Ammonium is the cation NH4+, a form of nitrogen plants can absorb directly and use without first reducing it. Its uptake releases hydrogen ions from the root, so it acidifies the root zone. Inside the plant it must be assimilated quickly, because free ammonium is toxic at high levels.
In practice
Mineral feeds usually keep ammonium to a small fraction of total N, often around 10-20% or lessbeing reviewed. That share offsets the upward pH drift caused by nitrate uptake. Saloner and Bernstein found that high NH4/NO3 ratios reduced cannabinoids, terpenoids and yield in medical cannabis. Ammonium excess shows as dark, cupped or clawed leaves and poor root growth, and it competes with calcium, magnesium and potassium uptake.
Lab reports may give NH4-N (nitrogen only): 1 mg/L NH4-N = 1.29 mg/L NH4+.
Don't confuse with
- Ammonia (NH3): the uncharged gas, more toxic, favoured at high pH.
- Nitrate: the main hydro N form, which pushes pH up.
- Urea: an organic N compound converted to ammonium by an enzyme.
The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.pH drift is the gradual rise or fall of a nutrient solution's pH between adjustments, driven mainly by which ions the roots take up.Nitrate (NO3-) is the main form of nitrogen in hydroponic and soilless feeds; its uptake tends to push root-zone pH upward.A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.Medical and adult-use cannabis are separate legal channels: medical access depends on authorisation by a health professional, adult-use on age alone.A COA (certificate of analysis) is a lab's signed report of what it measured in a specific sample, such as cannabinoids, terpenes, moisture and contaminants, with methods and limits.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.Urea is a 46% nitrogen organic compound that soil enzymes convert to ammonium; it is cheap in field fertilisers but a poor choice for hydroponic cannabis.Nitrogen (N) is the macronutrient plants use most, built into proteins, chlorophyll and nucleic acids; it drives leaf and stem growth and is fully mobile.Monoammonium phosphate (MAP, NH4H2PO4) supplies about 12% nitrogen as ammonium and 26.6% phosphorus, adding P while gently acidifying the root zone.Ammonium nitrate (NH4NO3) is a 34-35% nitrogen salt, half ammonium and half nitrate, used in small amounts to steer root-zone pH in hydro.
