Jack Harer
Well-Known Member
PH in soil seems to be a very misunderstood subject here, and I hope I can help more to understand the actual mechanics of it. Hopefully, this won't ruffle too many feathers and will help the soil growers understand the true nature of how pH works in soil, and avoid costly mistakes or mortality.
First you'll need a GOOD pH meter/pen. This is a one time cost, and is an investment that will pay dividends in the long run. If you are going to be a grower you can't afford NOT to have one. Do not worry about getting a meter for PPMs, as PPMs really do not translate into soil well.
You need to be concerned with the pH of the ACTUAL MEDIA, not the water going in or coming out. The soil will buffer the pH of whatever goes in, to that of the soil. This is not an instant change, the change takes a few minutes to occur, so the run off will not be an indicator, as it has not sat in contact with the soil long enough to be affected. What is a buffer? A buffer is something that resists change to pH, and will bring the pH of the surroundings to it's pH value. A buffer is extremely stable. A good example of a buffer is lime. Lime is very alkaline, and will change the pH of an acid. Since almost all soil-less mixes are peat based, they are acidic from the start. To counteract this acidity and bring the pH value up to that which plants need, most manufacturers will add lime. Lime comes in several forms, usually either dolomite lime or garden lime. They are both forms of Calcium Carbonate, the dolomite having a higher level of magnesium. Garden lime is usually a very fine powder where dolomite is usually an aggregate or larger gravel like pieces. Oyster shell is another good source, as are egg shells, but both of these are very slow acting.
Never trust the manufacturer of your soil (unless you made your own) to have added enough lime!!! Always check it yourself at the start of every grow to verify it. The best time to check the pH of your soil is when you make your mix at the beginning of the grow. If you are using organic fertilizers that need to be mixed into the soil, add them all, then check the pH. If you are going to use a chemical salt based nutrient, you can skip this step. After you have prepared your soil, and are ready to plant, take about 3 or 4 tablespoons of your soil and put that into a small container just large enough for the pH meter to fit into. Add enough distilled water to that so that the soil is covered by 1/2” of water. Shake it thoroughly and let it set for about half an hour. Then check the pH of that. This is the pH of your soil. You want this to be 6.8 ideally. If it's low, add lime to the entire batch of soil, and re-check the pH. Do this in BABY STEPS until the desired pH value is set, Once the pH of soil is set, it is extremely stable, and under normal conditions, will not change during the duration of a grow. This is going to be the buffer that will adjust the pH of your watering/nutrient solution. You can now plant the girls.
To avoid shocking the roots, if your tap water has a high pH (over 7.5) you'll want to adjust it closer to 6.8, but even if you don't, the soil will do it in a few minutes. As the water you put in sits in contact with the soil, the pH of that water will be brought to that of the soil, not the other way around. So obviously run-off water will not be an accurate indicator, as it just passed through the soil, and was not in contact with it long enough to matter. You want to check the pH of your water AFTER you have added your nutes. Adjust it with any pH down available at any aquarium shop or nursery. If it's safe for fish, you can use it on your plants. You will want to be using tap water whenever possible to take advantage of the trace elements and dissolved mineral content. RO or distilled water will only cause more mineral deficiencies than anything.
If you follow these procedures, and don't go adding all sorts of shit to “help the plants”, pH will be a non-issue for the whole grow. If you do see what you perceive as a problem, always check the pH of that pot just to eliminate that as a cause, but nutrient lock out in properly mixed soil due to pH is really quite rare. Nutrients are so interdependent, an over abundance of one can lock out another, or a deficiency of one can do the same. Nutrition is a delicate balance.
First you'll need a GOOD pH meter/pen. This is a one time cost, and is an investment that will pay dividends in the long run. If you are going to be a grower you can't afford NOT to have one. Do not worry about getting a meter for PPMs, as PPMs really do not translate into soil well.
You need to be concerned with the pH of the ACTUAL MEDIA, not the water going in or coming out. The soil will buffer the pH of whatever goes in, to that of the soil. This is not an instant change, the change takes a few minutes to occur, so the run off will not be an indicator, as it has not sat in contact with the soil long enough to be affected. What is a buffer? A buffer is something that resists change to pH, and will bring the pH of the surroundings to it's pH value. A buffer is extremely stable. A good example of a buffer is lime. Lime is very alkaline, and will change the pH of an acid. Since almost all soil-less mixes are peat based, they are acidic from the start. To counteract this acidity and bring the pH value up to that which plants need, most manufacturers will add lime. Lime comes in several forms, usually either dolomite lime or garden lime. They are both forms of Calcium Carbonate, the dolomite having a higher level of magnesium. Garden lime is usually a very fine powder where dolomite is usually an aggregate or larger gravel like pieces. Oyster shell is another good source, as are egg shells, but both of these are very slow acting.
Never trust the manufacturer of your soil (unless you made your own) to have added enough lime!!! Always check it yourself at the start of every grow to verify it. The best time to check the pH of your soil is when you make your mix at the beginning of the grow. If you are using organic fertilizers that need to be mixed into the soil, add them all, then check the pH. If you are going to use a chemical salt based nutrient, you can skip this step. After you have prepared your soil, and are ready to plant, take about 3 or 4 tablespoons of your soil and put that into a small container just large enough for the pH meter to fit into. Add enough distilled water to that so that the soil is covered by 1/2” of water. Shake it thoroughly and let it set for about half an hour. Then check the pH of that. This is the pH of your soil. You want this to be 6.8 ideally. If it's low, add lime to the entire batch of soil, and re-check the pH. Do this in BABY STEPS until the desired pH value is set, Once the pH of soil is set, it is extremely stable, and under normal conditions, will not change during the duration of a grow. This is going to be the buffer that will adjust the pH of your watering/nutrient solution. You can now plant the girls.
To avoid shocking the roots, if your tap water has a high pH (over 7.5) you'll want to adjust it closer to 6.8, but even if you don't, the soil will do it in a few minutes. As the water you put in sits in contact with the soil, the pH of that water will be brought to that of the soil, not the other way around. So obviously run-off water will not be an accurate indicator, as it just passed through the soil, and was not in contact with it long enough to matter. You want to check the pH of your water AFTER you have added your nutes. Adjust it with any pH down available at any aquarium shop or nursery. If it's safe for fish, you can use it on your plants. You will want to be using tap water whenever possible to take advantage of the trace elements and dissolved mineral content. RO or distilled water will only cause more mineral deficiencies than anything.
If you follow these procedures, and don't go adding all sorts of shit to “help the plants”, pH will be a non-issue for the whole grow. If you do see what you perceive as a problem, always check the pH of that pot just to eliminate that as a cause, but nutrient lock out in properly mixed soil due to pH is really quite rare. Nutrients are so interdependent, an over abundance of one can lock out another, or a deficiency of one can do the same. Nutrition is a delicate balance.
