now like to post a thread about positive and negative stresses on plants and whether these stresses can actually be good for your plants.
This article was copied out of one of my favourite magazines which i urge you all to look for in your local Hydro Shops. URBAN GARDEN MAGAZINE. See pic .
　
　
　
　
MASTERCLASS POSITIVE STRESS. Can being "unkind" to your plants ever be a good thing? words by Dr Garibaldi
STOP READING THIS!!!!!!! Please make sure you've completely dialed in your grow first. It's far more important! Perfect your daytime and nighttime temps; keep a tight grip on your relative humidity; maintain optimum light levels; exact your feeding regimen, the works - all of it. GET IT RIGHT FIRST.
The techniques described in this article are NOT for beginners and some of this stuff is nothing more than contentious. (hmmm, a sure way to peak your interest though, eh?) We're going to discuss methods of taking your plants to their outer limits and making them go a little crazy in the process. So, if you're coming with us on this journey, buckle up, put on your question hat, and hold on to it tightly! Here we go...............
Personally, i dont care for stress, particularly that special kind imposed by magazine publication deadlines. But i have to admit, one positive effect these deadlines have is to make me work harder!
So what about your plants? We all know that unfavorable growing conditions (eg high temps and low RH) can stress plants out big time. And if these conditions are severe enough, the quality and quantity of your yields will suffer. Invariably badly stressed plants will yield less than plants that have been pampered in every way.
Similar to most things in life, plant stress is not as black and white as you may think. In biology, stress can actually strengthen an orginism. Immunity is obtained only from being subjected to an infection which involves suffering followed by growth, resistance and strength. In the human body a muscle cannot grow without being subjected to stress; a broken bone, when it sets properly, binds stronger than it was before and for that reasonis very unlikely to break a second time at the same juncture. I'm sure many of you will have heard the phrase " what doesnt kill you makes you stronger" or "treat em mean, keep em keen". Well to a certain degree there is some truth to these sayings.
So keep this in mind, is it at all possible that some forms of mild plant stress can actually improve results? The idea that stress can actually be a positive thing may seem alien to some of you. Why would you purposely want to stress plants? Surely stress should be avoided at all costs, right? Well the answer is "yes" and "no". Here we explore the realms of stress; types that should be avoided and other which may well help you to push your plants from being lazy and complacent into relentless and eager producers!
DEFINING PLANT STRESS
There are many factors that will cause plants to become stressed, most of which can be grouped into 2 general categories:
Physical/mechanical stress
Manipulation - bending or training stems, physically damaging the plant
Pruning - removal of leaves, stems, flowers or fruits
Denial - not allowing a certain physical growth factor e.g blocking light, preventing pollination.
Environemental / Abiotic Stress :
Water - Drought, over watering.
Temperature and humidity - Cold (chilling and freezing), heat, wet or dry.
Mineral Deficiency or Toxicity - incorrect fertilisation or salinity.
Pests and diseases.
DANGER STRESSES
Temperature
High heat in your indoor garden can create a myriad of problems. The most common are tall leggy plants with large internodal spacing, small fruits and loose flowers, high water usage, and lower nutrient tolerance. And if temperatures remain high for long periods the stomata will close, plant growth will slow right down and may even cause severe wilting. Low temperatures are less problematic for indoor growers but can occur and cause slow growth and poor nutrient uptake.
HUMIDITY
Low humidity during hot weather is a common problem that should be minitored and avoided. It will cause elevated transpiration and high water usage, increased susceptability over fertilisation, leaf roll, stomata closure, and stunting. Periods of very low humidity can also cause wilting. On the flip side, high humidity will invite fungal infection to take hold and will slow the uptake and transport of water and nutrients.
WATERING / IRRIGATION
Consitantly irrigating the root zone beyond the plants usage capability causes a depletion in oxygen. These anaerobic conditions create poor environment for root growth, cause poor water and nutrient uptake and favour the development of root diseases. A persistant lack of moisture around the rhizosphere can cause wilting, weakend leaf tissue, permanent root damage and nutrient precipitation in the growing media.
LIGHT INTENSITY
Having the grow lights too close will cause localised high heat and low humidity, this will lead to elevated transpiration and may result in permanent leaf tissue damage. NOt having enough light tends to create poor plant growth as low water and nutrient uptake occur. It mist commonly causes elongated stems and large internodal spacing.
pH
All good growers understand the importance of their nutrient solution's pH and keep it within the range 5.5-6.5, thus allowing nutrients to be available for uptake. If the pH swings out of this range for prolonged periods, then nutrients that you plants need will be unavailable or "locked out" which will eventually lead to mineral deficiencies.
NUTRIENT STRENGTH
High nutrient levels can cause permanent damage to your plants. Symptoms include tough leathery foliage, very dark green growth, leaf curl, poor water uptake and leaf tissue necrosis (death). Low nutrient strength is not so damaging but can also create unwanted characteristics such as soft weak stems and leaf tissue, mineral deficiencies, leggy growth and poor fruit and flower development.
PESTS AND DISEASES
Aside from pests physically eating the leaves and causing direct tissue damage, they can also spread disease from plant to plant or make a plant more susceptible to diseases and infections. PLants can usually recover from pest attack if the problem is dealt with quickly but diseases are a little more tricky. Above ground, fungal diseases like Powdery Mildew or botrytis can be controlled once they have infected a plant, but root pathogens, viruses and other forms of invasive diseases are difficult, if not impossible, to shift once they have taken hold.
HEARD ALL THIS BEFORE? OKAY WELL NOW ITS TIME TO INTRODUCE SOME MORE CONCEPTS THAT MAY NOT BE SO FAMILIAR - HOW CAN WE USE STRESS TO OUR ADVANTAGE?
Its good practice to do all you can for your plants during popagation and their early growth stages because keeping plants healthy during this time is crucial for creating healthy vigorous plants. As plants mature and start to produce fruits and flowers, small amounts of stress applied in the right way can actually help to improve a plants favourable characteristics.
Positive stress techniques are often used in commercial horticulture as tools for influencing or 'steering' plants into a growth habut which the grower desires.Steering plants with mild stresses can influence the plant into shifting its efforts rom vegatative growth into fruit or flower production.
VEGATATIVE STEERING
Sometimes you want your plants to grow, sometimes you want them to bloom. MOst growers are familiar with using light cycles to steer photoperiod sensitive plants. But this is just the tip of the iceberg. For most cultivated fast growing plants "mild conditions" play a large role in steering the plant towards a vegatative growth habit. here are some examples.
LOWER NUTRIENT STRENGTHS.
The idea here is that by using a low nutrient strength you make it easy for plants to take up water and nutrients through the roots. Obviously, you need to supply enough nutrients so as not to cause deficiencies or unwanted growth characteristics (stretching/ long internodal distance), so supplying your plants with just above the minimum to reach these requirments makes it easy for the plant, less stressful and therefore helps keep the plant vegatative.
WETTER ROOT ZONES
By regularly replenishing the growing media or root zone with water and nutrients without allowing dry periods to occur, the grower allows the plant easy access to water and nutrients. This helps to steer the plant in a vegatative direction. Its not good practice to purposefully over water the root zone in an attempt to steer vegatatively - all this will do is drive out vital oxygen and impede root function. The aim is to understand your plants (and growing media) water requirments and irrigate just before the growing media starts to dry. To implement this technique, drip irrigation systems offer the most control. The irrigation strategy employed should be short irrigations with a high frequency. These irrigations should supply a little more than the amount the plants are using with only a small amount of runoff occuring. By allowing water and nutrients to be constantly available to the plant it minimises stress and promotes a vegatative growth habit.
　
WARMER ROOT ZONES
Heating the nutrient solution will make it easy for the roots to function and take up water and nutrients. Aiming for 21C (70F) will help even more in steering the plant towards vegatative growth.
　
LOW "DIF" - SMALL DIFFERENCE IN DAY AND NIGHT TEMPERATURES.
The difference between the maximum daytime temperature and the minimum nighttime temperature is often refered to as the "dif", and contributes significantly towards your plants state of growth. By keeping the dif as small as possible the grower stimulates vegatative growth and keeps the plants short and compact. This is a really crucial technique for all indoor growers to get their heads around as shorter plants tend to yield far more under grow lights. Ideally, tokeep plants vegatative and squat you should aim for a dif of no greater than 4C (7F). Time to buy that heater!
　
MILD ENVIRONMENTAL CONDITIONS
To steer plants vegatatively, its important that the environment is as stress free as possible; therefore efficient temperature and humidity control are vital. Stress free growing conditions will be created if plants are able to transpire comfortably and create assimilates (sugars) via photosynthesis effectively. This will be achieved if the air temperature and humidity is within the plants comfort zone, generally 60-70% relative humidity (RH) with the air temperature between 20C-25C (68F-77F) - these conditions should make it comfortable for the plant to function vegatatively.
　
GENERATIVE STEERING
Encouraging plants to flower quickly is a key skill for every indoor grower to acquire. The last thing any of us want are tall, stretching leggy plants that force us to raise up our grow lights. To get the most out of your grow lights indoor gardeners aim for shorter, compact plants with wide canopies - the best way to harness as much of that precious incident light energy as possible. to influence plants speedy shift from vegatative growth into flowering or fruit production (generative growth), most indoor growers cultivating photosensitive plants will alter the light cycle and change out the nutrient solution from a grow forumla to a bloom, and maybe use a few blooming additives through the cycle. This may meet the plants basic requirments to start producing fruit or flowers, but selectively using mild stresses can not only trigger your plants into generative growth more quickly and efficiently, but it can also help focus your plants, throughout the flowering stage, to drive their efforts into producing copious amounts of flowers and fruits. These generative steering tools include:
　
HIGHER NUTRIENT STRENGTHS
By raising the strength of the nutrient solution you are effectively increasing the concentration of mineral salts around the roots. This situation makes it more difficult for the plant to uptake water. when carefully managed, raising the nutrient strength to just below your plants upper tolerance will create a mild stress around the roots and steer the plant towards generative growth. Before undertaking this measure it is important that you know your plants nutrient tolerance. Some species and even different varieties within species will be able to tolerate more nutrient than others. Most importantly, you must have good environmental control to implement this stress technique. If you have problems with low relative humidity or do not have good temperature control, i strongly advise against using high nutrient strength as a steering tool as you will most likely cause problems with over feeding. Only with optimum environmental control can you accomplish generative steering with elevated nutrient strength.
　
DRIER ROOT ZONES
Allowing the growing media to dry slightly between irrigations also causes mild stress. The aim is not to completely restrict the availability of water and certainly not to allow the growing media to dry to a point where the roots are 'worried' that water is running out, but not so much as to allow complete dehydration of the root surface. Implementation of this is fairly simple: during veg you water little and often to stimulate vegatative growth so during flower you water larger volumes less frequently. You dont have to alter the total volume of water given during a day, just the timing of the irrigations. Once again this technique is most controllable with drip irrigation systems.
IRRIGATION START AND STOP TIMES
Aswell as the frequency of the irrigations, the start and stop time can also be used as a steering tool. During the night your plants still use small amounts of water; this creates a drying back of the growing media during the night cycle. The more the growing media dries overnight, the more of a generative action it has. If the growing media is not drying much during the night it may be because you are irrigating too close to the lights turning off, which ismore suited to vegatative growth. Your chosen time to stop and start irrigations will be determined by the growing environment but generally, starting one hour after the lights come on and one hour before they go out will be a good base to start from. If you hand water your plants in veg say one litre each day and you get a small amount of runoff, you could change to watering 2 litres every two days to make your plants more generative.
WORD OF WARNING! if the growing media dries too much and does not receive enough nutrient solution to re saturate it, the nutrient strength in the growing media will start to rise. This will add to steer the plant generatively, but may lead to over fertilisation. Always ensure that during the peak irrigations you supply enough solution to re-saturate the growing media and achieve 10-20% runoff.
COLDER ROOT ZONES
If you have some degree of control over the temperature of the nutrient solution. A drop from 20C (70F) down to 18C (65F) will make it slightly more difficult for the roots to function, but they will still be more than able to take up water and nutrients effectively. This mild root zone stress will not harm growth, it will just nag at the plant to push it in a generative direction.
LARGER DIFFERENCE IN DAY NIGHT TEMPERATURES
Increasing the dif is known to have a positive generative action for most cultivated plants. However, it is not always good for plants that grow large fruits or flowers for the temperature to drop much below 18C(65F) as the transportation of assimilates made during the day can be affected by cold nights. If you have moderate day temperatures 24C(75F) and cannot achieve your desired dif, you may find it beneficial to raise your day temperatures high enough to keep plants growing healthily (26.5C/80F) in order to enable you to increase the daily dif. To steer plants generatively try to aim for a dif of around 8C(15F).
Rapid late evening temperature drops have been used by greenhouse tomato growers for many years as a way of forcing assimilates towards the fruits. A quick fall in air temperature causes the plant to cool down, but the leaves cool much faster than the fruit. This difference in internal temperature causes a draw of photosynthetic assimilates from the large leaves (which have been working hard to make sugars throughout the day) to be translocated to the fruits to advance growth. These quick pre night temperature drops are not so difficult to achieve in an indoor garden because when the grow lights switch off, temperature often drops quickly. As long as the temperature falls enough to quickly cool the leaves, and is then maintained at a reduced level, the fruits or flowers can often stay warmer than the leaves for more than an hour. This is maybe a mild stress technique you are already employing without realising it!
SLIGHTLY HARSH ENVIRONMENTAL CONDITIONS (warmer temps, lower RH)
One of the most severe stresses you can inflict on a plant is environmental stress. High temps coupled with low RH will make it near impossible for most cultivated plants to grow successfully. However, if you have optimal environmental control systems in place, a slight increase in daytime temps combined with a slight decrease in RH can have a significant impact. If for example during vegatative growth you are maintaining the daytime temperature at 24C(75F) with 70% RH , a slight increase for a few hours each day to 26.5C(80F) while maintaining the same RH will increase plant metabolism and transpiration rates for short periods creating small periods of mild stress. During these periods the plant is still fairly comfortable and able to function properly but these slightly harsher conditions steers the plant towards generative growth.
ELEVATED CO2 LEVELS
Higher Co2 levels in the growing environment increases photosynthetic rate. This in turn creates and provides more assimilates to the developing fruits and flowers. This means better fruit and flower initiation and overall more fruit or flowers on the plant which guides the plant in a generative direction. Dosing Co2 early in the light cycle will have a more generative action as this is when peak growth occurs.
　
Crop steering techniques are great tools to have in your arsenal when trying to get the most from your plants. When growing vine (indeterminate) tomato varieties or sweet and chilli peppers you want to harvest fruits for as long as possible. Generative or vegatative steering techniques can be used to balance the plants into a state or constant production, eg not too vegatative and not too generative.
When Growing short cycle plants like bush (determinate) tomato plants or flowering annuals, the goal is to push the plant from vegatative direction and force it into generative state and keep it as generative as possible. This will result in one big flush of fruits or flowers to be harvested in one go. Generative steering techniques are extremely valuable when used in the later stages of a short cycle plants life to help it drive all its efforts into generative production.
OTHER POSITIVE STRESSES.
Topping
Topping is the technique that most growers are familiar with to transform tall skinny plants into a short wide bush. Removing the growing tip reduces 'apical dominance' which is where the central stem is dominant over other side branches. By removing the growing tip early in the plants life many side shoots grow. This helps indoor growers create a more even canopy when growing under lights. Removing the growing tip causes some considerable stress to the plant but creates much more productive and controllable plants in the long run.
Air Pruning
Air pruning roots is another great example of positive stress. It works by allowing the root tip to come into contact with air. During this process the root tip dries back through dehydration. Although this process is fairly stressfull to the root system, it actually enhances it. Once the tip dies it promotes secondary root branching along the length of the root. Once these secondary root tips come into contact with air, they too become air pruned which stimulates more root growth. Much like pinching out the top of the plant to create bushier plants, allowing the root tip to dry creates a more branched root system within the growing media. Air pruning can be done succesfully with rockwool blocks by placing them on a wire rack allowing air to pass underneath them, or with specialised air pruning pots such as 'air pots'.
Thinning
Thinning or a complete clearing of bottom growth is a technique often utilised when growing indoors to concentrate the plants efforts into producing good quality fruits and flowers that are bathed in light. Stems, leaves and flowering sites that are in complete shade will end up producing very little, so removing them may cause some initial stress in the short term but the plant will benefit from more concentrated growth in the long term. Many growers say that the thinning process, when done in the early stages of the flowering cycle helps to speed up the onset of flowers. It may be that the removal of the plant material stresses the plant in a generative direction. Fruit thinning is often carried out when growing cucumbers, peppers and even apples. Removal of some of the smaller fruits helps to divert energy toward the larger fruits and results in better quality large fruits rather than lots of small ones.
　
A final repetitious word of warning.
There's plenty of food for though in this article. And perhaps that the best thing to do. THINK about it. Before we all get instantly carried away with the notion that stress can be good, please read and heed this final word of warning.
PURPOSEFULLY CAUSING PLANT STRESS IN AN ATTEMPT TO IMPROVE RESULTS WILL NOT MASK OTHER GROWING INADEQUACIES SUCH AS POOR ENVIRONMENTAL CONTROL OR NUTRITIONAL DISORDERS!
If you want to have a play with positive stress techniques you should do so in a controlled fashion where all aspects of your grow are completely dialed in . Only then will yo uknow whether what you are doing is positively or negatively affecting your plants. Its one thing to mildly stress a healthy plant, but to stress an already stressed plant could lead to disaster!
　
My god that took forever to write out lol.
Hope the other geeks out there like me enjoyed the read.
　
J
For those of you that know me and those of you that dont, I may appear to be a master grower but I am far from it and as such i am constantly reading and learning new techniques and methods to help me along my growing journey.
You may remember a thread i posted about Carbs and Amino Acid products and how companies test these products on plants etc.
Here >>>> https://www.rollitup.org/newbie-central/370486-geek-squad-alert-carbohydrates-amino.html <<<<<<
I would now like to post a thread about positive and negative stresses on plants and whether these stresses can actually be good for your plants.
This article was copied out of one of my favourite magazines which i urge you all to look for in your local Hydro Shops. URBAN GARDEN MAGAZINE. See pic .
　
　
　
　
MASTERCLASS POSITIVE STRESS. Can being "unkind" to your plants ever be a good thing? words by Dr Garibaldi
STOP READING THIS!!!!!!! Please make sure you've completely dialed in your grow first. It's far more important! Perfect your daytime and nighttime temps; keep a tight grip on your relative humidity; maintain optimum light levels; exact your feeding regimen, the works - all of it. GET IT RIGHT FIRST.
The techniques described in this article are NOT for beginners and some of this stuff is nothing more than contentious. (hmmm, a sure way to peak your interest though, eh?) We're going to discuss methods of taking your plants to their outer limits and making them go a little crazy in the process. So, if you're coming with us on this journey, buckle up, put on your question hat, and hold on to it tightly! Here we go...............
Personally, i dont care for stress, particularly that special kind imposed by magazine publication deadlines. But i have to admit, one positive effect these deadlines have is to make me work harder!
So what about your plants? We all know that unfavorable growing conditions (eg high temps and low RH) can stress plants out big time. And if these conditions are severe enough, the quality and quantity of your yields will suffer. Invariably badly stressed plants will yield less than plants that have been pampered in every way.
Similar to most things in life, plant stress is not as black and white as you may think. In biology, stress can actually strengthen an orginism. Immunity is obtained only from being subjected to an infection which involves suffering followed by growth, resistance and strength. In the human body a muscle cannot grow without being subjected to stress; a broken bone, when it sets properly, binds stronger than it was before and for that reasonis very unlikely to break a second time at the same juncture. I'm sure many of you will have heard the phrase " what doesnt kill you makes you stronger" or "treat em mean, keep em keen". Well to a certain degree there is some truth to these sayings.
So keep this in mind, is it at all possible that some forms of mild plant stress can actually improve results? The idea that stress can actually be a positive thing may seem alien to some of you. Why would you purposely want to stress plants? Surely stress should be avoided at all costs, right? Well the answer is "yes" and "no". Here we explore the realms of stress; types that should be avoided and other which may well help you to push your plants from being lazy and complacent into relentless and eager producers!
DEFINING PLANT STRESS
There are many factors that will cause plants to become stressed, most of which can be grouped into 2 general categories:
Physical/mechanical stress
Manipulation - bending or training stems, physically damaging the plant
Pruning - removal of leaves, stems, flowers or fruits
Denial - not allowing a certain physical growth factor e.g blocking light, preventing pollination.
Environemental / Abiotic Stress :
Water - Drought, over watering.
Temperature and humidity - Cold (chilling and freezing), heat, wet or dry.
Mineral Deficiency or Toxicity - incorrect fertilisation or salinity.
Pests and diseases.
DANGER STRESSES
Temperature
High heat in your indoor garden can create a myriad of problems. The most common are tall leggy plants with large internodal spacing, small fruits and loose flowers, high water usage, and lower nutrient tolerance. And if temperatures remain high for long periods the stomata will close, plant growth will slow right down and may even cause severe wilting. Low temperatures are less problematic for indoor growers but can occur and cause slow growth and poor nutrient uptake.
HUMIDITY
Low humidity during hot weather is a common problem that should be minitored and avoided. It will cause elevated transpiration and high water usage, increased susceptability over fertilisation, leaf roll, stomata closure, and stunting. Periods of very low humidity can also cause wilting. On the flip side, high humidity will invite fungal infection to take hold and will slow the uptake and transport of water and nutrients.
WATERING / IRRIGATION
Consitantly irrigating the root zone beyond the plants usage capability causes a depletion in oxygen. These anaerobic conditions create poor environment for root growth, cause poor water and nutrient uptake and favour the development of root diseases. A persistant lack of moisture around the rhizosphere can cause wilting, weakend leaf tissue, permanent root damage and nutrient precipitation in the growing media.
LIGHT INTENSITY
Having the grow lights too close will cause localised high heat and low humidity, this will lead to elevated transpiration and may result in permanent leaf tissue damage. NOt having enough light tends to create poor plant growth as low water and nutrient uptake occur. It mist commonly causes elongated stems and large internodal spacing.
pH
All good growers understand the importance of their nutrient solution's pH and keep it within the range 5.5-6.5, thus allowing nutrients to be available for uptake. If the pH swings out of this range for prolonged periods, then nutrients that you plants need will be unavailable or "locked out" which will eventually lead to mineral deficiencies.
NUTRIENT STRENGTH
High nutrient levels can cause permanent damage to your plants. Symptoms include tough leathery foliage, very dark green growth, leaf curl, poor water uptake and leaf tissue necrosis (death). Low nutrient strength is not so damaging but can also create unwanted characteristics such as soft weak stems and leaf tissue, mineral deficiencies, leggy growth and poor fruit and flower development.
PESTS AND DISEASES
Aside from pests physically eating the leaves and causing direct tissue damage, they can also spread disease from plant to plant or make a plant more susceptible to diseases and infections. PLants can usually recover from pest attack if the problem is dealt with quickly but diseases are a little more tricky. Above ground, fungal diseases like Powdery Mildew or botrytis can be controlled once they have infected a plant, but root pathogens, viruses and other forms of invasive diseases are difficult, if not impossible, to shift once they have taken hold.
HEARD ALL THIS BEFORE? OKAY WELL NOW ITS TIME TO INTRODUCE SOME MORE CONCEPTS THAT MAY NOT BE SO FAMILIAR - HOW CAN WE USE STRESS TO OUR ADVANTAGE?
Its good practice to do all you can for your plants during popagation and their early growth stages because keeping plants healthy during this time is crucial for creating healthy vigorous plants. As plants mature and start to produce fruits and flowers, small amounts of stress applied in the right way can actually help to improve a plants favourable characteristics.
Positive stress techniques are often used in commercial horticulture as tools for influencing or 'steering' plants into a growth habut which the grower desires.Steering plants with mild stresses can influence the plant into shifting its efforts rom vegatative growth into fruit or flower production.
VEGATATIVE STEERING
Sometimes you want your plants to grow, sometimes you want them to bloom. MOst growers are familiar with using light cycles to steer photoperiod sensitive plants. But this is just the tip of the iceberg. For most cultivated fast growing plants "mild conditions" play a large role in steering the plant towards a vegatative growth habit. here are some examples.
LOWER NUTRIENT STRENGTHS.
The idea here is that by using a low nutrient strength you make it easy for plants to take up water and nutrients through the roots. Obviously, you need to supply enough nutrients so as not to cause deficiencies or unwanted growth characteristics (stretching/ long internodal distance), so supplying your plants with just above the minimum to reach these requirments makes it easy for the plant, less stressful and therefore helps keep the plant vegatative.
WETTER ROOT ZONES
By regularly replenishing the growing media or root zone with water and nutrients without allowing dry periods to occur, the grower allows the plant easy access to water and nutrients. This helps to steer the plant in a vegatative direction. Its not good practice to purposefully over water the root zone in an attempt to steer vegatatively - all this will do is drive out vital oxygen and impede root function. The aim is to understand your plants (and growing media) water requirments and irrigate just before the growing media starts to dry. To implement this technique, drip irrigation systems offer the most control. The irrigation strategy employed should be short irrigations with a high frequency. These irrigations should supply a little more than the amount the plants are using with only a small amount of runoff occuring. By allowing water and nutrients to be constantly available to the plant it minimises stress and promotes a vegatative growth habit.
　
WARMER ROOT ZONES
Heating the nutrient solution will make it easy for the roots to function and take up water and nutrients. Aiming for 21C (70F) will help even more in steering the plant towards vegatative growth.
　
LOW "DIF" - SMALL DIFFERENCE IN DAY AND NIGHT TEMPERATURES.
The difference between the maximum daytime temperature and the minimum nighttime temperature is often refered to as the "dif", and contributes significantly towards your plants state of growth. By keeping the dif as small as possible the grower stimulates vegatative growth and keeps the plants short and compact. This is a really crucial technique for all indoor growers to get their heads around as shorter plants tend to yield far more under grow lights. Ideally, tokeep plants vegatative and squat you should aim for a dif of no greater than 4C (7F). Time to buy that heater!
　
MILD ENVIRONMENTAL CONDITIONS
To steer plants vegatatively, its important that the environment is as stress free as possible; therefore efficient temperature and humidity control are vital. Stress free growing conditions will be created if plants are able to transpire comfortably and create assimilates (sugars) via photosynthesis effectively. This will be achieved if the air temperature and humidity is within the plants comfort zone, generally 60-70% relative humidity (RH) with the air temperature between 20C-25C (68F-77F) - these conditions should make it comfortable for the plant to function vegatatively.
　
GENERATIVE STEERING
Encouraging plants to flower quickly is a key skill for every indoor grower to acquire. The last thing any of us want are tall, stretching leggy plants that force us to raise up our grow lights. To get the most out of your grow lights indoor gardeners aim for shorter, compact plants with wide canopies - the best way to harness as much of that precious incident light energy as possible. to influence plants speedy shift from vegatative growth into flowering or fruit production (generative growth), most indoor growers cultivating photosensitive plants will alter the light cycle and change out the nutrient solution from a grow forumla to a bloom, and maybe use a few blooming additives through the cycle. This may meet the plants basic requirments to start producing fruit or flowers, but selectively using mild stresses can not only trigger your plants into generative growth more quickly and efficiently, but it can also help focus your plants, throughout the flowering stage, to drive their efforts into producing copious amounts of flowers and fruits. These generative steering tools include:
　
HIGHER NUTRIENT STRENGTHS
By raising the strength of the nutrient solution you are effectively increasing the concentration of mineral salts around the roots. This situation makes it more difficult for the plant to uptake water. when carefully managed, raising the nutrient strength to just below your plants upper tolerance will create a mild stress around the roots and steer the plant towards generative growth. Before undertaking this measure it is important that you know your plants nutrient tolerance. Some species and even different varieties within species will be able to tolerate more nutrient than others. Most importantly, you must have good environmental control to implement this stress technique. If you have problems with low relative humidity or do not have good temperature control, i strongly advise against using high nutrient strength as a steering tool as you will most likely cause problems with over feeding. Only with optimum environmental control can you accomplish generative steering with elevated nutrient strength.
　
DRIER ROOT ZONES
Allowing the growing media to dry slightly between irrigations also causes mild stress. The aim is not to completely restrict the availability of water and certainly not to allow the growing media to dry to a point where the roots are 'worried' that water is running out, but not so much as to allow complete dehydration of the root surface. Implementation of this is fairly simple: during veg you water little and often to stimulate vegatative growth so during flower you water larger volumes less frequently. You dont have to alter the total volume of water given during a day, just the timing of the irrigations. Once again this technique is most controllable with drip irrigation systems.
IRRIGATION START AND STOP TIMES
Aswell as the frequency of the irrigations, the start and stop time can also be used as a steering tool. During the night your plants still use small amounts of water; this creates a drying back of the growing media during the night cycle. The more the growing media dries overnight, the more of a generative action it has. If the growing media is not drying much during the night it may be because you are irrigating too close to the lights turning off, which ismore suited to vegatative growth. Your chosen time to stop and start irrigations will be determined by the growing environment but generally, starting one hour after the lights come on and one hour before they go out will be a good base to start from. If you hand water your plants in veg say one litre each day and you get a small amount of runoff, you could change to watering 2 litres every two days to make your plants more generative.
WORD OF WARNING! if the growing media dries too much and does not receive enough nutrient solution to re saturate it, the nutrient strength in the growing media will start to rise. This will add to steer the plant generatively, but may lead to over fertilisation. Always ensure that during the peak irrigations you supply enough solution to re-saturate the growing media and achieve 10-20% runoff.
COLDER ROOT ZONES
If you have some degree of control over the temperature of the nutrient solution. A drop from 20C (70F) down to 18C (65F) will make it slightly more difficult for the roots to function, but they will still be more than able to take up water and nutrients effectively. This mild root zone stress will not harm growth, it will just nag at the plant to push it in a generative direction.
LARGER DIFFERENCE IN DAY NIGHT TEMPERATURES
Increasing the dif is known to have a positive generative action for most cultivated plants. However, it is not always good for plants that grow large fruits or flowers for the temperature to drop much below 18C(65F) as the transportation of assimilates made during the day can be affected by cold nights. If you have moderate day temperatures 24C(75F) and cannot achieve your desired dif, you may find it beneficial to raise your day temperatures high enough to keep plants growing healthily (26.5C/80F) in order to enable you to increase the daily dif. To steer plants generatively try to aim for a dif of around 8C(15F).
Rapid late evening temperature drops have been used by greenhouse tomato growers for many years as a way of forcing assimilates towards the fruits. A quick fall in air temperature causes the plant to cool down, but the leaves cool much faster than the fruit. This difference in internal temperature causes a draw of photosynthetic assimilates from the large leaves (which have been working hard to make sugars throughout the day) to be translocated to the fruits to advance growth. These quick pre night temperature drops are not so difficult to achieve in an indoor garden because when the grow lights switch off, temperature often drops quickly. As long as the temperature falls enough to quickly cool the leaves, and is then maintained at a reduced level, the fruits or flowers can often stay warmer than the leaves for more than an hour. This is maybe a mild stress technique you are already employing without realising it!
SLIGHTLY HARSH ENVIRONMENTAL CONDITIONS (warmer temps, lower RH)
One of the most severe stresses you can inflict on a plant is environmental stress. High temps coupled with low RH will make it near impossible for most cultivated plants to grow successfully. However, if you have optimal environmental control systems in place, a slight increase in daytime temps combined with a slight decrease in RH can have a significant impact. If for example during vegatative growth you are maintaining the daytime temperature at 24C(75F) with 70% RH , a slight increase for a few hours each day to 26.5C(80F) while maintaining the same RH will increase plant metabolism and transpiration rates for short periods creating small periods of mild stress. During these periods the plant is still fairly comfortable and able to function properly but these slightly harsher conditions steers the plant towards generative growth.
ELEVATED CO2 LEVELS
Higher Co2 levels in the growing environment increases photosynthetic rate. This in turn creates and provides more assimilates to the developing fruits and flowers. This means better fruit and flower initiation and overall more fruit or flowers on the plant which guides the plant in a generative direction. Dosing Co2 early in the light cycle will have a more generative action as this is when peak growth occurs.
　
Crop steering techniques are great tools to have in your arsenal when trying to get the most from your plants. When growing vine (indeterminate) tomato varieties or sweet and chilli peppers you want to harvest fruits for as long as possible. Generative or vegatative steering techniques can be used to balance the plants into a state or constant production, eg not too vegatative and not too generative.
When Growing short cycle plants like bush (determinate) tomato plants or flowering annuals, the goal is to push the plant from vegatative direction and force it into generative state and keep it as generative as possible. This will result in one big flush of fruits or flowers to be harvested in one go. Generative steering techniques are extremely valuable when used in the later stages of a short cycle plants life to help it drive all its efforts into generative production.
OTHER POSITIVE STRESSES.
Topping
Topping is the technique that most growers are familiar with to transform tall skinny plants into a short wide bush. Removing the growing tip reduces 'apical dominance' which is where the central stem is dominant over other side branches. By removing the growing tip early in the plants life many side shoots grow. This helps indoor growers create a more even canopy when growing under lights. Removing the growing tip causes some considerable stress to the plant but creates much more productive and controllable plants in the long run.
Air Pruning
Air pruning roots is another great example of positive stress. It works by allowing the root tip to come into contact with air. During this process the root tip dries back through dehydration. Although this process is fairly stressfull to the root system, it actually enhances it. Once the tip dies it promotes secondary root branching along the length of the root. Once these secondary root tips come into contact with air, they too become air pruned which stimulates more root growth. Much like pinching out the top of the plant to create bushier plants, allowing the root tip to dry creates a more branched root system within the growing media. Air pruning can be done succesfully with rockwool blocks by placing them on a wire rack allowing air to pass underneath them, or with specialised air pruning pots such as 'air pots'.
Thinning
Thinning or a complete clearing of bottom growth is a technique often utilised when growing indoors to concentrate the plants efforts into producing good quality fruits and flowers that are bathed in light. Stems, leaves and flowering sites that are in complete shade will end up producing very little, so removing them may cause some initial stress in the short term but the plant will benefit from more concentrated growth in the long term. Many growers say that the thinning process, when done in the early stages of the flowering cycle helps to speed up the onset of flowers. It may be that the removal of the plant material stresses the plant in a generative direction. Fruit thinning is often carried out when growing cucumbers, peppers and even apples. Removal of some of the smaller fruits helps to divert energy toward the larger fruits and results in better quality large fruits rather than lots of small ones.
　
A final repetitious word of warning.
There's plenty of food for though in this article. And perhaps that the best thing to do. THINK about it. Before we all get instantly carried away with the notion that stress can be good, please read and heed this final word of warning.
PURPOSEFULLY CAUSING PLANT STRESS IN AN ATTEMPT TO IMPROVE RESULTS WILL NOT MASK OTHER GROWING INADEQUACIES SUCH AS POOR ENVIRONMENTAL CONTROL OR NUTRITIONAL DISORDERS!
If you want to have a play with positive stress techniques you should do so in a controlled fashion where all aspects of your grow are completely dialed in . Only then will yo uknow whether what you are doing is positively or negatively affecting your plants. Its one thing to mildly stress a healthy plant, but to stress an already stressed plant could lead to disaster!
　
My god that took forever to write out lol.
Hope the other geeks out there like me enjoyed the read.
　
J
