Sunday, July 20, 2014

The Joy of Compost

Left corner: my first compost pile, 1972
One of the joys of being a home gardener is the participation in the cycle of life, from starting seeds to recycling all that garden produce into compost.  What is compost?  The product of the breakdown of organic materials by microbes. Composting has become a major industrial method of disposing of unwanted organic materials.  It can take on a highly technical aspect.  But home composting by gardeners is to industrial composting as home vegetable gardens are to corn monoculture.  In the home garden, it not only disposes of old leaves and overripe squash, but makes a lovely product that enhances soil and plant productivity. Soil scientists all concur that addition of organic material is the universal cure-all for soils (except peaty or "muck" soils, which are almost entirely organic matter).  Finished compost is high in humus, which alters the physical characteristics of soil for better nutrient availability and water percolation.

Compost can be used in many different ways.  It can and should be dug into the soil at planting.  It can be mixed with garden soil for potting purposes.  It is a very successful topdressing around established plants. When applied to the soil surface, it will be integrated into the soil over time and create a more friable soil.  In the shorter term, it makes an attractive mulch and will help to retard weed establishment.
Compost used as mulch

Note that they are empty.
There are as many ways to make a home composting operation as there are to make homemade lasagna.  I knew a gardener who made little chickenwire cages (about a foot wide and a couple of feet high) that were hidden behind shrubs.  She put garden scraps in those over time, then forgot about them.  A year later she took apart the wire to harvest a tiny pile of compost.  Some people make a huge heap of everything in the back corner and then turn it over once a year to get at the decomposed part. Others buy a plastic compost container or even a compost tumbler.  (I suspect that these often fall into disuse.)  Many gardening books and articles show elaborate constructions of three wooden bins. I've never understood how this can be successfully managed. They should not be regarded as necessary to home composting.

The system I use is cheap and flexible.  It is ordinary wire garden fencing made into temporary bins. (For people of average height, about 4 feet high works well.)  In the fall the bins can be expanded to hold fallen leaves, and as the new growing season begins, the fencing is wrapped more tightly into smaller bins.  They are not anchored and the bins can even be rolled up tightly for storage.  The compost can be turned frequently (a compost pitchfork is best) and the area can be raked in between uses.

What has to be achieved in a home compost pile is to allow the plant materials to decompose rapidly without excessive odor.  Woody materials must be run through a shredder if they are to be added. Other plant parts will benefit from cutting into smaller lengths or chopping by hand into pieces (squash or other large fruit or tubers).  Roots will not usually compost.  Don't add diseased plants to a home compost pile, and no really weedy material that has seed pods. I strongly suggest that plant material is all that should ever go into the pile.  No animal parts.  Definitely no animal feces, including manure (that can be composted separately).  In this comprehensive study of compost odors you'll note that the really bad stinks (those characteristic of putrefaction) derive from animal sources.  Ammonia is a common problem in home compost piles (from degradation of high-nitrogen tissues like grass clippings) and fatty acids like butyric acid (detectable at low concentrations!) are noticeable when anaerobic bacteria take over (too wet, too little oxygen).  It helps to understand that a compost pile is a little ecosystem. For details, here is this overview of microbial succession, but the point is that different bacteria and actinomycetes come and go through the process and the system needs to support them.  In a very real sense, what you have is a fermentation reactor and like such a reactor, you need to have the proper substrate and environmental conditions to make it work.

Moisture:  The mixture should not be too wet (so it needs good drainage) or too dry.  If it is too wet, anaerobic conditions result and you will get odor and clumping.  If too dry, the pile won't work and you may even see blue or green mold, a bad sign.  Often plant materials are sufficiently wet, but a sprinkle with a watering can between layers is usually a good idea.
Oxygen:  Aeration is critical.  The beneficial microbes involved in composting are engaged in active metabolism and will use up the available oxygen quickly.  Then the process will shut down.  This is why commercial composting operations turn the compost in windrows daily.  Turning the pile at least once every couple of weeks during active composting is a good idea, and good exercise too.
Temperature: It is perfectly okay to add materials to a compost pile when it is cold, but don't expect anything.  The pile will operate best within a range of  120-140° F internal temperature and the air temperature will affect that.  The process will be most active in summer temperatures.  If the pile is kept moist and turned frequently when it has the right nutrients, it should be at least pleasantly warm in the center.
Layer the "greens and browns".
Nutrients:  A mixture of high-carbon (fall leaves, straw) and high-nitrogen (green plant material) is needed.  Too much nitrogen, you'll get ammonia.  Too little, nothing happens. It is not necessary to be too precise about this, except that too many grass clippings really will be hard to manage.  It is better to add continuously than to store green material.

All this effort occurs fairly automatically during the gardening year.  You'll notice that after a time, the total volume has been reduced and new material is not decomposing very fast.  This is a good time to quit adding material.  Turn a pile once more, adding moisture, then let it sit.  By the fall, you should have compost.

Finished compost
The compost can be stored over the winter in its bins.  (Be wary of leaving it for too long under trees, especially maples - their roots will grow up into it.)  If you have perennial beds, they will appreciate a nice topdressing before winter.  Finished compost should not look like any of its original constituents, but partially finished compost (leaves still discernable) can still be used as mulch.  If you have a garden storage area, try keeping finished compost in buckets or trash bins over the winter.  It'll be usable in the spring before an outside bin has thawed.

If you want to have an even finer texture for the finished compost (to use, for example, in a potting medium, or as part of a fertilizer mixture), it can be put through a riddle.  This will remove odd bits of twig and bark.

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