Phosphorus, Flavour and the Finish

The Science · Phosphorus

Phosphorus, flavour, and the finish

It is the one nutrient nearly every feed overdoes — and the peer-reviewed work says more of it does nothing for weight or quality, and quietly costs you both.

What the plant needs, and what each feed delivers

A plant draws about 25–30 mg/L of phosphorus from the soil solution — enough for full yield and full quality. Above that there is no gain (Westmoreland & Bugbee 2022); phosphorus simply accumulates and starts locking out zinc and iron. Dr Forest sits on the mark. Two leading living-soil feeds, fed to their own labels on a reused soil, sit well over it.

What the plant needs, and what each feed delivers Phosphorus in the soil solution, mg/L, on a reused soil 25–30 needed 40+ zinc & iron lock out Dr Forest on the mark ~27 mg/L Competitor A ~2× over ~55 mg/L Competitor B ~3× over, deep in lock-out ~78 mg/L

Competitor A and B are two of the UK's leading living-soil feeds; delivered levels are estimated from their own published analyses fed at label rates on a reused soil. The 25–30 mg/L band is from controlled trials.

Phosphorus peaks when you least want it

Phosphorus is slow. Bundle it into the feed and re-amend every grow, and the level in the soil does not hold steady — it climbs, and it is at its highest late in flower and into the finish. That is exactly backwards: a clean, aromatic ripening wants the feed easing off, not a phosphorus peak locking out the micronutrients that carry flavour.

Phosphorus peaks when you least want it Soil-solution phosphorus across a grow, mg/L. A clean finish wants it falling. FINISHING 40+ lock-out 25–30 needed wk 0 wk 2 wk 4 wk 6 wk 8 wk 10 wk 12 A re-amended feed — climbs, and is highest at the finish Dr Forest — held flat at what the flower actually uses You want phosphorus easing off for a clean, flavourful ripening — not peaking as you finish.

What too much phosphorus costs flavour

The damage is not the phosphorus itself — it is what it blocks. Once soil phosphorus climbs past sufficiency it ties up zinc and iron, the two micronutrients most tied to aroma, terpene production and a clean finish. The plant can look well-fed and still taste flat. In controlled trials, raising phosphorus above 25–30 mg/L lifted neither yield nor quality; it raised tissue phosphorus, micronutrient lock-out and leaching instead (Westmoreland & Bugbee 2022; Shiponi & Bernstein 2021).

How Dr Forest holds the line

Phosphorus goes in once, as a slow charge sized to hold the soil at ~27 mg/L — sufficiency, and no higher — then the weekly feed carries only nitrogen, potash, calcium and magnesium. The level stays flat from first week to finish, so zinc and iron stay available and the flavour comes through.

The living soil built on this See the Living Soil programme →
Dr Forest — Made by Growers. Backed by Science.