Have you ever run a TDS test on your water with a quality meter that's been correctly calibrated?
Looking for a mail in soil test
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growerNshower
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No quality meter here, but measured tap with a cheap TDS meter and it read 25-30 ppm. Distilled water measured 0 ppm.
To "calibrate" I prepared a solution of salt in distilled water (1 g in 250 ml water). All I had was sea salt, but should be mostly sodium chloride. I then did a serial 2-fold dilution and measured each dilution with my cheap TDS meter (see column D of table). I looked up ppm of NaCl solution from a random website and it seems fairly close, at least at higher concentrations (column E). I tried to calculate ppm myself, but I'm off by about a factor of 2....not sure what I did wrong, but calcs below table in image.
Nonetheless, how can I use this to improve my soil/water?
Thanks!
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Right on! Applied science in an effort to realize informed understanding. Such a rarity here...
Unfortunately, making a sodium chloride solution is not an effective means for calibrating a TDS meter. Solution concentrations vary greatly dependent on the temperature of the solvent. In this case, the higher the solvent temperature, the more dissolved sodium chloride it can carry. The inverse is also true. If your meter was meant to be calibrated, it would have come with a calibrating solution. I'm pretty sure that this is applicable only to meters designed to test TDS solutions expected to be over ~1000 ppm.
There are some major differences in utilizing soil tests meant for agriculture and applying them to potted container gardening...
Like most agricultural crops, the majority of cannabis plant roots that adsorb nutrients grow laterally, away from the main stalk, not down, and reside within the top 6-8 inches of soil.
For ease of understanding, let's assume an in-ground planting where the lateral expansion of the root structure goes as far as the edge of the plant's branches, and no further (I expect it's much further). And let's also assume a three foot wide plant. The nutrient adsorbing roots of this plant would occupy a volume of soil roughly equal to 4.66 cubic feet of soil (3.14 x 1.5 square feet x .66 ft.). Now take that same plant, and put it into a 15 gallon container. You've effectively crammed a root structure that normally occupies 4.66 cubic feet of soil into 2 cubic feet of soil (~7.5 gallons=1 cubic foot).
Now, when considering root volume to soil volume, it's important to understand that in agricultural (in ground) settings, excess nutrients are carried out of that 6-8 inch zone in the soil strata by the process of leaching ("flushing" to the hydro guys). This doesn't happen with the commonly practiced "keep the soil moist" watering method utilized by most organic gardeners growing in living soil. There is very little to no drainage out of the bottom of the pot.
So what happens when there are excessive amounts of dissolved solids in the water used to irrigate your container plants? Over time, they begin to concentrate in the lower reaches of the pot, where the nutrient adsorbing roots are growing. Depending on how much of what is in the water, nutrient toxicity and/or unavailability (due to minerals precipitating out of solution) can occur. Trying to grow "large" plants in "small" containers with "long" veg' times only serves to compound these problems (again, root to soil volume).
IMO, this is why it's important for indoor gardeners growing in biologically active soils to know what's in their irrigation water. Especially those growing no-till or reusing their soil.
At a TDS reading of 25-30 ppm, you probably don't have much to worry about, if you can rely on the accuracy of your meter.
If you can find a municipal water report for your area, it may contain results for dissolved mineral content (Ca, Mg, etc...). Some do, some don't.
growerNshower
Well-Known Member
Thanks for the discussion waktoo, you are likewise a rarity on this platform!
I am growing in 200 gallon pots (48 inches wide, 24 inches deep) and I don't plant until June 1st-ish...not sure if they're becoming rootbound due to volume, but do I worry about the shape. I have been wondering for a while if I should be using wider and shallower pots, but with the 110+ temps on a SW slope, I worry about heat damage to roots...and I need a good mulch to help with this. I should probably put the pots level with the ground if anything to avoid overheating. Having said that, if solutes are concentrating in lower reaches of the pot, I guess my plants won't be affected with a 2 foot tall pot, since the nutrient roots only go down 6-8 inches?
As for watering, I just started using drip last year, and for some plants, I think I overdid the water some days, underdid it other days, so they pretty much experienced the worst of both worlds, lol.
My "calibration" was not really calibration in the sense that I adjust my instrument, but rather it lets me know what my reads are compared to a "standard," being a solution of known NaCl concentration. Since NaCl is soluble to 360 g/L, and my standard solution is 100-fold lower than that, I expect that >99.9% of the NaCl standard is in solution at 24 deg C when prepared/measured.
The water quality report from my irrigation source indicates the following:
TDS: 34 (mg/L)
Bicarbonate: 25 (mg/L)
Calcium: 4 (mg/L)
Mg: 1 (mg/L)
CaCO3: 10 (mg/L)
pH: 7.9 (I'm getting consistent reads of 7.0...hmm)
Na: 5.5 (mg/L)
Chlorine(Cl2): 0.5 (mg/L)
Chloride: 2 (mg/L)
Haloacetic Acids: 50-60 (ug/L)
Trihalomethanes: 50-70 (ug/L)
I heard from the local grow shop, dudes are adjusting their water to lower pH, so I guess that makes sense.
What do you think?
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All things considered, I'd say you're good man! Your ppm's are sooooooooo low. Wish I had your water...
As far as the pH goes, I would trust the water report over your meter. Given that you're gonna be watering a lot, I would adjust the water. Citric acid powder is great, cheap, a little goes a long way, and doesn't add any other "nutes" like many pH down solutions do (phosphoric acid for example).
growerNshower
Well-Known Member
Thanks for the consult brother. That makes a lot of sense. I happen to have some citric acid on hand actuallyAll things considered, I'd say you're good man! Your ppm's are sooooooooo low. Wish I had your water...
As far as the pH goes, I would trust the water report over your meter. Given that you're gonna be watering a lot, I would adjust the water. Citric acid powder is great, cheap, a little goes a long way, and doesn't add any other "nutes" like many pH down solutions do (phosphoric acid for example).
I would share my water if I could!Hey man. One more thing...
The pic's here indicate an issue with some immobile nutrient. From your soil report, it sure isn't calcium, but most certainly could be a lack of sulfur, micronutrient, or combination of micronutrients. While your soil does contain these elements, the high levels of soluble Ca, Mg, and K are probably having antagonistic affect on the adsorption of whatever it is you're missing. I really do wish I could diagnose your soil mix itself, but you're using materials and a recipe that I have zero experience with.
You may do well to anticipate this issue popping up again and be ready for it. Bio-Ag makes a great micronutrient concoction that can be applied as a foliar spray, which is how I would use it. It probably wouldn't be very effective added to the soil, given those high TDS levels. Foliar application puts it right where it's needed.
Knowing nutrient mobility is helpful in diagnosing plant nutrient deficiencies
Nutrients important for plant growth vary in their ability to move within the plant. Knowing how they move can be helpful when diagnosing deficiency problems.
growerNshower
Well-Known Member
Hey thanks for the heads up and cool nute chart.Hey man. One more thing...
The pic's here indicate an issue with some immobile nutrient. From your soil report, it sure isn't calcium, but most certainly could be a lack of sulfur, micronutrient, or combination of micronutrients. While your soil does contain these elements, the high levels of soluble Ca, Mg, and K are probably having antagonistic affect on the adsorption of whatever it is you're missing. I really do wish I could diagnose your soil mix itself, but you're using materials and a recipe that I have zero experience with.
You may do well to anticipate this issue popping up again and be ready for it. Bio-Ag makes a great micronutrient concoction that can be applied as a foliar spray, which is how I would use it. It probably wouldn't be very effective added to the soil, given those high TDS levels. Foliar application puts it right where it's needed.
Knowing nutrient mobility is helpful in diagnosing plant nutrient deficiencies
Nutrients important for plant growth vary in their ability to move within the plant. Knowing how they move can be helpful when diagnosing deficiency problems.www.canr.msu.edu
I'm still not sure what the issue was last year, but I did find some mold in several of the top colas, probably from the warm rains in late september...I'm wondering if the "nute def" was actually a mold issue. I also had what looked like bud end rot on one plant that didn't show the yellow leaf margins, perhaps due to calcium def, even though I didn't see classic leaf signs of a calcium def...perhaps the calcium def started in early-mid flower, so didn't show up on leaves? That particular plant had an open bottom pot and my native soil is very magnesium heavy serpentine...so a calcium def might make sense there, unrelated to the potting mix, and more related to high magnesium:calcium ratio in the native soil? Although I guess that conflicts with the shallow nute-root theory....not sure if this changes anything, but the pot was pretty small for the plant, about 75 gallons, and the plant yielded like 3-4 pounds.
Yeah, foliar is a great suggestion, I will keep an eye out and be waiting to apply. I'm thinking epsom salts and kelp and maybe some fulvic acid, should cover most of the micros and the sulfur. Were you thinking of the CytoPlus product from BioAG? That seems like a great foliar product.
How wide is a plant like that, compared to the pot? Didn't the roots grow out of the bottom? I have zero experience growing outdoors. I live in Colorado, in the mountains.
I'm unsure as to whether or not mold could have caused your "deficiency" issues. You are supposed to have higher levels of calcium available compared to magnesium, so the excess mag' could have affected proper calcium absorption. You're going to need to fix that imbalance over time.
Not the CytoPlus. TM-7.
growerNshower
Well-Known Member
Early still, but the girls seem to like the new soil amendments OK. I amended 1.5 months prior to transplant, just transplanted July 1st, 2 weeks ago, it's been 105+ degF last few days. I give a thorough watering every 1.5 days, but I have not been adjusting pH of the water...would like to, but not setup to do that right now. Old growth got a few necrotic spots, guessing the transplant stress/heat stress...but new growth coming in looking pretty good. Top 3-4 inches of soil gets very hot and dry, but stays moist and cool below that. I've been spraying down the girls every 3 days when sun goes down to remove potential pests/pathogens, and hopefully deliver some foliar trace minerals like calcium. Any thoughts?
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Mulch your pot(s). An inch or two of non-allelopathic (look it up) wood chips should suffice. This will greatly reduce evaporative loss and should help with soil temp's.
Also, with the steady high temp's you'll be experiencing, incorporating soluble potassium silicate into your foliar application regime will greatly reduce potential problems associated with heat stress. It also makes plants less susceptible to pathogenic and insect attack, and strengthens branches to support heavy flowers . While soluble potassium silicate is a synthetic product, it is approved by the NOP for use in organic food production (if the silica is sourced from sand).
I also ran across this the other day. Pretty interesting write up explaining what potassium silicate is and what it does for plants. If you didn't know already...
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growerNshower
Well-Known Member
Mulch: yeah, I've been pondering if I should mulch or not...I'm a bit worried about sources of pest contamination like mulch, but I know the girls could definitely use some shade on their soil.Mulch your pot(s). An inch or two of non-allelopathic (look it up) wood chips should suffice. This will greatly reduce evaporative loss and should help with soil temp's.
Also, with the steady high temp's you'll be experiencing, incorporating soluble potassium silicate into your foliar application regime will greatly reduce potential problems associated with heat stress. It also makes plants less susceptible to pathogenic and insect attack, and strengthens branches to support heavy flowers . While soluble potassium silicate is a synthetic product, it is approved by the NOP for use in organic food production (if the silica is sourced from sand).
I also ran across this the other day. Pretty interesting write up explaining what potassium silicate is and what it does for plants. If you didn't know already...
Silicon: I used silicon dioxide as amendment to the soil. Do you think it will add anything to foliar with Potassium Silicate? I was thinking of doing a foliar with GH ArmorSi (Pot Silicate) and Floralicious Plus (aminos, kelp, vitamins). Also, do you rinse some time after your foliar applications?...like maybe apply in eve, rinse in morning...or apply first light and rinse after they dry?
WHAT did you put in your soil?
I’ve personally only used pot’ sil’ as a foliar. If you did want go that route, apply it separately from the FP. Don’t mix them together. You could alternate between applications. I never “rinse” after any foliar application. Never even heard of that before. Always do foliar applications after the sun goes down. And don’t over apply foliars...
dbz
Well-Known Member
Virginia Tech Soil Testing Lab
MustangStudFarm
Well-Known Member
I'll pop in with my 2 cents. EM1 or LABS is great for this. It also helps with WPM and other fungi.