Hoagland solution is a complete nutrient solution described by Dennis Hoagland and Daniel Arnon in their 1950 University of California circular, "The water-culture method for growing plants without soil". It is one of the most cited recipes in plant science and is often used at half strength as a research control.
In practice
Solution 1 uses calcium nitrate, potassium nitrate, monopotassium phosphate and magnesium sulfate, plus iron and a micronutrient mix. It works out to roughly 210 mg/L (ppm) N, 31 P, 235 K, 200 Ca, 48 Mg and 64 S. Solution 2 replaces part of the nitrate with ammonium phosphate. For cannabis, it is a sound educational starting point. Most modern cannabis recipes run more phosphorus and magnesium, and replace the original iron source with a modern chelate.
Solution 1 macros in mmol/L: 15 N, 1 P, 6 K, 5 Ca, 2 Mg, 2 S.
Don't confuse with
- Commercial "Hoagland" powders: may differ from the original in micronutrients or iron form.
- Feed chart: a product schedule, not a defined recipe.
Calcium nitrate is the standard hydroponic calcium source, supplying about 19% calcium and 15.5% nitrogen, mostly as nitrate.Potassium nitrate (KNO3) is a soluble fertiliser salt supplying about 13% nitrogen as nitrate and 38% potassium, used in both veg and flower feeds.Monopotassium phosphate (MKP, KH2PO4) supplies about 22.7% phosphorus and 28.7% potassium with no nitrogen, and is the base of most PK boosters.Magnesium sulfate heptahydrate, sold as Epsom salt, is the common hydro magnesium source, supplying about 9.9% magnesium and 13% sulfur.A micronutrient is an essential element plants need only in trace amounts, below a few mg/L: iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel.Nitrate (NO3-) is the main form of nitrogen in hydroponic and soilless feeds; its uptake tends to push root-zone pH upward.Phosphate is the ionic form in which plants absorb phosphorus, mainly H2PO4- at the normal root-zone pH of 5.5-6.5.A chelate is a metal ion held by an organic molecule at several points, keeping micronutrients such as iron, zinc and manganese dissolved and available across a wider pH range.Ppm of an element means milligrams of that element per litre of solution (mg/L), the unit nutrient recipes use; it is not the ppm shown on an EC meter.A stock solution is a concentrated nutrient mix, often 100x or 200x final strength, diluted into the reservoir; calcium and sulfate/phosphate stocks must stay separate.Per-element dosing builds a feed from individual salts or single-element stocks so each nutrient can be set independently, such as cutting nitrogen without cutting potassium.
