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How to grow organic fertilisers that'll nourish your veggie garden (and you)

Edible gardening guru Jane Griffiths explains why organic fertilisers make for healthy plants, and healthy people too

11 July 2021 - 00:02 By Jane Griffiths
A delicious harvest from a fertile garden.
A delicious harvest from a fertile garden.
Image: Jane Griffiths

As organic gardeners we emulate nature. However, in many ways we are working against a plant's natural instinct.

In the wild, plants return their hard-grown fruit and roots back to the soil, in a continual cycle of growth and decay. In our vegetable gardens, because we eat the harvests, we are responsible for completing the cycle by replacing the nutrients we remove.

Jane Griffiths adds compost to the surface of her beds.
Jane Griffiths adds compost to the surface of her beds.
Image: Keith Knowlton

Adding compost and manure regularly to the surface of the soil will supply plenty of nutrients, but when gardening intensively and trying to grow the maximum amount in a small space, we need something more. This is where organic fertilisers come in.


Plants absorb nutrients once they've broken down to their elemental form. There is no difference between an element originating from your compost pile and one from a chemical fertiliser factory. So why should we use organic rather than chemical fertilisers?

Chemical fertilisers were developed after World War 2, when the US was left with surplus ammonium nitrate, the main ingredient for explosives. It's also a good source of nitrogen for plants, and redundant munitions plants were turned into fertiliser factories. In the space of a few decades, simple farming grew quickly into massive agribusinesses, increasingly dominated by a powerful chemical industry.

Research showed three main elements were needed to improve plant growth: nitrogen (N), phosphorus (P) and potassium (K). So this is what the fertiliser manufacturers concentrated on. However, further research showed more than 60 trace elements in plants. And of these, 16 are essential for growth. Plants were pulling these out of the soil, but they were not being replaced. With increased use of chemical fertilisers containing only the “big three”, the soil in our gardens and farms was steadily stripped of micronutrients.

Today, we'd have to eat 26 apples to get the same amount of nutrients that a 1914 apple supplied. That is what chemical fertilisers have done to our soil

These trace elements are equally important for humans, and if the plants don't contain them then we don't acquire them either. An apple a day keeps the doctor away, right? That phrase was coined in 1914. Today, we'd have to eat 26 apples to get the same amount of nutrients that a 1914 apple supplied. That is what chemical fertilisers have done to our soil.

There is another reason not to use these fertilisers. They are highly concentrated and water-soluble, meaning plants are forced to take up the nutrients — whether needed or not — because they are dissolved in the soil water. Plants are designed to absorb just the right amount of nutrients for optimum growth. When they absorb too many, it results in an unnatural growth spurt. All you see is luscious leafy growth, but insects see a bug buffet. And it is far too much for them to eat, so they invite all their friends to join them — and soon you have a pest infestation.


Organic fertilisers (both liquid and solid) are derived from living things (such as blood, manure, fish, seaweed and bone), and contain all 16 essential elements, plus many more.

Liquid ones are concentrated and need to be diluted — it's better to feed weak solutions more often than a rich feed infrequently. Apply them to the soil as a drench or use as foliar spray (a quick solution to help a struggling plant, or to give newly transplanted seedlings a boost).

Solid organic fertilisers are large organic compounds which, when added to the soil, are broken down slowly into their components. They emulate the natural process by providing a slow and steady supply of nutrients.

Solid organic fertilisers provide a slow and steady supply of nutrients to the soil.
Solid organic fertilisers provide a slow and steady supply of nutrients to the soil.
Image: Keith Knowlton

A well-balanced organic fertiliser needs to be applied once every four to six months, either by sprinkling on the surface of the beds (top dressing) or incorporating it into the top layer of soil around the plants (side dressing).

It can also be placed into the planting holes before transplanting, providing a food source directly where the roots grow.

Always water fertilisers in well after applying.


Instead of buying fertilisers, try growing your own nutritious fertiliser plants that gather and accumulate diverse nutrients from the soil.

These include comfrey, yarrow, alfalfa, borage, buckwheat, clover, dandelion, mustard, nettles, vetch and wheat. Many of them have deep roots which extract nutrients from way below the reach of our vegetables' roots.

To get the benefit of these nutrient-rich plants, use the leaves as mulch or add them to the compost.

Other options are:

  • Green manure: sow thickly and when lush and leafy chop them down. Leave roots in the soil and chop stems and leaves finely. Turn these into the top layer of the soil.
  • Fertiliser tea: chop leaves into a bucket, add boiling water and leave to rot for about a month. Strain, dilute liquid 10:1 and use as a soil drench or foliar spray.

Griffiths is the author of four popular vegetable gardening books, the latest being 'Jane's Delicious A-Z Of Herbs'. Visit janesdeliciousshop.co.za