Mineral soils are typically 1-5% organic matter under natural circumstances. Natural peat soils, on the other hand, develop in waterlogged conditions and are dominated by organic matter – it can make up more than 50% of the soil.
The organic matter content is the easiest thing to change about your soil. Adding organic matter has an almost magical effect, whatever your soil type. If you have a free-draining sandy or silty soil that contains few nutrients then adding organic matter will help it retain water and add in nutrients, without removing the benefits a sandy soil brings.
Clay soils can bake solid in dry heat, and form giant cracks that make it very hard to re-wet. Adding organic matter can help stop that happening, and make your soil less heavy to dig. Organic matter also helps clay soils become more free-draining and less prone to water-logging. Organic matter is what feeds the microorganisms and many of the mini-beasts that live in the soil and keep it healthy, and it helps to protect the soil structure.
There are plenty of ways to add organic matter to your soil. If you have a source of farmyard manure then you can compost it and then dig it in or spread it over the surface. In more urban locations you can make and use your own compost. Surface mulches of organic materials will slowly rot down and add organic matter to the soil, although you do have to be a little bit careful that they don’t create nutrient deficiencies as they do so (if they do these can be corrected by extra feeding – see Chapter 3).
It’s very hard to add too much organic matter to your soil, especially in an urban environment where the amount of compost you can make (and the amount of mulch you can get your hands on) is limited – so be generous. The benefits of doing so are enormous.
If you are concerned that your soil is mineral-poor then you can buy rock dust and add a layer of that each year as a soil improver. This is perhaps more likely to be an issue in soils that have been heavily-cropped for a long time, and you should bear in mind that rock dust is a by-product of the mining industry and is not a renewable resource.
And if you have soil that appears lifeless (probably as a result of chemical use or some other serious abuse) then dosing it with EM or compost tea could kick-start a new soil web ecosystem, but the long term solution is still to add plenty of organic matter for those organisms to eat.
Historically, peat has been recommended for use as a soil improver. Its organic matter content can improve soil, but there’s no reason to use it – there are plenty of other sources of organic matter (many of which are free) that do a better job. Although peat has a dark colour and can make soil look very rich, it actually contains very few nutrients and so is adding nothing to the soil in that way.
If you want a low-fertility soil improver then recycle spent potting compost or make your own leaf mould. If you want something with nutrients then rotted manure or mature garden compost are the ideal choices. We’ll be looking at those (and other options) in more detail in the final chapter of the book.
Another way to improve your soil is to grow plants to do it for you. Green manures are crops grown specifically to improve the soil or provide abundant material for mulches or composting. Different plants have different benefits, so it’s important to choose the right one for your situation. Start by deciding when you want to sow your green manure, as different plants are used in spring (into summer) or autumn. Click on the links to take you to my articles on green manures.
You can follow a traditional soil preparation program to get your soil ready for planting. Depending on your soil type, you may need to dig in winter and leave soil bare to be broken down by winter weather. A lighter dig in spring then allows you to create the fine texture you’d need for a seed bed. Lighter soils may simply be dug in spring, to incorporate any soil amendments. Weeds are removed as you go along, and hoed off as they appear when plants are growing. You may even choose to double dig, which involves digging out the topsoil and then digging over the subsoil layer before replacing the topsoil – it’s important not to mix the two together, which will degrade your topsoil.
The No Dig Garden at Garden Organic Ryton, in June 2006
Or you can follow the No Dig method, where you remove any perennial weeds and then prevent annual weed growth by keeping soil covered with plants or mulches. Soil amendments are left on the surface and allowed to incorporate into the soil by the natural actions of soil organisms. Done properly, No Dig gardening can generate a very healthy soil with few weeds problems and no requirement to dig – an ideal choice for many people.
The idea behind soil preparation is to make your topsoil as inviting a place for plant growth as it can possibly be. Weeds and stones need to be removed. If you are sowing seeds then they need a fine layer to grow into – in a No Dig system it’s the one time when the mulch is removed to show bare soil. This can lead to weed growth, and the solution is to use a stale seedbed technique. You get your seedbed ready, and then leave it alone for two weeks. Any weed seeds close enough to the surface will germinate, and can be removed or hoed off – removing much of the potential for weed growth. Seeds sown now have a very good chance of germinating without being smothered by weeds.
This is the end of chapter 4 (of 6). Chapter 5 looks at some of the more specialist garden uses for peat, and how to avoid them, and Chapter 6 is ‘The Pantry’ – a glossary and peat-free ingredient reference section. Don’t forget to leave your comments and suggestions here, email them to me or come and find me on Twitter and Facebook to have a conversation.