Composting and Compost Crops

Composting is a great way of building soil fertility and utilizing garden waste.  In a Biointensive system, it's a cornerstone of closed-loop gardening.  In his classic book, How to Grow More Food..., John Jeavons advocated using 60% of your garden space just for compost crops.  My experience as an ecological gardener makes me think that is right.  The more I focused on healthy soil, the more successful my garden.

A compost crop is a crop used to either build soil with its roots or provide biomass for mulch and compost.  I haven't planned my garden to 60% exactly, but I use a rule of thumb that each should be a compost crop 2 of every 3 seasons.  That attention to the soil means I can successfully grow a crop every 3rd season without inputs.

There are lots of methods for composting, and the method you choose or develop is up to you.  If you are new to composting or want to level up your game, there are lots of resources.  It's worth checking out Jeavon's books on composting as part of a system.  I'll describe something like that here for illustration, and then share some context with my compost.

A simple method of making compost is to use four stakes to stake out a  3-4 ft. square  pen to hold your compost.  The bottom layer should be fibrous or woody scraps so that the pile can drain and breathe.  As you harvest green compost materials, layer them to a 6" in the pen and water.  Then use dry compost crops materials as the brown layer of the compost.  That dry material can be left in beds dry or harvested and stored for mulch or compost.  Water between each layer and the pile daily.  Screen and stored the finished compost for use in the garden.

My compost is a more casual affair.  I make piles all over the garden as material becomes available.  We are water challenged in the desert, so unnecessary water use is avoided.  But compost must stay moist enough for the living decomposers to do their work.  I often cover my compost pile with something to protect the pile from the sun and hold the water in.

I rarely have enough material to hot compost, so I cold compost.  I have more space to grow food than I've been using, so building lots of compost is a top priority for me this year.  For this reason, I've been growing lots of cover and compost crops as well.  I know that the roots are breaking up hard soils and feeding the ecology underground by leaking sugars and nutrients as they grow.  That soil community will cycle and share nutrients with my food crop later on.

I use sheet mulching as often as I can.  It is basically composting in the bed itself.  Another similar method is the "Lasagna Garden".  I alternate deep layers of compost materials and layers of brown materials with cardboard or newspaper sandwiching it all in.  I aim for 1' deep mulch, watering between every layer and periodically for 4-6 months.  Then I can start the bed in my rotation plan.

We have a strange relationship with carbon in these modern times.  We clean it off the garden and even pay someone to remove it.  Then we go buy bags of it to use as mulch and in the garden.  Closing the loop means having a different relationship.  Woody carbon material is what fungi thrive on.  When they thrive they connect with roots and share important minerals. 

I process woody scraps down to small size, chipping or lopping apart.  And then I leave all that in a small pile that I wet sometimes to prevent fire hazard.  These and my other piles move around the garden, allowing the compost's drainage to leach into the beds below.  With this practice and by using cover crops my soil was rapidly improved.

Often, folks think of compost as the way to build soil organic matter (SOM).  But it actually isn't very good at that.  It's very hard to add enough compost to make a measureable increase in SOM.  Following soil health principles and using compost crops will be more effective.

But compost is worth its weight in gold by delivering the healthy soil organisms to the garden.  They use SOM as food and grow.  And as they live and die, they deliver usable nutrients and minerals to the plants.  The plants cannot grow at a steady pace and thrive without this community.

I use compost every time I do anything to a bed, just a half inch or what every I have.  I also use as a general fertilizer for repotting plants and side dressing vegetables.  I soak some compost in water to water things that could use the nutrient/organism drink.