Hydro and soilless grows are a different beast when it comes to pH. If you grow soilless, say in coco, the optimal pH level at the root zone should be somewhat lower than in soil, between 5.5–6.5. The same goes for all methods of hydro.
Measure the pH after you add any nutrients or amendments as they will change the pH value of your water. After you mix the solution, use the pH meter or drops to test the pH level. If you are growing hydroponically, test a sample from your water reservoir a few minutes after you add your nutrients.
Managing pH level means testing the water or nutrient solution and adjusting it accordingly. This may sound complicated, but it really isn’t.
If you grow purely organically—where you do not administer liquid nutrients—pH is less of an issue. If you’re using amended and composted soil with organic matter, the microorganisms within will make the nutrients more available to the roots. However, most growers using standard potting mixes and liquid nutrients will indeed have to reckon with pH.
When growing in coco, perlite, or hydroponically, you are in charge of administering nutrients directly to the root zone via the water, which means that huge pH fluctuations are more of a risk than in soil. The inert media used in hydro and soilless grows merely retains water and provides support for the roots of your plants. So when administering nutrients, be careful that you don’t overload your plants.
With these methods, it is just as important that you allow the pH level to fluctuate across the acceptable range to support nutrient uptake. For example, in hydro, calcium and magnesium are mostly absorbed at pH levels above 6, while other nutrients like manganese prefer a slightly lower pH.
Given the alkalinity of most tap water, most of the time you will probably need to lower your pH as opposed to raising it. This means you could potentially get by with just a bottle of pH down. Note that you will normally need very small amounts of these pH-adjusting products to see results. Add the required amount and then test your water with the meter or drops. When everything is in the clear, you can feed your plants.
If you grow in soil, the optimal pH level for the root zone is between 6.0 and 7.0. However, there is no set number within this range that is “best”. Instead, it can be good to allow for some natural fluctuation within this window to support optimal nutrient uptake. So as you adjust, try a slightly different reading each time. You can, for example, adjust your pH to 6.2 for one watering, then 6.6 the next. As long as it stays within 6.0–7.0, you should be fine. Soil is also more forgiving when it comes to pH imbalances, but it can only give so much.
pH is a measure of how acidic or alkaline something is. The pH scale ranges from 1–14, with a pH of 7 being neutral (the pH of pure water). If pH is lower than 7, a substance is considered acidic (think vinegar or lemon juice). If the pH is higher than 7, the substance is alkaline, as is the case with soaps, bleach, and ammonia.
In the world of gardening, pH both affects and is affected by everything. Indeed, the entire process of growing plants is a study in the physical dance of pH balance.