How to improve soil fertility in your garden
The first place to start, if you haven’t already, is to know your soil type. Is it sandy, clay or friable? Find out with the following ‘touch test’. Keep in mind that different areas of your garden may have different types of soil.
- Take a handful of your garden soil and add enough water to it for it to be molded into a ‘ball’.
- If the water runs through really quickly, and the ball doesn’t hold together, it’s sandy.
- If the soil clumps together and gets sticky, it’s clay.
- If your soil is friable, meaning it’s easy for plants and trees to push their roots through, the ball should hold together and be somewhat spongy with no evident sandiness.
In this guide we will make mention of the following terms relating to your soil.
- Top soil, being the strata that you’re mainly planting into, containing organic matter and nutrients. It is a slightly darker colour to the subsoil.
- Subsoil lies beneath the topsoil and is denser.
- Hydrophobic soil, which regardless of soil type, repels water.
- Soil pH, being the measure of the acidity or alkalinity in the soil.
- Soil microorganisms are the bacteria that decomposes organic matter. This will decline in acidic soil.
There are some great hacks you can employ to improve the fertility of your soil if it lacks vital components for growing thriving plants.
The best way to improve any soil is with lashings of compost. If you have clay soil, the compost will loosen it, creating more and larger air spaces while making it better draining. You shouldn’t add sand to this type of soil as you'll end up making concrete! Conversely, if you have sandy soil, compost will make the soil denser, holding more water.
When adding compost, you’ll need to dig down at least a spade’s-depth to lay the topsoil bare for mixing. It’s a good idea to separate the topsoil and subsoil as you remove them so you can replace them in the correct order when you fill the trench or hole back in. This will ensure the airier topsoil retains the many beneficial micro-organisms which live in the strata, which would otherwise die if there’s not enough air at the bottom of the hole. Make sure you have mixed your compost and natural garden soil using a 50/50 ratio. The compost will attract microbes to the roots which are essential for releasing plant nutrients to this area. Consider using superphosphate and bone meal - two external sources of phosphate - which is essential for good root growth and ensures that new plants get off to a good start. Bone meal is also an extra source of calcium for plant growth, but not optimal if you have digging dogs!
The correct soil pH is vital for plant growth as it influences the availability of essential nutrients and affects the activity of soil microorganisms. So if your soil looks sub-par, check the pH to see whether it is suitable or needs to be adjusted. You can do this with a soil pH meter. If the pH of your soil is less than 5.6, it may be too acidic for most plants to grow in. To raise the pH you can add compost and dolomitic lime. If your soil pH is higher than 6.4 you will need to acidify your soil. This may be done by adding ammonium sulphate or acid compost.
If you’re a proponent of ‘no-dig’ gardening, in which you don’t believe in turning the soil, you can lay a thick layer of organic mulch such as peanut husks, bark chips or compost on top of it, letting nature work her magic of sucking all the goodness into the lower levels of the earth. You can also add wood ash (from real wood, not charcoal or coal) which makes a very good amendment to your garden as it’s full of potassium – excellent for flowering and fruiting crops. Just be careful not to use too much as it could add too much alkaline to the soil.
Maintain a permanent mulch of rough compost, straw, bark chips or coir, because as the mulch decomposes, earthworms and other micro-organisms will take the organic matter down into the lower layers of soil which will improve its texture.
Loamy soil is composed mostly of sand, silt, and a smaller amount of clay. If you’re lucky enough to have good loam, you don’t need to overly cultivate the soil, just make sure that you keep it well mulched with organic substances. By doing this you will introduce beneficial micro-organisms into the topsoil. If you have hydrophobic soil, a thick layer of compost mulch will help keep the water where it should be.
Grow ‘green manure’
You can also set about growing your own ‘green manure’ – leguminous crops which biologically fix atmospheric nitrogen and enhance soil fertility. They are ‘soil-builders’ which contain thousands of bacteria which convert nitrogen into nitrates that are soluble and easy for the plant to take up to build plant proteins. Nitrogen is important to all plants as it is the ‘leaf-maker’, and a deficiency will result in poor growth and pest problems. Try growing red clover, peas and beans.
Grow cover crops
You could also incorporate cover crops that have the unique ability to return nutrients to the soil, adding organic matter to the soil while improving the soil structure. The cover crop aerates the soil as the roots grow and die, enhance water availability, and hold onto nutrients better to prevent them from being leached out of the topsoil. Rye, wheat and barley are some used on a larger scale, but mustards, brassicas and borage can be grown at home and dug back into the soil.
Use organic fertilisers
Wherever possible, use organic fertilisers formed out of plant and animal residue. This is the best option if your soil lacks vitality. Bear in mind that fertilisers are a stop-gap measure, and are good for feeding your plants, but not necessarily your soil.
It is easy to cultivate soil that is conducive to growing healthy and thriving plants. With any one of the hacks you can improve your soil fertility today. Just start!