Hi Guys,
I started to listen to your podcast a couple months ago and I really dig it. I have a problem I’m hoping you can help with. I can’t get my pH runoff to go down. This is only my second grow. Clones in organic soil in a 2×4 tent. Using Coast Of Maine Platinum grower’s mix with a Hanna checker plus pH pen. I was pH Downing my water to between 5.8-6.2. I thought I was having nutrient deficiency but the owner of the local hydro supply store said it could just be the wrong pH and to check the runoff. I checked the runoff and it was over a point higher than the input water. So next time I added more pH Down and still too high. My runoff is between 6.8-7.1 with my input being 5 or 4 or even 3! Why will it not change? One of my plants has a Boron deficiency and I think if my pH goes down then it should go away. Thanks for any help you can give. Peace and Health.
Stoner Si
pH in soil and enriched mixes works differently than pH in inert media like coco or rockwool.
An enriched soil mix like you are using usually has a lot of buffers, microbes and other stuff in there that will stabilize and manage the soil pH all on its own.
The minerals and cation exchange capacity of your soil will act as a buffer to hold pH in a set range. The microbes in the mix are also working to control the pH of their environment and keep it where they are happiest.
In other words, you can’t manipulate soil pH like you can in coco or hydro becase the microbes and chemistry in the soil are working to maintain pH balance all on their own. When you try to lower your ph, these forces are working against you.
The good news is… if you’ve got decent quality soil and a healthy microbe population, you don’t need to manipulate your soil pH. In fact you are probably better off NOT trying to manipulate soil pH. You’ll have a much easier time if you just keep your microbes happy and try to keep the pH of your input water in a reasonable range.
Long story short… don’t try to chase pH when you are in a buffered soil or enriched mix. Instead, deploy lots of soil microbes and let them manage your soil pH for you. Just try to keep your nutrient inputs balanced and water them in at a reasonable pH so they are plant available.
Most peat based mixes are amended with lime or oyster shell flour which are carbonate sources which hold the ph right about 7 or a little under. This is the ph buffer, it won’t allow ph to become overly acidic. Your mix has a dolomite lime so that’s why she won’t budge. Microbial communities around the roots are able to change the ph at the root level to allow for different nutrients to be uptaken by the plant. Is this a water only soil or are you suppose to top dress every now and again, bigger pot might help as well(more soil). A compost tea or a product like recharge might do the trick. Some folks have luck just watering in some molasses to kick start the microbe colony. If you continue to run this grow style you might want to look into a product like bioags tm7 or buildasoil big 6 which contains the micronutrients chelated in humic and fulvic acids. Or look for other amendments high in boron to top dress in. Just know topdressing takes time for the microbes to make the nutrients available as opposed to chelated nutrients.