Lowering soil pH for seedlings

OldManRiver · Apr 28, 2020

I have some seedlings that have been struggling. The soil, Happy Frog, has a pH of about seven, as measured by a HomeDepot gauge. Before you diss that, I have used these for some years for soil, and they are close enough for government work; the soil pH is higher than optimum. I watered in aluminum sulphate twice, but the pH is being very resistant. In trying to lower the pH, I have overwatered the plants, and they are hurting. I think they will come back, but I'm looking for advice on how best to nurse them. They are 6 inches tall, on their four or fifth set of leaves, bottom two sets are toast. They are in 16 ounce solo cups, several drainage holes each. At this point, I'm watering them a measured 1/4 cup every three days, when soil is dry three inches down. The last watering, I gave a teaspoon of Alaska fish ferts in a gallon mix. They got 1/4 cup of that mix. The overwatering was almost three weeks ago now, and now they are just stalled. They have looked like that for over a week, except that the lower leaves originally weren't dead. LOL. They are NOT clawed down; the remaining leaves are flat or praying up like the should be, and color is OK. Not great, but OK. Lights are HLG 240W quantum boards, 26 inches up. One is a 3000K, the other a 4000k. Both are at or near full output. I have tomatoes, basil and peppers in the same soil, under the same lights, and they are mostly doing just fine. All plants have had the same water regimine, some of the tomatoes had some overwatering damage, too, but they are all recovering. Room temp is 65 at night, up to 72-3 in the day. They are on a seedling mat that is set to 77*. RH is about 50-60 percent, depending on the day.

I really want to get the pH down 1/2 point, but I can't do that without watering heavily, and you can see what that did.

Thoughts?

growsince79 · Apr 28, 2020

Every soil on earth has a ph of about 7 as measured by homedepot gauge. IMO they are worthless. The $4 ph tape or drops works better.

mancorn · Apr 28, 2020

1 teaspoon of Alaska fish ferts in a gallon mix will take the pH of that gallon down to about 4. (I use it just to lower my pH and I can get 2 gallons to drop a full point with just 1/8 tbs.) The Fox Farm soil has added oyster shell to buffer the pH, so you're not going to be able to significantly chance the soil pH. I'll bet that the pH of the soil is actually closer to 6.5, and you're fine.

I know you don't want me dissing on your meter, but it's simply not that accurate, so don't try dropping your pH relying on your meter. Soil will natural buffer your water pH, and you'll end up with more problems then you'l be solving. You can buy a cheap meter for less then $20, which will be be fairly accurate (if you keep it calibrated). You'll defineatly want to be checking your fish fert water and combining it with something like kelp to balance out it's super low pH (or use a pH up).

OldManRiver · Apr 28, 2020

mancorn said:
1 teaspoon of Alaska fish ferts in a gallon mix will take the pH of that gallon down to about 4. (I use it just to lower my pH and I can get 2 gallons to drop a full point with just 1/8 tbs.) The Fox Farm soil has added oyster shell to buffer the pH, so you're not going to be able to significantly chance the soil pH. I'll bet that the pH of the soil is actually closer to 6.5, and you're fine.

I know you don't want me dissing on your meter, but it's simply not that accurate, so don't try dropping your pH relying on your meter. Soil will natural buffer your water pH, and you'll end up with more problems then you'l be solving. You can buy a cheap meter for less then $20, which will be be fairly accurate (if you keep it calibrated). You'll defineatly want to be checking your fish fert water and combining it with something like kelp to balance out it's super low pH (or use a pH up).

I appreciate your input. I have checked the meter against the chemical soil test kits, and it's indications are accurate enough for garden use. It's not a digital readout, but it's indicating over 7. I've used these for several years. I've had plants suffering from both soil that was too acid (Kellogs organic from Home depot)it indicated that, I added sweetener, and the plants perked rightup. I've had soil that was alkaline (Happy Frog), it indicated that, I added sulphate, and they perked up. I've seen this problem with Happy Frog for a couple years now, and I won't be buying it again.

Simply lowering the pH of the water has never made much difference for me. As you note, the soil seems to buffer it.

That's good info about the oyster shell buffering the pH. That's probably the issue. I need to get them outside in the garden, where the soil is better, but its still a bit cold.

OldManRiver · Apr 28, 2020

growsince79 said:
Every soil on earth has a ph of about 7 as measured by homedepot gauge. IMO they are worthless. The $4 ph tape or drops works better.

That is simply untrue. I've compared the meter against the chemical test kits, and they confirmed the results. As I note in the previous post, in just the last year, the meter has advised me to sweeten some soil and acidify some other soil. In both cases, when I did that, I achieved the desired improvements in health. If you check the pics in my sig, I'm not a rookie here.

Certainly other test methods are perhaps more precise. The meters are much quicker to use. For the record, they work best in moderately moist soil, and they need a couple minutes to come to the final reading.

For the record, I have decided that Happy Frog is dog shit, and will not be ordering agin.

MIMedGrower · Apr 28, 2020

Both my cheap probe moisture/ph meters always read 7 ph. They are both wrong. Every bag of ocean forest and happy frog i have used came out at 6.5 runoff with gh ph drops.

Something else was likely wrong with the grow and then you raised the ph with chemicals and the problems are now stacking in my opinion.

OldManRiver · Apr 28, 2020

MIMedGrower said:
Both my cheap probe moisture/ph meters always read 7 ph. They are both wrong. Every bag of ocean forest and happy frog i have used came out at 6.5 runoff with gh ph drops.

Something else was likely wrong with the grow and then you raised the ph with chemicals and the problems are now stacking in my opinion.

Well, I have only applied Aluminum sulphate, which normally lowers pH. I gave them one feeding of Alaska fish ferts, 1 tsp to a gallon. I checked the Happy Frog sometime back with the chem test, it was over 7. I'll get another kit, see what it says.

MIMedGrower · Apr 28, 2020

OldManRiver said:
Well, I have only applied Aluminum sulphate, which normally lowers pH. I gave them one feeding of Alaska fish ferts, 1 tsp to a gallon. I checked the Happy Frog sometime back with the chem test, it was over 7. I'll get another kit, see what it says.

Really no need to micro manage ph in buffered potting soil. If the ph os rising it could mean they are hungry and could use a bit more feed. Looking back at your pics the tops look good but the low first leaves are deficient. Might just need to transplant up to fresh soil or another light feed.

I never heard of using aluminum sulphate before. Mag sulfate is usually used. Epsom salts.

OldManRiver · Apr 28, 2020

MIMedGrower said:
Really no need to micro manage ph in buffered potting soil. If the ph os rising it could mean they are hungry and could use a bit more feed. Looking back at your pics the tops look good but the low first leaves are deficient. Might just need to transplant up to fresh soil or another light feed.

I never heard of using aluminum sulphate before. Mag sulfate is usually used. Epsom salts.

Aluminum sulphate is pretty common. It's sold to turn hydrangeas blue by making the soil acidic. Iron sulphate, mag sulphate are alternatives.

I found some Ocean Forest at the hardware store. I repotted to that. I'm done screwing around with Happy Frog. I've used it for several years, and the last two seasons it is disappointing me. It addition to the pH, it doesn't wet down very well. It used to be fine, maybe they changed the mix.

Madbud · Apr 29, 2020

Move your light higher or turn it down, canoeing leaves and light burn everywhere.

OldManRiver · Apr 29, 2020

So, following up on the accuracy of the meter, I got a soil test kit, and it confirms the pH readings of the meter. The first pic is of Fox Farms Ocean Forest, the second is the Happy Frog, the last is the kit. You can see that the Happy Frog, in particular, is pretty alkaline, as the meter indicated. Last year, I had to does this pretty heavily with sulphate before the plants in it started thriving. I remain convinced that the meter is at least usefully accurate, and that the Happy Frog we're getting on the west coast is shit for growing weed. There could easily be regional differences; it wouldn't surprise me if this is built and distributed regionally.

I have test strips on order, won't be here for a week, and I'll get a third data point then.

@MIMedGrower

OldManRiver · Apr 29, 2020

Madbud said:
Move your light higher or turn it down, canoeing leaves and light burn everywhere.

The lights are 26" above the plants, and this looks nothing like light burn to me. These are quantum board lights, not HID. The affected leaves are on the bottom, and the primary issue is overwatering damage. There are six species of plants under the lights, the others are fine. Light burn would be frying the tomatoes, peppers and basil as well, if that were the issue, is my belief. I've been wrong before, open to input.

growsince79 · Apr 29, 2020

OldManRiver said:
The lights are 26" above the plants, and this looks nothing like light burn to me. These are quantum board lights, not HID. The affected leaves are on the bottom, and the primary issue is overwatering damage. There are six species of plants under the lights, the others are fine. Light burn would be frying the tomatoes, peppers and basil as well, if that were the issue, is my belief. I've been wrong before, open to input.

I think you nailed it about the over watering. I've noticed my plants can't absorb N and cal when it's too wet. I'm using cocoloco/perlite now without any problems.

OldManRiver · Apr 29, 2020

growsince79 said:
I think you nailed it about the over watering. I've noticed my plants can't absorb N and cal when it's too wet. I'm using cocoloco/perlite now without any problems.

Oh, they are definitely overwatered. That was the original question, how to nurse them best, which no-one has responded to meaningfully. I changed out the soil, and will just be careful after that. The discussion tracked sideways as to whether the original problem, soil pH, which caused the overwatering as I tried to address it, was accurately measured by the Home depot meter, which the above pics show was correct.

Madbud · Apr 29, 2020

Using this water?

Homesteader · Apr 29, 2020

Without looking too much into your grow or the plant health, if you are looking to drop the pH to a measurable level without throwing the nutrients out of whack, your best bet would be to use a few handful of straight 100% peat. It generally is about a 5 or 5.5 so a few handfuls will drop your mix by a few fractions depending on the size of the pots

OldManRiver · Apr 29, 2020

Madbud said:
Using this water?View attachment 967599

no, i'm in the seattle area now. City water is rainwater, neutral pH, TDS around 140. Incredible water for making beer, incidently.

OldManRiver · Apr 29, 2020

@MIMedGrower @growsince79 My test strips came in from Amazon, they confirm that the Happy Frog is about 7.5 and the Ocean Forest is about 7.0. Which is more or less what the meter said. YMMV.

MIMedGrower · Apr 29, 2020

OldManRiver said:
@MIMedGrower @growsince79 My test strips came in from Amazon, they confirm that the Happy Frog is about 7.5 and the Ocean Forest is about 7.0. Which is more or less what the meter said. YMMV.

Thats weird. Even the last bags of OF i bought a few months ago were both 6.5 out of the bag and after 10 weeks flowering.

OldManRiver · Apr 29, 2020

MIMedGrower said:
Thats weird. Even the last bags of OF i bought a few months ago were both 6.5 out of the bag and after 10 weeks flowering.

Yeah, I'm pretty stunned. Again, I wonder if they are made regionally or something. With both Happy Frog and OF being marketed heavily to the weed community, I am very surprised. In contrast, the bags of Kellog Organic I got from Home Depot last year was under 6.

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