The Mediterranean Gardener

You really can NEVER have enough garden compost; it makes such a difference to soil fertility and the success of your garden, especially in a dry climate where soils are usually poor and very low in organic matter (the sun destroys organic matter in the soil where the soil is exposed to it). I love making garden compost, it’s like making gold dust. It has the strange effect of improving both drainage and water retention in clay by breaking up the very fine particles within and also of increasing water retention in poor sandy soils.

Repeated yearly applications of garden compost will break up even the most sticky clay, although this is an exceptionally large task.  In the garden at South of France hotel I have been able to the convert one 30 m2 area of previously sticky clay into a friable soil but it took the entire contents of the compost heap from the 2 acre garden.  33 giant wheelbarrow loads were rotavated in to a depth of 1m.  4 years later the soil is lovely and friable, however i don’t feel like repeating this process elsewhere!   Plant growth is marvellous in this area and drought tolerance is exceptional.

Garden compost forked into the planting hole is also another good way of breaking up soil and will allow the plant to establish much more quickly.

There is so much very impractical advice about how to make garden compost. Compost making is not a precise thing and in the end there are many ways of achieving success. Compost is an intermediate breakdown product of organic material, produced by the action of micro and other organisms. Any organic material will breakdown to form compost, some of it will be very slow to breakdown (such as wood) and some of it very quick (such as grass clippings).

Garden compost will eventually turn into humus, a largely inert black glue like material – after countless organisms have fed on it.  Whole communities will chomp their way through organic matter, each group feeding on the remains of the last.  Their bodies will trap nutrients and as these too decompose, nutrients will be released to plants. What an amazing system has evolved to feed on and nourish plant life, no wonder it took 4.5 billion years.

Where are you going to get it from? Apart from buying it in, which due to expense will not be feasible in anything but a small garden, you will absolutely have to make your own. This is a very simple and pleasurable process. The perfect end result is a sweet smelling, friable, dark brown, almost crumbly mass which is a joy to work with. However, any garden compost or organic material is better than none and I would have no hesitation in adding even fairly lumpy or slightly smelly compost to the soil.

As garden compost is such a precious commodity, use it on plants and areas that benefit from it most. Tough drought tolerant plants such as lavenders, rosemaries, teucrium, cacti and succulents are perfectly capable of growing in un-improved soil. Better to use it where you want to encourage flowers and lusher growth – herbaceous perennials, roses, annuals, tropicals etc.

Rules for Making Garden Compost (picture left our compost heap after annual Autumn tidy-up)

Ideally you will start with a mix of 1/3 green material (lawn clippings, prunings from containers, kitchen waste etc.) and 2/3 woody/brown material (autumn or winter prunings or autumn leaves). The reason for this is that there is a good balance of nitrogen containing material (green) with lignin-rich carbon based material (brown).There seems to be a vogue for keeping leaves separately to make leaf mould, I find this unnecessary since they rot in the heap anyway. In practice you will have to make compost with what you have as you have as it is available; this will affect the outcome of the compost.

Garden compost will make much more quickly if you shred the material with a machine or by hand with shears. I shred ours with an electric shredder and if you do this you can take nearly all the shreddings and apply it directly to the soil as a mulch without composting it. It will self-compost and disappear very quickly, worms will drag it into the soil. Personally I prefer to compost it as I spread the spent caps of wine pressings on the garden as a mulch every autumn.

It is perfectly possible to make garden compost with unshredded material as long as it is not too tough and thick – it will just take a little longer. Indeed I never pass trimmings of perennial grasses through the shredder as they simply jam it up and they still break down quickly as long as they are kept damp.

You can add anything of organic origin to the heap and it will rot – even food, bread, meat, vegetable oil, fat etc., BUT if you do this you will attract vermin to the heap as rodents will eat even rotting food and it will also attract flies. Better to throw it away – vermin can get into anything that you can buy or make.

You may also add 100% natural fibre clothes and these will rot fairly easily. However you will end up with unrotted buttons, zips, washing labels, nylon thread etc and the clothes will make the heap hard to turn. I gave up doing this as it is too much bother.

Feathers, eggshells, the contents of hoovers (all natural fibre carpets only) and animal manure can also be added and break down quickly to make garden compost.

Cardboard and paper can also be added but they must be shredded as they otherwise form hard dry mats in the heap. Personally I send these to recycling instead.

Older gardening books suggest to add woodfire ashes to keep the heap ‘sweet’.  Of course then fires were very common to heat houses and this was a useful way of dealing with the ashes.  If you have ashes then by all means add them, but never add coal ashes. They are quite alkaline and will neutralise the acidity produced during the rotting process.

It is not necessary to add worms and the like to the compost heap, indeed I have never even seen a worm in my compost heap, although there will be a lot where the garden compost is added to soil (by the way a good garden compost heap will be swarming with invertebrate life, big fat grubs of various types, – some of which are quite disgusting –  countless swarms of woodlice, millipedes, etc.  Do not worry about this, it is a sign that all is well, indeed they are all processing the vegetable matter into garden compost by eating it and excreting the digested remains)

You can choose whether to have the heap housed in a commercial bin, in a purpose built container or simply free-from. It helps aesthetics rather than the composting process to house the garden compost heap in something. If you have small garden, a heap can be hard to hide and a commercial bin will disguise it. Other wise, just knock 4 posts into the ground using fence posts to create a rectangle of the desired size and staple gun chicken wire around them, leaving one side open and the base open to the ground. House it somewhere where access is easy but it is hidden, behind a fence, large shrubs etc. A larger construction will require wooden planks to be nailed to the posts to provide stability.

Preferably all the material is added to the heap together and then the composting process starts with the heap heating up as bacteria break down green matter. If you are lucky enough to be able to make a heap like this, then you should turn it after the heap cools down. A further heat up will occur and then you can re-turn it again, after which a shorter heat-up will occur. If the heap is very large then a further turning can be done.  In practise you will add material gradually and sporadically to the heap and if so the intital heating up may not happen at all.

Some people have several heaps in different stages of composting, but I find it easier to just have one. The organic matter from the winter clean-up gets added to it from November, spring/summer material added the following year and it is ready as garden compost the following October. Anything that is not composted by then I just drag off and use to start the next one.

Add sprinklings of soil to the heap, say every 20 cm of depth to add those essential micro-organisms.

Cover the heap with an old carpet, or ground cover sheet, weighted with bricks at the corners. This will keep it dry,  protect it from inclement weather and retain the intial heat.

Check the heap every 2 weeks; if it is dry, water it. If it is wet fork it up to add air. If the heap is very large this can be a very tough job. Large heaps also tend to get dry centres, to mitigate this make a hole in the centre of the heap and soak water into it.

Composting is mostly a summer process, little will happen over the winter. However there is plenty of time during summer for compost to be produced.

It is not necessary to keep it for 2 years before using it, it will break down in the soil in a flash even after 3-6 months.

Possible Problems

The heap is dry – water it and check it more often; it should be like a tightly rung out dish cloth. Here, I have to soak it every 2 weeks as it drys out very quickly.

The heap is very slow to rot even if moist– there is not enough nitrogenous material. Fork in animal manure (this can be very difficult to get hold of in towns or here where there are very few animals) or water in a source of inorganic nitrogen. For a small heap a handful of ammonium sulphate dissolved in a bucket of water should do the trick. Keen organic gardens use their own urine and there are those who use composting toilets.

The heap is smelly, slimy and attracts insects – there is too much nitrogenous material. Fork the heap over regularly to add air, which will reduce the smelliness and help keep the heap dry. Next time try to add more woody material to correct the imbalance.

The heap contains well rotted parts but others are dry and unrotted. Fork it over more often and shred the material before you add it.

Remember, no compost is ever harmful, even a partly or not very well well rotted one. It will all be a wonderful addition to your soil.

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