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Composting - April 2015

Why do we need to compost our waste? Why not just put it in the appropriate wheelie bin? The answer is that compost is a major resource in the garden, too valuable to give away. The plants that you grow are only as good as your soil, and the most effective way to improve your soil is to add home-made compost.  The good news is that making compost is pretty simple -  if you put a pile of compostable material together, that is, anything that was once alive, eventually you will get compost. The skill comes in doing it quickly and doing it well.

Traditionally in gardening and agriculture soil is regarded as an inert medium that the plants just anchor themselves into, and the life forms living in it are regarded as pests to be exposed for the birds to eat or sterilised with heat or chemicals. However, it is becoming clear that this really is not the case. Some 25% of the life on earth is in the soil. There are more life forms in one tablespoon of healthy soil than there are people on earth. Healthy soil, an increasingly rare thing, is alive; it's like a miniature rain forest down there, and the vast majority  of these life forms are beneficial or at least neutral to plants.

Here's a way of thinking about the role of these microorganisms. We like to think of ourselves as individual, single organisms, but in reality we are living in symbiosis with millions of bacteria, mainly in our gut. These friendly bacteria break down our food into its component parts, which we can then absorb through the gut wall into our bloodstream. Without them we'd get very poor nutrition no matter how much we ate, which is why antibiotics play havoc with our long-term health. The same situation exists for plants, except that they mainly use fungi, and these fungi are outside of their roots in the soil. The soil is the stomach of the plant, and its microorganisms break down the food contained in the soil into a form that the plant can absorb through the roots. The role of compost is that it's full of these microorganisms as well as food, and it brings your soil to life. This is why home-made compost is so valuable. All bought compost is sterilised to remove weed seeds, and while it adds humus, it won't boost fertility to the same extent as home-made compost.

When you use compost, you don't have to spread it on thick like a mulch. You can use small amounts to 'inoculate' your soil. It's like making home-made yoghurt - take a spoonfull of live yoghurt and add it to a bowl of warm milk, and after a few hours you have a bowl of yoghurt because the friendly bacteria have multiplied in the milk. So it is with compost, add a spade-full to your soil and let the friendly microorganisms turn your soil into something that resembles compost.

The kind of microorganisms in your compost largely depends on how you make the compost. There is hot composting and cold composting. Both have their pros and cons. Hot composting is very fast, possibly as quick as 3 months, and consequently takes up less space (because you only have 3 months' waste around at a time instead of 12). It is largely done by bacteria, which is what generates the heat, and the heat will kill weed seeds, perennial weeds and some fungal diseases. The drawbacks are that you have to be very precise with mixing the contents, and that the compost needs to be turned regularly, so it is quite hard work.

Cold composting is largely  carried out by fungi, and takes a year or more to break down. The fact that it doesn't get very hot means that it doesn't kill weed seeds, but it also doesn't kill the beneficial fungi, and so it is much more alive than hot compost, and particularly alive with life forms that are valuable to plants. It also takes much less skill and labour - you just add materials as you have them available and let it compost in its own time.

Neither method is right or wrong. All of the technical details you read on the subject of composting are referring to hot composting. For hot composting, you need to start off with a suitable bin, like the one below (slightly overstuffed).

This one is 1.3 m square, and you need at least a metre cubed really. Ideally you'd have three in a row, but since this cost £160, I'm saving up for its neighbours. You can make pretty good ones out of three pallets screwed together, with the fourth one removable to get at the compost, and a lid. A tip is to get a couple of extra pallets and dismantle them to fill in the gaps, to stop the compost filling up the centre of the pallet and rotting it more quickly. The lid should not be old carpet, which leaches some nasty chemicals.

You have to compile the heap all in one go, so you have to accumulate enough material to fill the bin, in the right balance of green to brown materials, which is 1 green to 2 brown. Green materials are nitrogen rich, and include kitchen waste, young weeds and grass cuttings. Brown materials are carbon rich materials, such as paper and cardboard, straw, dead leaves and woody stems. Most gardens produce way more green waste, and so it's a good idea to save up cardboard and old newspapers to balance it out. It has to be damp enough, which it probably will be with the right ratio of green waste, and it has to have oxygen, so not too tightly packed.

When you have your materials, you mix them together, fill the bin, and put a lid on. You leave it for 3 weeks or so, during which time the temperature will go up, possibly up to 50+degrees, and then down again, which you can measure with a thermometer if you want to be scientific. Then you take it all out of the bin, mix it up and put it back in. Ideally you would turn it straight into the second bin, filling the first bin up with new material to start again. The turning mixes more oxygen in and ensures that the cooler material at the sides gets mixed in and composted. Then you leave it another 3 weeks or so, during which time it will heat up again and cool down, and then turn it again, ideally into the third bin. One more heat cycle and you should have good usable compost, with two more bin-fulls in progress.

Much slower, and much easier, is cold composting. The dalek type is ideal for this.

You just add stuff as you have it available, and wait until it's composted. You can fill it to the brim and in summer it will mush down in just a few days, to be topped up again. Don't bother trying to use the little trap door, just push the whole thing over and lift off the bin. If you're not that strong, don't leave it too long, because when it's packed full, it's really heavy! Uncomposted material from the top is just used to start it off again. If it gets a bit slimy and full of gnats, add newspaper or cardboard, and if it's too dry and not composting, add more green waste. Practically the only way you can go wrong is with grass cuttings. If you add them in a big lump you're going to make silage not compost. Silage is when farmers mow green grass, just like lawn clippings, and pack them tightly into a concrete silo, covered in plastic and left to ferment anaeobically, like saurkraut. It keeps for a year and the cows love it for their winter feed. So if you pack your grass in tightly so that air can't get it, that's exactly what is going to happen, and after a year you will take the bin off to find a layer of fermented, undecomposed grass cuttings. Try keeping a stack of old newspapers to scrunch up and mix with the grass cuttings to get a better mixture of carbon and nitrogen and more air in it.

The picture below shows my emergency compost heap, when all six of my bins are full to the brim, otherwise known as the 'great wall of compost'. It's not a great way to make compost; it doesn't heat up and the weeds are exposed to light and grow back, but it's better than nothing, and certainly better than giving it away to the council waste scheme - and it will make compost.

You can buy compost activators to speed up composting, but please don't waste your money. Those of you who keep chickens will have realised that chicken poo is a great compost activator, but there is an easier, free and abundant one that is very effective - urine. Obviously this is easier for chaps to accomplish, but you can get a specially adapted watering can for lady gardeners!

It is perfectly safe, and doesn't pong unless you overdo it in summer, and is great for activating compost and feeding the plants. It makes a lot more sense than using clean water to flush it away.

As for the materials you can use, anything that was once alive will compost, including wood and products made from wood, like paper and cardboard. Wood takes a bit of composting though, and can only be broken down by fungi. You need to make sure it is fully composted before using the compost, otherwise it uses up nitrogen from the soil, which takes it from the plants. This is particularly an issue if you use sawdust for animal or chicken bedding. Straw makes better compost, but less good bedding. Old clothes can be composted as long as they are natural fibres, tea bags, cardboard packaging, although look out for some that have a plastic film through the middle, as well as junk mail, as long as it isn't glossy paper, which is largely clay. Don't compost cooked food or animal bones unless you are using a hot bin (see below), and then only if it is really hot, mainly because it attracts rats. Don't worry too much about diseased material, unless it is something super-persistent like onion white rot. There is no evidence that blight survives composting over winter, but it's best to avoid blighted potato tubers just because they can remain intact in the compost. Cut up heavy sticks or large items. A tip is that using a shredder dramatically improves the composting of woody waste.

Rodents can be a problem. Avoid concentrations of food rich items like surplus veg or fruit, as well as cooked food, and keep the heap damp, ideally with urine - it puts them off to be weed on! Or you can put mesh under the bin or stand it on concrete. Failing that, a trap in the top of the bin, as long as the lid is securely on to protect birds, will catch any culprits. Again, a hotbin should help if rodents are a persistent problem.

A hotbin is the latest innovation in composting, combining the best of both worlds. You add compost a little at a time and it heats up to up to 60 degrees, thanks to its superinsulated walls. It also is closed at the bottom, and so keeps rats out. I have only had mine a couple of weeks, and it is only just beginning to warm up, so I can't say much about them. They do take a bit of care in cutting up the ingredients and getting the mix right to make them work. I will update with experience!

That about sums up a beginner's guide to composting. If it seems like a lot of information remember, if it was once alive, it will turn into compost if you just put it in a heap and wait. Apart from a few gnats or a bit of a pong, there is a real limit to how wrong it can go!

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