Master mulching
Ken Thompson is a horticultural scientist and writer who is keen on making his own garden compost to use as mulch
Mulch is simply a layer of something on the soil surface. It can be almost anything, from plastic to gravel, but usually it’s some kind of organic matter, such as garden compost, lawn mowings, chipped bark or shredded prunings. The primary purpose is usually weed control, but an organic mulch will do a lot more than that.
Q Beds always look good with mulch on them, but is it just cosmetic? Absolutely not. A 5cm layer of organic mulch will smother weed seedlings and prevent weed seeds in the soil below from germinating. It also keeps soil moist, so you need to water less often and, as it breaks down, it releases nutrients that will feed your plants. It’s also food for many soil organisms, from fungi to earthworms, which in turn improve the soil structure, which is the key to healthy root growth.
Q What should I use to make mulch?
Start with whatever cheap materials are to hand. This will normally mean things like garden compost or lawn mowings, but a local brewery may be a source of spent hops, and if you live near the coast you may be able to get hold of seaweed (but get permission from the land owner or local council first). Shredded prunings make a good mulch, so if you have hedges, consider investing in a shredder. A local tree surgeon may supply wood chips cheaply, or even for free. Bagged bark mulch from the garden centre is usually the most expensive option.
Q Does mulch have to be ‘well rotted’, and what does that actually mean? ‘Well-rotted’ compost is just compost – before it’s well rotted, it’s not compost, it’s just a collection of raw ingredients: lawn mowings, tea leaves, banana skins and so on. How well rotted it has to be before you use it is up to you. Animal manure (a mixture of faeces, urine and bedding from farms or stables) makes a great mulch, but fresh manure can be smelly and unpleasant to handle, and straw bedding can also contain herbicide residues. Allowing it to rot for at least a couple of months before use solves both problems.
Q How should I apply mulch? Are there any plants that don’t like it? Autumn is the ideal time to apply mulch, after rain and before the ground is chilled by winter, so the soil underneath is moist and still relatively warm. Spring is nearly as good. Robust perennials will readily grow through mulch, but take care not to cover small plants with a thick layer. Also leave a gap around the base of trees and shrubs, to avoid rotting. Always apply mulch to damp soil and top it up as necessary to maintain a thick layer.