Biostimulants

Amino acids for plants, properly explained

By Joseph Barrington, Founder of Dr Forest · May 2026

What amino acids are doing inside a plant

Twenty proteinogenic amino acids underpin every plant function: enzymes, structural protein, chlorophyll, hormones. Plants synthesise all twenty themselves, starting from the nitrate or ammonium taken up at the roots.

That synthesis costs photosynthetic energy. Nitrate has to be reduced to ammonium, then ammonium incorporated into glutamate via the GS/GOGAT cycle, then transaminated outward into the rest of the amino acid pool. It is the single most energy-expensive piece of plant nitrogen metabolism.

Apply free amino acids directly to leaves or roots and the plant skips that work. The molecules arrive ready to go.

The energy saving alone justifies the input. The four biostimulant effects on top are the reason amino acid hydrolysates are one of the most heavily researched product classes in commercial horticulture.

Four mechanisms, in order of impact

Direct nitrogen delivery

Plants take up amino acids through both root membranes and the leaf cuticle, using dedicated amino acid permeases. Uptake is rapid and the nitrogen is delivered in a form that integrates straight into protein synthesis: no reduction step, no GS/GOGAT bottleneck.

The same molecule also doubles as a carbon source for the plant. You are not just feeding nitrogen, you are feeding a small amount of usable carbon backbone with it.

Chelation of micronutrients

This is the effect most growers underestimate.

An amino acid carries a carboxyl group and an amino group on the same molecule. Both can coordinate to a metal ion, forming a bidentate complex around iron, zinc, manganese, copper or calcium. The complex is small, water-soluble and electrically neutral, which is exactly the form a root membrane will take up.

Three amino acids do this best: glycine (smallest, fastest), glutamic acid and aspartic acid (both carry an extra carboxyl group). Commercial amino-acid chelates of iron and zinc are built on this chemistry.

On alkaline or calcareous soils — anything above pH 7 — most of the iron and zinc in the soil is physically present but chemically locked into oxide and carbonate forms. Amino acids unlock it. Every rock dust, every bone meal, every bit of compost you have spread carries minerals that an amino acid input will help free.

Osmotic and oxidative stress protection

Proline is the gold-standard osmolyte. Under drought, frost or salinity, plants accumulate proline in the cytoplasm to maintain cell turgor and stabilise membrane proteins. It also scavenges reactive oxygen species generated under heat stress.

Glycine betaine plays a parallel role: another small osmolyte that protects enzymes and membranes under stress, and one that plants will synthesise from glycine when supplied.

Plants synthesise their own proline under stress, but the synthesis itself costs metabolic energy at the worst possible moment. Supplying it externally takes that load off.

Rhizosphere and microbial signalling

Free amino acids in the rhizosphere are premium substrate for the bacteria and fungi that surround roots. Short peptides (di- and tripeptides preserved in enzymatic hydrolysates) act as direct signalling molecules in plant–microbe communication, including with arbuscular mycorrhizal fungi.

The downstream effect is the one anyone who feeds biology recognises: more nutrient cycling, more biological disease suppression, healthier soil function.

The L-form rule

Plant enzymes are stereospecific. They recognise and metabolise only the L-form of an amino acid. The D-form is the mirror-image enantiomer — same atoms, opposite geometry — and most plant biochemistry will not bind it. Some D-amino acids are mildly inhibitory to growth.

The hydrolysis method determines the L:D ratio of the finished product.

Enzymatic hydrolysis uses proteases at 40–55°C and neutral pH. Peptide bonds break cleanly, the chiral centres stay intact, and the short bioactive di- and tripeptides survive. Slower and more expensive to run.

Acid hydrolysis uses concentrated HCl at 110°C. Cheap and fast. Roughly half the amino acids racemise to the D-form, peptides are destroyed, and heat-sensitive aminos (tryptophan, cysteine, serine) degrade outright.

Label tells: "enzymatic hydrolysis", "L-amino acids" or "L-form" stated explicitly, free amino acid content above 75%, and a clearly stated protein source. Anything that just says "hydrolysed protein" without specifying any of that is almost certainly acid-hydrolysed, and worth walking away from.

Both Dr Forest amino acid products are enzymatically hydrolysed.

Source matters: what protein, what process

Amino acid biostimulants on the market come from a range of source proteins: animal collagen, soy, alfalfa, sunflower, fish. The source determines the amino acid profile of the finished product. Some are heavy in glycine and proline; others lean on glutamic acid and arginine.

Both Dr Forest amino acid products are made exclusively from plant proteins, enzymatically hydrolysed. No slaughterhouse waste, no animal by-products, vegan. The two formats are built for different jobs.

The concentrated powder, in detail

84.8% total amino acids, with 17 L-type aminos identified individually on the label. The profile is led by leucine (11.72%), aspartic acid (10.31%), valine (8.37%), lysine (7.55%) and glutamic acid (7.29%), with glycine (3.97%) and proline (2.59%) supporting chelation and stress tolerance.

Figure 4 · Amino acid profile

What is in the concentrated powder, by weight

Seven named aminos plus the remaining ten. Gold bars mark the workhorses for chelation and stress tolerance.

Leucineprotein synth

11.72%

Aspartic acidchelator

10.31%

Valineprotein synth

8.37%

Lysineprotein synth

7.55%

Glutamic acidchelator

7.29%

Glycinestrongest chelator

3.97%

Prolinestress osmolyte

2.59%

Ten otherscombined

33.0%

protein-building chelator / stress osmolyte

Total amino acids · 84.8%

Built as a complete biostimulant-fertiliser hybrid: 13-0.3-8 NPK, 3,000 ppm amino-acid-chelated iron (one of the most bioavailable organic iron sources for correcting chlorosis), 500 ppm magnesium, plus humic and fulvic acid. Micro-granules dissolve cleanly into a sprayer, watering can or fertigation line.

If you only buy one amino acid product, this is the one. It handles foliar spray, soil drench, fertigation and seed soak.

The foliar liquid, in detail

23.4% total amino acids, of which 20.9% are in free form, meaning the amino acids exist as individual molecules rather than bound up in peptide chains, and can cross the leaf cuticle without any further breakdown. That 89% free-to-total ratio is unusually high.

Formulated at pH 4.5–5.5, which is the optimal range for amino acid absorption through the leaf. At that pH most amino acids carry no net charge (they exist as zwitterions), making them small, neutral and easy to absorb through the cuticle and stomata. 3.9% nitrogen delivered in amino acid form is the fastest organic nitrogen available for foliar correction.

The right choice for a dedicated foliar programme, fast post-stress recovery sprays, or tank-mixing into another liquid feed to lift the uptake of whatever else is in the tank.

Which one when?

The powder is the higher-concentration multi-method all-rounder. The liquid is the pH-optimised foliar specialist. Running both across a season is the strongest amino acid programme: drench the soil with the powder for biostimulation and the iron / magnesium / humic side, and foliar-spray the liquid for fast-response leaf uptake and tank-mix work.

Rates and timing

Powder: 1–3 g per litre of water, as a foliar spray or root drench. Every 2–4 weeks in active growth.

Liquid: 2–5 ml per litre of water. Same schedule.

Time of day: early morning or late evening for foliar. Stomata are open, transpiration is low, scorch risk is zero.

Tank-mixing: amino acids will chelate the minerals in whatever else is in the spray tank. Adding a small dose (1–2 g of powder, or 1–2 ml of liquid, per litre) into your normal liquid feed reliably improves uptake of the minerals in that feed. This is one of the most useful applications.

One frame to hold onto: amino acid hydrolysates are biostimulants, not fertilisers. They do not replace your base nutrition. They make every other input work harder.

Where this sits in a feeding plan

Amino acid hydrolysates are one of the best-evidenced biostimulant categories in commercial horticulture, and on a cost-per-application basis they are also one of the cheapest. Safe on seedlings, compatible with anything organic, useful at every phase from transplant to flowering.

If you are adding one new input to your routine this season, this is the one.

FAQ

What do amino acids do for plants?

They supply pre-assembled nitrogen the plant can absorb without re-synthesising it from nitrate or ammonium. They chelate locked-up iron, zinc, manganese, copper and calcium into root-available forms. They protect cells under osmotic and oxidative stress, with proline doing most of the work. And they feed rhizosphere microbes and signal to mycorrhizal fungi. A 2022 meta-analysis of 1,000+ open-field trials found protein hydrolysates delivered an average 17.9% yield increase.

What is the difference between the powder and the liquid?

Concentration and application format. The powder is 84.8% total amino acids with 13-0.3-8 NPK and 3,000 ppm chelated iron, built as a multi-method concentrated all-rounder for foliar, soil drench, fertigation and seed soak. The liquid is 23.4% total amino acids with 20.9% in immediately bioavailable free form, formulated at pH 4.5–5.5 for fast foliar absorption, and built as a foliar specialist. Both are enzymatically hydrolysed from plant protein and contain >99% L-form amino acids.

Are amino acids a fertiliser?

They are biostimulants. They enhance the plant's ability to take up and use the nutrients in your base feed, rather than supplying meaningful nutrition themselves. Use them alongside your normal feed, not instead of it.

How often should I apply them?

Every 2–4 weeks during active growth. More frequently around stress events: drought, frost, transplanting, heat waves. The recommended dose is well below burn threshold, so applying more often will not damage anything.

Why does L-form matter?

Plant enzymes are stereospecific and metabolise only L-amino acids. D-form amino acids are chemically identical but built as a mirror image, and plants cannot use them; some are mildly growth-inhibitory. Enzymatic hydrolysis preserves L-form. Acid hydrolysis produces roughly 50/50 L and D. Look for "enzymatic" or "L-amino acids" on the label.

Can I use them on all plants?

Yes. Vegetables, fruit, herbs, ornamentals, lawns, trees. Particularly useful through stress periods and high-demand phases like flowering, fruiting and post-transplant recovery. They will not burn at the recommended rates.

Can I mix them with my other liquid feeds?

Yes, and this is one of the most effective ways to use them. Amino acids chelate the minerals in whatever else is in the tank, which improves uptake of the whole mix. Add 1–2 ml of liquid amino acids per litre to your normal feed.

Can I use them with seaweed or humic acid?

Yes. Amino acid hydrolysates are compatible with seaweed extracts, humic and fulvic acids, and most liquid fertilisers. They enhance absorption of the minerals in those products too.