Plants are like humans. They need a bit of sunlight, some water, a nice place to live and they definitely need food. Unlike humans, plants don’t take to a gourmet menu or a spot of takeaway Chinese. Their requirements are simpler than that, so simple that you can break it down into just three letters: N, P and K.

For vegetables and herbs, nitrogen (N), phosphorous (P) and potassium (K) is the Holy Grail. Some vegetables require a higher proportion of one mineral to another, but generally, a good overall mix is enough to keep them happy and healthy. All gardeners agree with this; they disagree on the type of fertiliser. It all depends on whether you fly the flag for Camp Chemical – or Camp Organic.

The Importance of Minerals

• Nitrogen – this is the single largest constituent of the Earth’s atmosphere and a major element in the creation of amino acids. Animals and plants can’t absorb it whilst it is still in the atmosphere – it has to be “fixed” by bacteria. The bacteria swap a compound that converts the nitrogen to proteins, and the nitrogen gives sugar to the bacteria in the process. Plants need nitrogen for leaf growth.

• Phosphorous – Every time you light a match or watch a firework explode, you’re looking at phosphorous. It ignites on contact with air and so isn’t present in the atmosphere, but is bound to minerals in the earth. Phosphorous helps the plants’ roots to develop.

• Potassium – Potassium in the form of potash is necessary to strengthen plants against disease and poor soil conditions. It naturally occurs in seawater and as part of other minerals.

The Importance of Organics

Chemical fertilisers – the so-called “superphosphates” – were the wondrous invention of the late Victorian era. They promised higher yields and greater resistance to disease and initially they delivered. Unfortunately, once the chemicals enter the soil, they start to strip more nutrients than they put in and lead to heavy metal pollution. Even lengthy fallow periods fail to cleanse the soil.

Chemicals can also over-fertilise the plants and leave them weak and ironically prone to new strains of disease. Organic fertilisers work in harmony with the plants’ ecosystem and nourish the soil. The simplest form of fertilisation comes from plant decomposition, where minerals leech out into the soil as the plant decays and breaks down. New plants spring up and the cycle begins again.

You don’t even have to trot off to your local gardening centre to buy organic fertilisers, as there are cheaper and even free alternatives.

• Manure – the summer isn’t complete without the smell of well-rotted horse poo, which is rich in nitrogen. Most stables and racecourses are happy to donate a bucket or two, and your plants will shoot up.

• Worm castings – worm castings contain essential plant minerals, so if you have a wormery for your composting make sure you take advantage of the faecal matter.

• Seaweed – rich in nitrogen and potassium thoroughly wash collected seaweed and then dry it and grind it into a powder before sprinkling on the soil.

• Green manure – you can buy huge bags of fenugreek and mustard seeds in Taj for just over a pound. Cover the soil liberally with the seeds in the autumn and by the spring, the plants will rot down into the soil. Green manures have bacterial nodules on their roots, which fix nitrogen in the soil and make a perfect no-dig method of fertilising.

• Nettles and Comfrey - both grow wild in gardens and by the side of the road and are technically weeds. Out of all the organic fertilisers, these two stand far above the rest. Gather the plants – use gloves for the nettles – and put them into a large bucket filled about halfway with water. Weigh the leaves and stems down with a brick and pop on a lid. After about three to four weeks, you’ll have a foul-smelling concentrated liquid that you dilute one part to ten with water. Watch your tomatoes grow!