Correct pH for Hydroponics

Author: Scott  

Hello I was wondering what the correct pH would be for Vegetative and Flowering Tomatoes.


Hi there

Good Question.

In soil, the minerals are less available, and depending on soil types and the type of fertiliser, all plants can have a variety of pH’s that plants will do well, or do very badly, at.

However in Hydroponics, only the most soluble form of a nutrient component is used. E.g. Phosphoric Acid for Phosphorus is only Phosphorus, and is very available and very soluble being a true liquid. As all the elements are at their best, we can then look at the availability at the ideal.

In Hydroponics, nutrients are very available in the range of 6.0 to 7.0 pH, and the best is 6..3pH


ph of between 6 and 7 is safe – 6.3 is ideal

When mixing a pre-made formula with town water (usually in the range of 7.2-8.0) the agronomist/chemist will design the nutrient to fall within the 6-7pH range. From there it is likely to rise in almost every situation, except in the case of very low light, such as shade or long periods of cloud, and also in some varieties with a heavy demand for potassium during flowering. Generally, people use pH up when they have used too much pH down, and I always question anyone buying pH up to see if they really need it, or need to increase their lighting.

In some cases a pH of 5.5-6.0 is recommended for people using an alkaline media such as Rockwool. Be aware of any information relating to pH may be written by those who use Rockwool and translate it to other medias. My preference with Rockwool is to pre-soak slabs in pH below 5.0 and then rinse. I then use a large syringe to suck out moisture from the slab, to test the difference between my pH mixed up, and the pH in the slab itself. This can be applied to a lot of medias, but don’t damage the structure or the roots by doing it everyday. Common sense always applies.

Hope that helps.


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