← Organic fertiliser FAQ

What does organic fertiliser do?

It does two jobs at once: it supplies the nutrients a plant needs, and it feeds the soil organisms that release them. The second job is the one that compounds from season to season.

The nutrients, and what each one is for

Nitrogen builds leaves and stems. A shortage shows first in the older leaves, which go pale and undersized because the plant moves its nitrogen to the new growth. Phosphorus goes into roots, flowering and fruit set. Potassium governs flowering, fruiting, sugars and the plant's water regulation, which is why potassium-led feeds are the standard answer for tomatoes and soft fruit from midsummer onwards.

Then there are the three that general feeds usually omit. Calcium builds firm cell walls. Magnesium sits at the centre of the chlorophyll molecule, so a shortage reads as yellowing between the veins of older leaves while the veins stay green. Sulphur is needed to build proteins. A multi-input blend supplies all six.

What it does to the soil

This is the part that does not show up on the bag. Organic materials leave carbon behind when they break down, and that carbon is what soil bacteria, fungi and worms live on. Over several seasons that builds crumb structure, which lets water in and air through, and raises how much water the soil can hold before it dries out.

None of that happens in one application. It is a slow, cumulative effect, and it is the honest reason to feed this way rather than any claim about the nutrients themselves being superior.

What it does not do

It will not rescue a plant that is short of something this week. Mineralisation takes weeks and slows to almost nothing in cold soil, so a granular feed applied to a struggling plant in April does very little until the ground warms. That is what liquid feeds are for.

It also will not fix a problem that is not a nutrient problem. Yellow leaves are as often waterlogging, drought or root damage as a deficiency, and feeding a plant with sick roots makes nothing better.