Gardening – Creating compost

Compost making is one of the most important jobs you can do in gardening. Compost provides organic matter that supports beneficial soil organisms, which in turn suppress or kill soil-borne diseases and make nutrients more available to plants. Plants grown in compost show increased resistance to foliar diseases as well. The compost helps activate disease resistance genes in plants. Compost improves soil structure, water-holding capacity and drainage ability; producing healthier root systems. It also acts as a form of gentle, slow-release fertiliser.

To make a well-balanced compost, layer half and half of dry-woody type material and soft-green type material in a heap. Dust with lime or dolomite every few layers to reduce the acidity. High acidity inhibits some beneficial microorganisms.

More green materials can make the compost hotter, which is good for killing seeds and diseases, but too much green material may make the compost go soggy, anaerobic and smelly. Some examples of green materials include grass clippings, weeds (without seeds), animal manure, green leaves, kitchen scraps, excess fruit (citrus are fine for composting, despite what some people say) onions and seaweed.

Increasing the proportion of woody material will slow the composting down, producing a compost that is better for fruit trees (although still good for veggies as well). Woody materials include tree prunings, plant stalks, wood chips, dry leaves, wood ash, cotton or wool based cloth, sawdust, cardboard and shredded newspaper.

Avoid treated or painted timber, coal ash, dog or cat poo (may contain harmful bacteria and parasites), meat and bones (because these attract rats), glossy paper, synthetic cloth or lint, weeds that survive composting (such as dock roots, canna roots), diseased plants (unless hot composting) and walnut or oak leaves.

Cold composting is the slowest form of composting (three to four months is normal) and isn’t as effective for killing weed seeds or diseases as hot compost  is, but is much less work and produces high-quality compost. To make cold compost, just layer your materials as they come to hand. Use three compost bins if possible; one for building up with new ingredients, one for maturing compost and one for holding mature compost until it is used.

For hot compost, collect the materials separately and combine in one go. Shredding or chopping the material before putting it in the heap will make the composting process faster and hotter. The volume of compost materials should measure at least one cubic metre for maximum effectiveness; any less and the heap won’t get hot enough. Within a few days the centre should reach at least 65C, which is enough to kill most weed seeds, pathogens and nematodes.

Turn the hot compost using a pitchfork to transfer from one pile to the other and mix the sides into the middle as you turn it. Turning the heap keeps it heating, so turn it at least one more time before letting it mature. If necessary, water the heap to keep it moist but not soggy. The temperature will gradually drop until the centre of the pile is barely warm to the touch.

If that all sounds too difficult, then drop in to the Warkworth Rose & Flower Show on the at the Town Hall on November 15, where you can enjoy the glorious results of other gardeners’ hard work.

Andrew Steens