Garden guru: A new leaf

Good compost requires layering of carbon rich and nitrogen rich garden wastes. Photo / Supplied

With stacks of leaves sitting around, May is that month we most often take notice of the compost bin, only to find it full of summer's grass clippings, with precious little room for more.

It's a crime to even think of throwing such a valuable commodity as leaves away, or hopelessly trying to blow them back under the hedges, King Canute fashion, as if you have the power to stop them from trickling back out all over the lawn as soon as a breeze gets up.

But a great stack of anything is just what you don't need for good compost - whether it's prunings in winter, grass clippings in summer or those leaves right now - a glut is a recipe for compost disaster, as indigestible to the micro-organisms that beaver away within its four walls as making a 5-year-old attempt to down a supersize Big Mac and the bucket of milkshake that comes with it.

A compost heap shouldn't be the place you pile stuff anyway - it should be a thing of beauty, built layer upon layer from carefully selected ingredients like a club sandwich. Twiggy brown stuff rich in carbon - twigs, dead leaves and shredded paper - should be alternated with layers of green stuff rich in nitrogen - grass clippings, weeds and peelings from the kitchen.

What you don't want is something off-balance, akin to a custard slice with a sliver of pastry on the bottom, a drizzle of icing on top and a great wedge of cold gelatinous custard in the middle which oozes out over your shoe when you bite into it.

The custardy-mess trap we most often fall into is to add too many grass clippings in one go. Clippings look for all the world like they will be caviar to our composting worms, and they are - but imagine yourself locked in a room for six months with a 20 ton mountain of caviar and nothing else to eat and you would rapidly crave a bit of bread or a cracker to help the medicine go down.

Worms are the same - and all the other composting moulds and beasties which we can't see but which do all the hard slog. They all need crackerish, fibrous material plus air and a moist but not too soggy place to do their job.

Stacks of grass just sink down into a wet, airless mass which festers and smells to high heaven. The trouble is that gardens today often have lots of lawn but precious few flower beds.

The craze for low-maintenance has removed the seasonal staples like perennials, bulbs and annuals which you once trimmed, cut down and deadheaded, providing plenty of varied material to mix in with all the grass. The rise of vegetable gardening has helped keep the compost balance, and we are getting better at recycling kitchen waste, too.

A chipper is a great addition to the garden if you produce lots of shrubs to prune and hedges to trim. Woody material cut up fine is perfect compost fodder, but inevitably you will still have to put a good deal of your grass in the dustbin or use it as a thin mulch under shrubs so you can concentrate on making compost of quality, not quantity.

Thank goodness then for autumn and a harvest of carbon-rich leaves which work so well layered with grass to keep air in the heap.

Stockpiling leaves beside the compost heap rather than loading them in is the way to go. Make room for a leaf cage beside your compost - four posts and a bit of chicken wire will do the job in half an hour - or bag them up in plastic sacks with a few holes punched in for drainage. Then you can feed them slowly into the compost through the year or just allow them to rot down on their own to produce friable leaf mould.

COMPOST TIPS

* Compost heaps have an enormous appetite for waste if fed in the right way. Use thin layers of a wide variety of biodegradable materials.

* Strips of newspaper and cardboard are a great source of carbon - rich compost fuel but avoid glossy magazines and the contents of office paper shredders.

* Coffee grinds and teabags are great but avoid cooked foods especially meats which will attract vermin.

* The odd shovel-full of garden soil will help activate the heap as the soil micro-organisms drive the composting process.

* Cover your heap with a lid or piece of carpet in winter to protect it from getting too wet. Also water in dry summers to give your decomposers the warm, moist conditions they love.