Taking steps to develop a good starting soil should be every gardener's priority, and when it comes to feeding plants nothing beats organic home-made compost. Good compost contains an ideal range of nutrients, which are released slowly and taken up by plants when they need them.
There are times when providing a supplementary feed can give plants a real boost however – when they are fruiting, if they are affected by poor weather or pests, and crucially if they are in containers.
How and what you feed them with is important, especially if you garden organically. Many of us will prefer to avoid using commercial non-organic fertilisers, and opt for organic ones, and fortunately there is a way of making your own organic fertilisers for virtually no cost. We’ll take you through the key steps.
Plant Nutrition Basics
Plants require three main elements for good health:
- Nitrogen (labelled on fertiliser packaging with an N) is for green, leafy growth.
- Phosphorus (P) is for healthy root and shoot growth.
- Potassium (K) is for flowering, fruiting and general hardiness.
Commercial fertilisers, both organic and non-organic, provide these elements in precise amounts – just look carefully at the label to find the NPK ratio. A balanced fertiliser will have an equal ratio (7:7:7 for example), whereas a specialist product, such as one for feeding tomatoes or strawberries, will have a higher potassium (K) content. Ratios will differ between brands, but will be indicated on the packaging as something like 2:2:6.
Different Types of Home-made Fertilizers
There are several different organic fertilizers that you can make yourself.
Comfrey is the wonder plant of the home-made fertiliser world. It grows prolifically in places that many other plants wouldn’t, and contains high levels of all the essential nutrients for plant growth as well as a number of trace elements. There are different varieties of comfrey but the best one to plant is Bocking 14 – it doesn’t self-seed, so it won’t invade your garden.
A popular way to use comfrey is to make a liquid fertiliser:
- Harvest a large bag of leaves. It’s advisable to wear gloves as the hairy leaves can cause a rash.
- Squash them into a large container, preferably with a lid to keep out the smell, and weigh them down.
- Leave for a few weeks, and pour off the liquid into a clearly labelled container, keeping it out of the reach of children.
- When required dilute 15:1 with rainwater. Aim to water the soil rather than the leaves or stems, as fertilisers can cause scorching of foliage.
Stinging nettles are high in nitrogen and can be used in the same way as comfrey to make a liquid feed. You’ll definitely need gloves when working with this plant! Scrunch up the harvested plants and weigh them down in the container. Dilute the liquid as before with rainwater until it looks like a weak tea solution.
Grass clippings can be easily added to a compost pile, but in large quantities often make a slimy mess. They are high in nitrogen and potassium, and can be used as a mulch on your vegetable plot. After a light weeding, apply dry clippings in thin layers which barely cover the surface of the soil. Adding further thin layers at two-week intervals will ensure they break down quickly without going slimy.
Wood ash contains useful amounts of potassium and trace elements, depending on the wood burnt – young wood is better as it contains higher amounts of potassium. It can be added in small quantities to the compost heap, where it can be blended with other materials.
When adding wood ash direct to the soil, it’s best to apply it in autumn or winter so the remaining compounds can break down without causing harm to your plants. Wood ash is alkaline so avoid using it around plants that prefer acidic soil, such as raspberries, or where potatoes will be grown, as alkaline conditions can encourage potato scab.
Using Home-made Fertilisers
When you’ve made your own fertiliser, it’s tempting to use all of that home-grown goodness, and add it liberally to your plot. This should be avoided as it will often do more harm than good – too much nitrogen in particular can cause lots of soft, leafy growth which is susceptible to aphid attack.
Timing is also important. It’s better to add small regular quantities when your plants need it, such as when they are flowering or fruiting, rather than single, large applications.
It’s a good idea to add generous quantities of nutrient-rich compost to your garden and containers in the autumn, top up with mulches which will slowly release nutrients throughout the growing season, and to use liquid feeds for your fruiting crops. The Grow Guides in our Garden Planner provide detailed information on how to grow healthy plants.
Making your own fertilisers is not only good value for money and in most cases free, but it’s also sustainable – using plants from your plot to feed your own veggies!