Sorting your stuff

The lists opposite are a reminder of most of the sorts of things that you might want to compost, divided into (1) soft, nitrogen-rich, (2) moderately nitrogen-rich, and (3) tough, carbon-rich material. Bearing in mind the ideal C:N ratio of 30 for composting, a heap made entirely of rich stuff will have too much nitrogen and one entirely of tough stuff will have too little, so always try to mix the two.

Rich stuff (C:N ratio of 5–25) Annual weeds, coffee

grounds, comfrey, feathers, general kitchen waste, hair, lawn

mowings, nettles, old cut flowers, pigeon manure, pond weed,

poultry manure (raw or pelleted), seaweed, pure wool or silk

clothing (shredded), soft, green garden waste, urine.

Middling stuff (C:N ratio of 25–50) Brassica and other

fibrous, green stems, citrus skins, cotton rags, eggshells

(rich in calcium), soiled bedding from hamsters, rabbits,

guinea pigs (not dog or cat litter), spent hop waste, tea bags,

used potting compost, vacuum cleanings (but not if you have

synthetic carpets), waste from distilling, well-rotted cow/

horse/pig/sheep manure, wool shoddy, young hedge clippings

and soft prunings.

Tough stuff (C:N ratio of 50–600) Bracken, cardboard,

corn cobs (crushed), hay or straw, leaves of broad-leaved trees

and shrubs, leaves of conifers, nutshells, paper, sawdust,

tough hedge clippings, waxed paper, wood ash (rich in

potash), wood shavings, woody prunings.

what else can you use?

The principal goal of composting is to recycle organic matter on the spot, without the awful waste

of energy involved in moving it around the country first. Therefore, imported materials should not be added routinely to the compost heap. On the other hand, if there are local sources of composting ingredients that are available cheaply, or perhaps even free, it would be foolish to ignore them.

If your organic waste goes to a local composting scheme, it will be composted at a high temperature under controlled conditions. The resulting compost will be a clean, safe, weed-free material that can be bought and used straightaway in the garden. However, in common with other commercial soil conditioners that are based on recycled garden or forestry waste, it tends to be slightly alkaline, so is not suitable for use around rhododendrons or other acid-loving plants.

Strawy stable manure

can go straight on the garden,

while chicken manure is high in nutrients and makes an excellent

compost activator. Pigeon manure, often available even in the

centre of big cities, is similar.

Many other sources of organic matter are useful if available locally, including bracken, sawdust, seaweed, spent hop waste and mushroom compost, and straw. All these can go straight on the garden as a mulch and will help to improve the soil structure. Bear in mind, however, that in terms of nutrient content and other properties, these materials are very different.

Points to ponder

• mushroom compost is alkaline

• dead bracken, sawdust, and straw contain virtually no nutrients

• material from farms may have had pesticides used on them: always check and, if it has, compost it well before putting it on the garden

• landowners are often happy for you to collect bracken, but always ask first

• collect only loose seaweed washed up by the tide – do not, whatever you do, remove live seaweed from rocks

Active ingredients

Compost activators are materials intended to make up some deficiency – usually of nitrogen – in the compost heap. Some proprietary compost activators claim to contain micro-organisms, but there should be plenty of these in the compost heap anyway.

Direct contact between your heap and the soil will speed up colonization of the heap by bacteria and soil animals. To be absolutely sure, add a spadeful of soil or compost from an existing heap. Cheapest and best of all activators is human urine, applied directly or diluted and added via a watering can.

Something all activators contain is nitrogen. However, if you follow the high-fibre method, your heap will already have the right carbon:nitrogen (C:N) ratio and no extra nitrogen will be required. If your compost heap does contain too much nitrogen, the excess will simply be broken down and lost as gaseous nitrogen or – worse still – as ammonia, causing a nasty smell.

However, if you are composting low-nitrogen material such as hedge prunings or autumn leaves, extra nitrogen will probably speed things up. We’ll consider the best way to add this when we look at the practicalities of making compost. As we’ve seen, many compost materials that lack nitrogen are also low in calcium, and some proprietary activators do contain garden lime. Again, the high-fibre heap doesn’t require extra calcium, but the breakdown of naturally acidic materials like woody waste, autumn leaves, and (especially) conifer prunings will be accelerated by the addition of lime.

Good activators Ammonium sulphate (cheapest option); comfrey leaves or liquid feed made from comfrey (organic); dried blood (organic); lime (ground limestone); nettle leaves; fresh or pelleted poultry manure (organic); proprietary activator; spadeful of soil or compost; urine.

Woody garden wa ste

Larger yards, especially those with long hedges, can generate huge quantities of woody waste.

We’ll consider what to do with it later, but why is it a particular problem?

First, prunings, hedge trimmings, and woody material generally have a high C:N ratio, so they are high in carbon and low in nitrogen. This in itself slows down decomposition, but that’s

only half the problem. The other half is that cellulose is only one of the carbon-rich materials in plants. Another, which may make up 20–30 percent of wood, is lignin. Lignin’s chief disadvantage is that composting bacteria are not good at breaking it down. Second, woody waste has much bigger stems than green waste, so it has a low surface area compared to its volume. This doesn’t give bacteria and other organisms much to work on.

The third problem is the exact opposite of that afflicting a pile of grass mowings, which collapses and runs out of air. A pile of raw prunings, by contrast, contains far too much air, and dries out too quickly. For some gardeners, these problems seem so intractable that composting doesn’t look like a serious option. But

don’t worry,

there are plenty of environmentally friendly ways to deal with even a mountain of woody prunings

Tricky stuff

Some types of garden waste require caution. One of the undoubted virtues of “hot” composting is that weed seeds and pathogens are killed. But traditional, hot composting is hard to achieve in the average garden, so what do we do with such problematic ingredients? Fungal and bacterial pathogens are the worst, but we do need to keep a sense of perspective.

Pests and diseases that live on leaves and stems don’t enjoy life in the compost pile, so you don’t need to lose much sleep over them. Mildew and black spot are unlikely to survive a long spell

in the average compost pile. On the other hand, most soil pests are quite at home in the pile, and are all too likely to survive and be spread around the garden, as are overwintering diseases. There really is no alternative to keeping material with these problems out of the compost pile.

Not very satisfactory solutions are to burn them or bury them in an unused corner of the garden. It’s better to add them to a habitat pile, a heap of miscellaneous woody waste intended

primarily to provide a wildlife habitat.

When looking at the examples listed opposite, bear in mind that they are for guidance only: no list could possibly be complete, and most available advice on what can be safely composted

is anecdotal and contradictory. Also, the longer a pile is left, the smaller the chance that anything horrible will survive. And last but not least, beneficial microbes in mature garden compost are quite effective at controlling many common diseases. But,

if in doubt, leave it out.

What goes in Material damaged by aphids, black spot, brown rot on fruits, canker, gray mold, leaf miners, leaf mites, mildews, potato blight, sawfly larvae.

What stays out Material that might harbor carrot or cabbage root fly pupae, clubroot of brassicas, eelworms and their eggs, honey fungus, pests that overwinter in soil such as pear midge grubs, root rots of beans and peas, rusts, and viral diseases.

From your garden

All normal green garden waste can be composted—after all, disposing of such material is one of the main reasons for composting in the first place. Nearly all of it can go on the compost pile without any treatment, but tough stuff like brassica stalks should first be chopped up, or smashed, with a club hammer or spade. The same goes for tough kitchen waste such as corn cobs.

What about weed seeds? Well, they are not such a serious problem. Even a classic, hot compost pile never achieved a 100 percent kill, so gardeners have always had to live with weed seeds in compost. Of course, the best defense is vigilance in the first place, so that weeds end up on the compost pile before they get around to setting seed.

Also, keep a lookout for weeds growing near the pile itself, or even on it. Trials at the Royal Horticultural Society in the UK suggest that most of the weed seeds found in an open compost pile were not there at the start, but blew in while the pile was rotting down.

From your house

Most types of paper and cardboard make excellent compost

ingredients. Large quantities of flat paper should be avoided, and

in any case are more suitable for conventional recycling. However,

such materials may be used in moderation if you are short of other

types of waste paper—printing inks no longer contain toxic

heavy metals.

Better for compost are those types of paper that are harder

to recycle, such as used tissues and cereal boxes. Birthdays are

bonanza times for the serious composter, with all that wrapping

paper. Cardboard with laminated plastic should be avoided: the

cardboard will compost okay, but you will have the annoying job

of fishing the plastic out of the finished compost.

And if you’re alarmed by media stories of identity theft and

are worried about what to do with all those old bank statements

and credit-card bills, here’s the perfect solution—compost them.

What goes in Cardboard packaging, egg cartons, old

greeting cards, shredded documents, toilet-paper rolls, used

tissues and kitchen towels, waxed paper, wrapping paper.

What stays out Laminated cardboard such as juice and

milk cartons, large quantities of newspaper, telephone

directories, very shiny magazines.