Boosting Organic Matter

Organic matter is gardening gold dust. Lay it on thick and you will be rewarded with happier, healthier plants and greater biodiversity. Add some today! Read on to find out why and how.

What is organic matter?

Organic matter (aka humus) is rotten dead stuff. In nature, fallen leaves, dead plants and animals rot down to create organic matter but many gardens go without due to our habit of raking, sweeping and tidying.

Organic matter really is a gardening magic bullet.

• It helps soil hold onto moisture (like a sponge)

• provides nutrients to plants

• supports beneficial soil life (insects, microbes)

• helps dense, clay soils (common in London) drain more freely

• helps sandy, free draining soils retain water

• may reduce pests and diseases by attracting beneficial life

• helps soils to lock in carbon

• can reduce flooding by absorbing rainfall

• provides nutrients to plants more slowly and effectively than liquid or powdered plant foods which can dissolve into water courses, harming aquatic life.

Adding organic matter

Take the opportunity to dig plenty into your soil when you are preparing beds or borders for planting. You can also spread a thick (8 cm) layer over your soil as a 'mulch' in spring or autumn. This will break down and be incorporated over time with the help of worms and micro-organisms. Do this every year or two to keep soil topped up with the good stuff. Just make sure to avoid it actually touching your plants.

Available in bags from garden centres as soil improver or manure, once rotted it is lovely stuff - dry, crumbly and not (particularly) smelly. Even better you can use your own homemade compost.

Which type to choose?

Soil improver

If in doubt, buy yourself some soil improver (aka soil conditioner). This is commercially produced compost, available in good garden centres and made from rotted kitchen and garden waste collected by local councils (amongst other things). It is not too rich and is perfect for annuals or perennials that don't want high nutrient levels (which can cause them to grow leaves at the expense of flowers).

Manure

The high nutrient levels in manure make it good for hungry plants like trees, shrubs, fruit and veg growing. Readily available in bags but also 'pick your own' from stables. If you get hold of the fresh stuff, pile it up or add it to a compost heap to rot down until dark, crumbly and 'sweet' smelling.

Home made compost

Home made compost has the great benefit of being free, low mileage and reducing your waste output. Nutrient levels will vary depending on your compost ingredients and process, but it is generally nutritious and great for fruit/veg growing. Home made compost is not sterile, unlike commercially produced versions, and may contain weed seeds so be prepared for some hoeing.

Leaf mould

Fallen leaves are best left out of the compost heap as they can slow down the composting process. Let them rot down on their own, however, and the result is a lovely dark, crumbly, homemade soil improver. Simply collect leaves in a strong bin bag or old compost sack, make holes in the bottom for drainage and spray with a little water. Then forget about it for 2 years. Hey presto - black magic. It has little or no nutrient value, but you can chuck down a handful of chicken manure pellets for hungry plants.

Used multi-purpose compost

Multi purpose is intended for growing plants in pots, rather than improving garden soils. Light and fibrous, it is less effective at adding bulk, but can still help so using it as a mulch is better than throwing it away. I do this with all the add 'spent' compost leftover from pots and window boxes. Do look out for any pests and diseases that occasionaly occur in pots (like vine weevil grubs that look like little white maggots), and dispose of compost you spot any.

Bark mulch

Bark rots slowly and, spread as a thick layer over soil, helps to stop weeds growing and reduce water evaporation. It is low in nutrients, and not a quick fix, but will help keep organic matter levels topped up over time.