Hydro workshop: Nutrients and supplements

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NPK and micronutrients

The three main nutrients every plant needs are NPK:

  • Nitrogen (N): promotes vigorous, lush green growth
  • Phosphorus (P): healthy roots, also key for metabolism and transition into fruiting phase
  • Potassium (K): good water management, robustness against temperature, drought, disease, insects

All necessary, but ideal strengths vary by plants and by phase of growth. Other micronutrients are also needed in trace amounts, but any purchased nutrient solution system will include them.

Nutrient formulas: Grow and Bloom

We often model a plant’s basic needs as fitting one of two patterns, ‘grow’ or ‘bloom’. A ‘grow’ formula has relatively high NK and lower P, stimulating overall growth to build up the plant without triggering flowering or fruit/seed production. A ‘bloom’ formula has lower N and higher PK to encourage and support sustained flowering and fruiting. Ex. A grow formula might have N-P-K = 7-4-10, and bloom might have 4-8-7.

  • Plants less than two weeks old: just water or very weak Grow solution.  Some supplements are helpful but in general you want to take it easy and not overwhelm baby plants.
  • Herbs and leafy greens: slightly weak Grow solution.
  • Tomatoes, peppers, and other fruiting plants: full strength Grow solution until they reach full size and make first flowers, then switch to Bloom.



Certain plants have other specific needs. For example, nutrient solutions have calcium and magnesium as a trace mineral but tomato and pepper plants often need more than it provides. CalMag products are the most commonly needed supplements. If no access to a CalMag supplement, you can try supplementing with a foliar spray of 1 tsp. plain epsom salts (Magnesium Sulfate) to 1L water.

Personally, in addition to Optimum Hydroponix Grow A/B and their CalMag product OptiCal-Mg, I use their Supermax B1, which is a seaweed-based organic supplement that provides some special micronutrients as well as microbial action.  In my experience, it’s a great tonic for relieving plant stress and helping roots make a comeback after they’ve gone through something.  I also use their Sonic Bloom product which is a very potent PK fertilizer for flowering and fruiting.

Actually I don’t buy the Optimum Hydroponix Bloom formula because I find that the grow and bloom formulas are very close together for this brand.  I approximate a bloom formula by using less grow than usual and supplementing with Sonic Bloom, counting on the Optical and the Supermax B1 to pick up any slack in micronutrients.

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