Soil and Compost forum: PH problems in my potting mix.

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Gimlett
Nov 2, 2017 8:46 AM CST
I live in the state of Massachusetts where it is legal for me to grow Cannabis, which I am growing in containers using Fox Farms Ocean Forest potting mix. I water with rain water only. The rain water PH ranges from 6.8 - 7.1.

My plants keep getting sick because the PH goes really low - around 5.5 - 5.8. Most plants love this stuff, but I guess cannabis is more picky about PH issues. I also have PromixBX which has the same problem. Both of these products are prescribed by cannabis growers specifically. I am starting to realize just how much cannabis growers know... They tell me to just add lime. I did that. How much is too much? Nobody can say!

Can anyone help me either (preferably) figure out how to stabilize the PH of my current grow media or point me to a decent mix or recipe for a home made mix that will not have PH problems? I would like to get away from peat based products, but that is hard to find. What else is there?

Any advice would be greatly appreciated.
Name: Joseph
Delaware USA (Zone 7a)
Morning Glories Adeniums Region: Delaware Salvias Composter Container Gardener
Garden Photography Plant and/or Seed Trader Region: United States of America
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Gerris2
Jan 9, 2018 8:53 AM CST
Maybe a little garden lime would raise the pH level in your potting mix. Experiment a little.

That's cool you can legally grow Cannabis sativa. I always thought it was a pretty plant.
Name: Will Creed
NYC
Professional indoor plant consultan
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WillC
Jan 25, 2018 4:13 PM CST
I don't know from direct experience, but online sources consistently recommend pH ranges of 5.5 to 6.0 when grown hydroponically and 6.0 to 6.5 when grown in potting mixes.

Are you also checking the pH of the soil? Over time, water will change the soil pH but it is the soil PH that matters most.

Horticultural lime will increase the pH. How much you use will depend on how much the pH needs to be raised and the volume of the soil.
Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
I now have a book available on indoor plant care
Name: Jason
Oregon (Zone 8b)
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TomatoTango
Jan 31, 2018 10:32 AM CST
Are you sure it's sick and not a nutritional deficiency? That potting mix may not have sufficient nutrition for the plant, especially if you put it outside. Are you feeding the plants anything?
Name: Will Creed
NYC
Professional indoor plant consultan
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WillC
Feb 6, 2018 1:57 PM CST
Jason - Improper pH is what leads to nutritional deficiency. Certain nutrients are insoluble and unavailable to plants if the soil pH is outside the proper range. It's not that more nutrients need to be added; it is that the pH needs to be corrected so the nutrients that are already there can be absorbed and used by the plant. Whenever a nutrient deficiency is suspected, always start by checking the soil and water pH first.
Will Creed
Horticultural Help, NYC
www.HorticulturalHelp.com
I now have a book available on indoor plant care
Name: Jason
Oregon (Zone 8b)
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TomatoTango
Feb 12, 2018 9:42 AM CST
WillC said:Jason - Improper pH is what leads to nutritional deficiency. Certain nutrients are insoluble and unavailable to plants if the soil pH is outside the proper range. It's not that more nutrients need to be added; it is that the pH needs to be corrected so the nutrients that are already there can be absorbed and used by the plant. Whenever a nutrient deficiency is suspected, always start by checking the soil and water pH first.


I've grown several marijauana plants. I got a picture of an Afghan that's 12' high from last year. They absolutely can and will eat all of the nutrients out of the soil. Especially a potting mix. And that pH isn't wildly off for cannabis unless you're giving it cal/mag, then it's 6.5. I believe testing soil pH to be an utter waste of time. Just give the plant the right pH when you water or feed.
Name: Joseph
Delaware USA (Zone 7a)
Morning Glories Adeniums Region: Delaware Salvias Composter Container Gardener
Garden Photography Plant and/or Seed Trader Region: United States of America
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Gerris2
Feb 12, 2018 11:11 AM CST
Holy moly, twelve feet tall?! That must be some awesome kickapoo joy juice you're feeding it. Would you share your method, please? I don't grow Cannabis but grow many annual and perennial plants in pots so am always happy to learn new things in growing them.
Name: Jason
Oregon (Zone 8b)
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TomatoTango
Feb 12, 2018 11:27 AM CST
Raised beds with good fertilizers like rock powders, a few liquid feedings, I pH adjust feedings and water, and make sure beds are amended with manure/compost.

Thumb of 2018-02-12/TomatoTango/2fd3fe

Name: Joseph
Delaware USA (Zone 7a)
Morning Glories Adeniums Region: Delaware Salvias Composter Container Gardener
Garden Photography Plant and/or Seed Trader Region: United States of America
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Gerris2
Feb 12, 2018 3:39 PM CST
Great information, thanks, Jason! What brand liquid fertilizer?
Name: Jason
Oregon (Zone 8b)
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TomatoTango
Feb 12, 2018 6:35 PM CST
Gerris2 said:Great information, thanks, Jason! What brand liquid fertilizer?


For liquid feedings I would recommend Dr. Earth or Neptune's Harvest for cheap end and FoxFarm for higher end. I wouldn't pay more $$ than that, and I'm sure there are dozens of other products that are very good. Make sure to pH adjust it.

Horse or cow manure are like $10 for a truckbed off craigslist and make sure your bed has a good foundation like peatmoss, compost, perlite or vermiculite, and brown matter like leaves. It should have earthworms in it and look alive.
Name: Joseph
Delaware USA (Zone 7a)
Morning Glories Adeniums Region: Delaware Salvias Composter Container Gardener
Garden Photography Plant and/or Seed Trader Region: United States of America
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Gerris2
Feb 12, 2018 7:20 PM CST
What is a desirable pH for annuals, in general? Near neutral 7.0? How does one go about testing, pH strips? If it is too acid or basic, how do you adjust it?

I appreciate the advice and you sharing your experience, very much so.
Name: Jason
Oregon (Zone 8b)
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TomatoTango
Feb 12, 2018 7:40 PM CST
Gerris2 said:What is a desirable pH for annuals, in general? Near neutral 7.0? How does one go about testing, pH strips? If it is too acid or basic, how do you adjust it?

I appreciate the advice and you sharing your experience, very much so.


Every plant is different and has very specific ranges they like. I don't adjust soil pH. I don't care what it is. I bring in 5 ingredients and mix them in a raised bed 12" over clay. It works great.

When I water or liquid feed I adjust it with a digital pen that reads pH. I mix it in 5 gallon buckets and deep water or dispense in cups to smaller plants. Almost all plants like an acidic base, including vegetables. When the plants eat they will find the exact pH at the root base after you've been watering that spot for awhile.

Vinegar is cheap and will lower the pH to whatever you need. If you're feeding a specific nutrient or believe your plant is deficient, lower the pH of the water accordingly. All of these numbers can be found online easily. And follow the instructions on the bottle when feeding, or halve it. I primarily grow tomatoes with these methods.

Name: Joseph
Delaware USA (Zone 7a)
Morning Glories Adeniums Region: Delaware Salvias Composter Container Gardener
Garden Photography Plant and/or Seed Trader Region: United States of America
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Gerris2
Feb 12, 2018 7:52 PM CST
Thanks again, much appreciated!
Name: Baja
Baja California (Zone 11b)
Cactus and Succulents Seed Starter Foliage Fan Xeriscape Container Gardener Hummingbirder
Native Plants and Wildflowers Garden Photography Region: Mexico Plant Identifier Forum moderator Plant Database Moderator
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Baja_Costero
Feb 12, 2018 8:28 PM CST
I'm with Jason. Soil pH is not something I measure or care about in pots. There are two products made by Seachem for adjusting and buffering pH in planted aquaria. You will find them (and various pH test kits) in your local pet/aquarium store. I use their Acid Buffer to adjust our very alkaline well water to pH 6 for all my potted plants (mostly succulents). The buffer in the water resists changes once it has been adjusted. You can use cane vinegar if you like. Various acids work for this purpose. The corresponding Alkaline Buffer is bicarbonate-based.

To measure the pH I use indicator drops by API which work in the range of 6-7.6 (perfect for my needs). You put three drops in a tube of water and the color goes from blue to green to yellow as the pH drops to 6.
[Last edited by Baja_Costero - Feb 12, 2018 8:29 PM (+)]
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