Composting: make your own black gold Like the rest of us who garden on clay, they need tons of organic matter to open up the soil structure in their ever-evolving garden. James reckons they've used 15-20 tons of compost this year. He comes from a good compost pedigree, having learnt his system from Prince Charles's garden at Highgrove. To create enough of the lovely stuff, you need some wooden holding bays. James recommends the three-bay system, each bay of equal size, two containing fresh material and a third bay empty. Then bay two is turned into the empty bay three, so that bay one can be turned into bay two. Bin it: Holt Farm uses the bay system for making garden compost At Holt Farm, they are clear on what goes in and what doesn't and aim to add activators (chicken manure, comfrey leaves or nettles) every four weeks. James tells me the key is to keep the whole decomposition process aerobic, and to achieve this, you need to guarantee two things. The first is that the bays must be turned every week (quite a feat if you're doing this by hand). The second, organic straw (from agricultural feed suppliers, or use shredded paper/cardboard), must be added in layers with the garden and kitchen waste, in equal quantities. The straw - which is rich in carbon - helps to keep the balance with the green waste, which is rich in nitrogen. Both these elements are essential to keep the oxygen-loving bacteria alive, which would otherwise suffocate, with smelly anaerobic bacteria then moving in. A note on rats: Cooked food scraps attract vermin, so never add them to the heap. The weekly turning definitely deters rats as they don't like the heat of a regularly turned heap. Rats, mice and even snakes seem to find an anaerobic, ie slightly warm, heap of decaying matter an attractive place to burrow. The compost is ready to use when it is dark brown and crumbly and the original material is no longer recognisable. The heat created as part of the breaking down process will have gone. More good stuff Even easier than this - without the need for very regular turning - is making leafmould, highly relevant this year, with all the trees so laden with foliage. First, make a container with anything to hand that could contain the leaves - a corner of the garden, against a fence, where they won't blow away - or you could put four posts in the ground with chicken wire around them. It is not vital to cover the leaves, but you do need to stop them blowing away. Collect up anything in the garden (bar large branches and evergreen leaves), heap it, water it (dry leaves will just sit there and won't rot down), cover it and leave for 18 months. It's not bacteria that breaks down the dead leaves, but fungi, and the process is slower. Check your heap every so often to make sure it's not bone dry. Even easier, just fill a few bin liners with leaves, make holes in the base and stash them somewhere. It has the same effect and takes about the same time. Spread the joy Leafmould is brilliant for the top-dressing of lawns. It's low in nutrients so won't encourage over-quick growth, and if you mix it with sand, it's easy to rake in after aerating your lawn. In the garden, James also uses leafmould in his potting mixes. He sieves it to get rid of any big lumps and then mixes it according to different recipes. For seed sowing, the low nutrient value of leafmould is ideal, as it doesn't encourage sappy, quick growth in the seedlings. Use half leaf mould, half silver sand. For potting, use four parts leafmould to two parts loam (James obtains his from stacked turves, but sieved top soil is fine) to one part grit. Finally, for a mature plant mix for containers, use: four parts leafmould to five parts loam to four parts garden compost to two parts grit. Soil Association rules do not allow sterilisation of the mix, so at Holt Farm they do get the odd weed seed coming through, but not enough to be a problem. By spring I now aim to have plenty of home-made compost to mulch our one-and-a-half-acre garden, with leafmould also ready in about a year. Yeo Valley organic garden reopens in spring 2013, April 25-end October, 10am-5pm. Entry £5 (01761 461650; theorganicgardens.co.uk). Compost dos and don'ts Do add to the heap All grass clippings Cut flowers Kitchen waste, eg broad bean pods, outside lettuce leaves, peelings Weeds - not those going to seed. Not persistent perennials All cardboard and paper (shredded), but not very heavily inked or glossy Cotton clothes Don't add to the heap Cooked food - it encourages rats and flies Citrus - bake on a low heat in the oven and then use as firelighters instead Egg shells - too slow to break down Coarse bark - too slow to break down Wood shavings - most are treated with preservatives, so best avoided Perennial weed roots - they will start to grow and invade the whole heap Plants which have gone to seed - they will just shed all their seed into the heap and germinate when you spread the compost Anything diseased - e.g. wood infected with honey fungus or courgettes with mildew - this will encourage fungal spread Man-made fabric - will not decompose Reader offer: Buy a traditional-style compost bin made from pressure-treated FSC wooden slats with an optional cover. Guaranteed for 15 years against rot. Available in small, medium and large, the medium size bin measures 93cm wide x 93cm deep x 70cm high and holds approx 448 litres of compost. On offer at £39.99, RRP £69.99, a £30 saving. Optional cover £14.99. All prices plus £4.99 p & p. Delivery within 21 days. Visit gardenshop.telegraph.co.uk/compostbox