Soil Questions

I could use some advice on soil, I use Fox Farm for the most part. I've read a couple places that you should not re-use soil after a grow but me being frugal I wanted to test that theory. I have a hard time believing that soil outdoors and inside my tent are that different. (I certainly don't dig out the soil on my tomato plants and discard). Do outdoor cannabis growers discard soil from their beds? I doubt it......
I'm not arguing I'm right but just questioning and could use some opinions.
With this in mind I mixed my old soil with fresh (maybe 50/50) and I've also started to use Myco+ for root health and will see how it does. What is the concern with re-use? salt build up can be addressed with flushing before re-use and root inoculant and nutes take care of the rest, am I missing something?
Secondly, Can (or should) I also use molasses with Myco+? I understand Myco+ is primarily for Veg growth and molasses s predominantly used in flower. Are there any issues with using both?

There's a reason farmers till their soil well before planting...kills the leftover roots. I grow in small pots so there's not much medium left without string roots.....someone will chirp in with more technical info.

Outdoor soil is more loan silt rock, indoor is soiless peat bark Coco. Indoor soils don't have the breakdown of outside soils and are limedd for a season not life.

If you look after either you can reuse many times but they need the right inputs to stay stable and happy.

Otto D Bonn said:

I could use some advice on soil, I use Fox Farm for the most part. I've read a couple places that you should not re-use soil after a grow but me being frugal I wanted to test that theory. I have a hard time believing that soil outdoors and inside my tent are that different. (I certainly don't dig out the soil on my tomato plants and discard). Do outdoor cannabis growers discard soil from their beds? I doubt it......
I'm not arguing I'm right but just questioning and could use some opinions.
With this in mind I mixed my old soil with fresh (maybe 50/50) and I've also started to use Myco+ for root health and will see how it does. What is the concern with re-use? salt build up can be addressed with flushing before re-use and root inoculant and nutes take care of the rest, am I missing something?
Secondly, Can (or should) I also use molasses with Myco+? I understand Myco+ is primarily for Veg growth and molasses s predominantly used in flower. Are there any issues with using both?

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There is nothing wrong with reusing soil. A lot of people reuse some grow no till and leave roots in and all. Plants draw up a lot of nutrients when growing so the key is to re-amend the soil.

Oldreefer said:

There's a reason farmers till their soil well before planting...kills the leftover roots.

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There's a reason why most conventional big farmers (around here anyway) aren't doing rough fall tillage that much anymore. The main reason is that they'd rather not repeat the mistakes that helped cause the 1930's dustbowl, and are starting to recognize that perhaps science is right and that keeping the soil on your field while increasing organic carbon content in the soil might be a good thing. It seems the only holdouts are the smaller operators that can't afford the cost to modify their planters.

Myco plus molasses is just fine. Thats a good thing in small quanities. The myco can live throughout the whole grow if the conditions are right. Thing is , when the conditions are right for the plant ,the myco is not needed and cannot be of any help but when the plant is missing certain elements in the soil , the myco will help the roots "stretch out" to find more food.

The molasses will help to feed all the bacteria in your soil. It has nothing to do with myco itself. So small amounts of molasses are always good in my opinion.

As for reusing , its the same as when it started just minus a bunch of organic matter. Add back the stuff your plants used and its fine. (its not as simple as it sounds but thats it)

Northwood said:

There's a reason why most conventional big farmers (around here anyway) aren't doing rough fall tillage that much anymore. The main reason is that they'd rather not repeat the mistakes that helped cause the 1930's dustbowl, and are starting to recognize that perhaps science is right and that keeping the soil on your field while increasing organic carbon content in the soil might be a good thing. It seems the only holdouts are the smaller operators that can't afford the cost to modify their planters.

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You need rotation and the right crops, wasn't the dust bowl from constantly planting the same crop.

BBQtoast said:

You need rotation and the right crops, wasn't the dust bowl from constantly planting the same crop.

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I'm sure planting the same crop without rotation wasn't a great thing to do for pest, weed, and nutrient control. But when soil is physically assaulted by regular plowing, the aggregation that keeps it from blowing away is also "blown" away. The disturbance actually causes less year round biological activity. The roots that would otherwise hold onto soil that help limit erosion are destroyed.

It's fine to mistreat soil this way as long as you never a suffer a regional drought. If you do have an abnormally dry period, then all the dust you've made blows away. And around here people got tired of dredging farm soil out of waterways because of spring rains. It's much better to keep the soil on the field.

Then there is the concept of organic carbon and CEC levels. This is why conservation and "no till" help restore long term soil health. There is no sense to pass down your farm to your kids if they can't grow anything in it after you've passed.

Here is Stanford University's take on it: https://www.sciencedaily.com/releases/2019/12/191206132228.htm

Northwood said:

I'm sure planting the same crop without rotation wasn't a great thing to do for pest, weed, and nutrient control. But when soil is physically assaulted by regular plowing, the aggregation that keeps it from blowing away is also "blown" away. The disturbance actually causes less year round biological activity. The roots that would otherwise hold onto soil that help limit erosion are destroyed.

It's fine to mistreat soil this way as long as you never a suffer a regional drought. If you do have an abnormally dry period, then all the dust you've made blows away. And around here people got tired of dredging farm soil out of waterways because of spring rains. It's much better to keep the soil on the field.

Then there is the concept of organic carbon and CEC levels. This is why conservation and "no till" help restore long term soil health. There is no sense to pass down your farm to your kids if they can't grow anything in it after you've passed.

Here is Stanford University's take on it: https://www.sciencedaily.com/releases/2019/12/191206132228.htm

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There is certainly a big move in the UK to conservation tilling at the moment but a lot of the bad stuff really relates to the less developed world. Watching the new plows, they just scoop, seed and replace the divot.

I think another cause of dustbowls is hedge removal and making fields too big, getting much more restrictions back in place here and organic is easier to find and cheaper than it use to be.

The real shame is as we're all overhauling practices the less developed world is slash burning and leaving unusable grassland in its wake.

BBQtoast said:

There is certainly a big move in the UK to conservation tilling at the moment but a lot of the bad stuff really relates to the less developed world. Watching the new plows, they just scoop, seed and replace the divot.

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Those new planters are extremely expensive, but with a couple thousand dollars you can modify the older ones to work with low/no tillage. I used to own a old used John Deere and I replaced the coulter assemblies and the seed-drop discs to fluted, put more weight on it (mine was spring tensioned, not expensive hydraulic) and it worked great for my purposes after a lot of trial-and-error tuning that made me swear a lot over the course of a week. lol

No-till is certainly not an organic thing though. Even on the specialized no-till planters, you have bins for the synthetic fertilizer and stuff. Although I know how controversial this is for a number of reasons, it was Monsanto's Roundup and GMO canola seeds that helped spur the conservation tillage movement in the Canadian Prairies many decades ago and made it easier for that scale of operation. The rapeseed fields there are measured in kilometers and now almost without question are all low/no-till, but obviously not organic! We may be doing other damage with that agriculture practice, but the good news is that the organic carbon content of agricultural soils is now finally increasing: https://www.agr.gc.ca/eng/agriculture-and-the-environment/agricultural-practices/soil-and-land/soil-organic-matter-indicator/

The western world was a couple centuries ahead of the developed world in destroying our soils until just the last few decades. The problem with tropical soils in particular is that there is very little in or on the ground in a natural forest, and that the forest itself makes its own climate. Once the forest is removed, it makes for a shitty place to grow anything, even weeds. I've seen it first-hand in Malaysia/Sarawak, Philippines, and Indonesia (I'm a diver). I've seen jungle before where you wouldn't want your bare skin to touch a leaf, because there would be blood suckers just reaching for you on them as you pass through the dripping wet forest, even in dry season. I've revisited the same places after deforestation and it had turned into an open dry desert. Like WTF?!

You can 100% re-use soil. OP, what kind of grow medium are you using? What kind of nutes are you using? I've been using my own variation of the 3LB mix.

Generally, when using some kind of peat-based growing medium ("soil" for brevity) you have several factors shortening the life of that medium.
- Use of nutrients. If you've been adding dry nutrients to your soil, those will obviously get used up over time so you'll need to re-add. Some people like to use inert media, and liquid ferts, which is why I ask about your setup.
- Peat-based mediums will decay over time. The peat portions, and other organics will start to break down, but the pH will drop too unless you have a proper setup of buffering materials, bacteria, and fungi. For my own setups, I have to re-add dolomite (or lime) every now and then to counter the decaying peat.
- Roots and other leftover hard organic materials should be cleaned out via tools, tilling, hands etc. The extra organic matter decays without adding much to the situation, and can possibly make rooting for new plants slightly more difficult.

Early on in this hobby, I used some pro-mix and miracle grow liquid nutes. After a grow or 2, the amount of salts left behind were getting out of hand. I took all of it, threw it in a big rubbermaid tub, added some fungal andbacterial starter, water, a bunch of organic additives, stirred, then waited. It all turned out well.

MrBaker said:

Roots and other leftover hard organic materials should be cleaned out via tools, tilling, hands etc.

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Considering "hard" organic materials are my plant's sole source of nutrients, I leave the roots of my last grow undisturbed and even recycle the biggest stems and branches by just leaving them on top of the surface of my grow medium. The difference is that I'm doing organic no-till which implies not only soil reuse, but also leaving the soil completely undisturbed from grow-to-grow. I've been experimenting with the method for several years now and tuned the practice as I learned by trial and error. I find it fool-proof for me, which is great considering I can be somewhat of a fool.

Edit: You're right about peat moss breaking down. I had 16" of Pro-mix medium in my grow pot for the first grow, and now after 7 grow cycles it's down to almost 12" of soil. 4" of peat moss gone from 21 square feet of surface area represents a lot of CO2 that was sucked out of my grow tent exhaust! I'm going to have to eventually start topping it up. I plan on doing it gradually so I don't smoother my existing humus layer.

If you are planning on using salts, screening to remove all the roots is really all that is needed to reuse soilless mixes like FF OF and HF. But I still replenish mine with EWC, BG, FBM, and OSM before reuse so I only have to feed them water until I kick them over to flowering! Cannabis / hemp roots are really destructive to soil, they are as bad as tomato, and tobacco plant roots, they suck every usable nutrient out of the environment they are grow in. That's why a lot of commercial hemp, tomato and tobacco farmers will shift their growing areas yearly, or biyearly, and plant sweet clover in last years, or the year before last, growing areas to replenish the soil areas that hemp, tomato and tobacco plants roots have pretty much destroyed! Sweet Clover is known as one of the most incredible naturally soil rebuilding plants in nature.