Organic matter that can be composted or added to the soil is anything that once was alive and embraces all the following,
1. Garden waste. This will include composted crop waste such as bean and pea stalks, beetroot, parsnips, Hamburg parsley, salsify, scorzonera, carrots, swede, turnip and celeriac tops, potato haulms, tomato, sweet corn, pumpkin, cabbage, Brussel sprouts, purple sprouting broccoli, and kale plants. Compost can include cut flower plants like sweet peas (which are poisonous), dahlias and chrysanthemums. Even poisonous rhubarb leaves can be composted because they certainly are not poisonous to microbes that rot them down very quickly. The prunings of soft fruit and top fruit cut into 5cm pieces. Unwanted wild flowers plants. I compost all weeds regardless of their reputation. However, I think that I would have to dry Japanese knotweed for a few months before adding this to the compost but I would give it a go if I had it on the allotment. With the way that I make compost, sieving it carefully before putting it on top soil, I think that anything that regenerated would quickly be seen and removed. Drying seems to be the best method before composting. Anyway, it would be a very resilient weed that could recover from being turned every two days for over two months. All these sources of organic matter will be decomposed by the compost microbe community.
2. Kitchen waste including all vegetable and fruit peelings, kitchen absorbent paper used to mop up normal spills, coffee and tea dregs, egg shells, bones and corks. Egg shells are calcium phosphate and a little calcium carbonate; the same compounds that are in bones, rock phosphate and limestone all of which contain valuable plant nutrients. The organic matter in eggs comes from the small amount of protein inside the shells.
3. You can use cooked food residues too but it probably be best to put this material in worm bins that can be sealed. I have used sour milk in worm bins together with rancid yoghurt with no noticeable effect except to increase the population of worms. They say that cooked food attracts wildlife like rats but no one has told the rats on my allotment because they infest my compost cooked food or not.
4. Farm waste including animal manures, straw, hay, broken eggs and feathers. If you can get hair, hoof and horn clippings all the better because they contain proteins like keratin and proteins contain the important nutrient nitrogen. Horse stable manure mixed with combings, trimmings and clippings can be put onto the compost heap.
5. Leaves from forest trees and leaf mould even from walnuts. Walnut leaves will contain juglone which will inhibit the growth of plant seedlings. It is noticeable that there are no enormous piles of walnut leaves undecomposed under these trees. This is because juglone is just another organic compound as far as microbes are concerned, which they will eagerly devour. Conifer needles are more of a challenge for microbes to digest because of the phenols in them. However, the specialist decomposers will devour these given sufficient water. Tree leaves can be composted on their own to make leaf mould, a very good soil conditioner and potting compost. However, this does not mean they cannot be used on the general compost heap. They will rot down wherever they are put.
6. Charcoal, although some would say that this is mostly inorganic carbon. I like to marinade it in comfrey liquid and urine for about three months so that it is thoroughly infused with nutrients. It can then be crushed and applied to the soil. I doubt very much that charcoal on its own increases the fertility of the soil.
7. Wood chips and woody shreddings are very valuable compost and mulch materials. When used as a mulch they make the allotment soil surface like the forest floor and introduce many benefits. I am experimenting with woody shreddings as an addition to the compost bins. For years I have been telling people not to add these woody shreddings to the top soil because nitrogen is depleted by micro organisms that decompose them. I'm not so sure now. So I have filled one of the dalek bins with shreddings and will be turning it every two or three days with the other bins. I want to see whether this material will decompose as quickly as some of the other compost ingredients.
8. Organic wastes from industrial processors such as hops, fleece, wool, hoof and horn, blood fish and bone, hair and fish meal.
9. Shredded paper waste and, even better, organic shredded paper waste. I would compost this because it will tend to remove nitrogen from the soil by immobilisation if added in too large amounts.
10. I love card and cellophane. They both rot down so quickly especially the corrugated card. Lots of this brown card has been recycled several times leaving fibres exposed to microbe decomposing enzymes and acids. Card is useful to use as a mulching material under woody shreddings but be prepared for it to rot away quickly.
11. Clothes made from wool, leather and other animal skins, silk, cotton, linen, nettle and hemp. Any clothes made entirely from plant or animal fibres are fine to put onto the compost heap. At the moment I am composting some leather gloves, leather boots, a cotton shirt, woollen socks and woollen trousers. I do not expect them to decompose quickly but they will decompose. Carpets made from jute and wool. Leather shoes, belts, straps, hand bags, saddles and horse tackle will all eventually rot away and form a rich compost.
12. Scum and sludge from gutters and drains preferably composted.
13. Shavings, sawdust, husks, chaff and stubble are best composted because they will immobilise nitrogen in the soil.
14. Urine added to comfrey tea or compost.
15. Guano from birds and bats.
16. Stems, branches and brushwood from shrubs and trees. These can be shredded or used in Hügelkultur beds.
17. Sea weeds are best composted until excess sea salt has been washed out. Shells from the beach, which are mainly calcium carbonate but do contain some protein.
18. Composted bark, cocoa shells, peat and coir.
19. Mushroom compost is mainly very well-rotted horse manure, hay and straw and can be added straight to the vegetable garden soil.
20. Worm compost – although it’s not just worms – and worm tea.
21. Lawn and weed turfs stacked for six to twelve months and then composted or added straight onto the vegetable garden.
22. Lawn mowings which can be added straight onto a well-made compost that is being regularly turned. They rot down very quickly helping other ingredients of the compost to decompose rapidly too. This is probably not because they have more nitrogen in them than any other leaves but because they have been shredded and have a large surface area exposed to bacteria attack.
23. Herb teas such as comfrey, nettle and sweet cicely or mixtures of them.
24. Green manures such as field beans, alfalfa, clover, fenugreek, lupin, field peas and vetch, which will add nitrogen as well as organic matter.
25. Perennial legumes like lupins, laburnum, wisteria, broom, gorse, together with Frankia infected plants like Elaeagnus x ebbingei, which can be used as chop and drop or cut up and put on the compost heap. The exudates and secretions of perennial legumes together with their composted seeds, stems, leaves and branches all will add organic matter and nitrogen to the soil.
26. Cover crops such as mustard, grazing rye, buckwheat, forage radish, turnip, and caliente mustard which will immobilise nutrients over winter and prevent them from being eroded or leached away before they are dug into the soil in the spring.
27. Water butt, pond, stream, lake, canal and river silt are all rich in organic matter but I would still compost them for a while.
28. Vacuum cleaner fluff if you have a woollen carpet and fluff out of washing machines. Vacuum cleaner waste can contain a lot of hair particularly if you have a pet. Hair is mainly keratin which is a protein and relatively high in nitrogen. Dust is primarily very small soil particles and not flecks of skin. However, if it were skin, this too is high in protein and thus nitrogen. Also the flecks of soil particles still contain nutrients and would be a valuable addition to compost heaps. Household sweepings from hard kitchen floors are always worth adding to the compost heap as well.
29. There is a constant rain of leaves, dead twigs, flower buds, flowers and fruit debris from overhead trees that fall onto the allotment throughout the year and all this can be swept up and composted.A rich compost will be made if just a small proportion of this organic matter is used. The diversity of ingredients will be reflected in a varied microbe community and pest and disease suppression due to competition for nutrients and space.