Turn Those Fall Leaves Into Soil Enriching Compost

Leaves are falling now, covering lawns and yards with carpets of brown, gold, yellow, red and orange. For some gardeners, fall means a lot of extra work in raking up and disposing of the fallen leaves. Others see the leaves as a great source of material for the compost pile, a way of recycling a valuable resource.

If you're interested in making your own compost, the perfect time to start is in fall. A light covering of leaves on the surface of your lawn can simply be shredded with your lawn mower and left in place. They will decompose rapidly and add valuable nitrogen and organic matter to the soil. Once the leaf layer becomes too thick, you must begin raking them up for your compost pile.

Some gardeners simply pile the leaves in one place and allow the composting process to proceed slowly. However, if you want finished compost quickly, you'll want to use the “rapid” or  “hot” composting method. Rapid or hot compost is made by manipulating the decay process, which is done by balancing food, water and air in the compost pile to favor the growth of high temperature microorganisms. A byproduct of their activity is heat.

A hot compost pile can heat rapidly to 120 to 150 degrees F. At these temperatures, most weed seeds and disease organisms are killed, while many beneficial microbes are not.  Once the hot phase is completed and the material cools, lower temperature microbes  and creatures such as earthworms complete the composting process.

To construct a hot compost pile, you will need a combination of bulking materials and  energy materials. Bulking materials, sometimes called “brown materials,” are dry, porous resources such as sawdust, wood chips or straw. They help aerate the compost pile but are too low in moisture and nutrients to decay quickly on their own.

Energy materials, sometimes called “green materials,” include grass clippings, fresh animal manures, fruit and vegetable waste and garden trimmings. These materials  provide the nitrogen and carbon compounds needed for fast microbial growth. If piled without bulking materials, energy materials are too wet and dense to allow adequate air into the compost pile. Such materials may emit a rotten egg smell as they decompose.

Some resources have both energy and bulking material properties. Examples are ground up tree and shrub branches, horse manure and bedding and deciduous tree leaves. These materials will compost readily by themselves and can be added to an existing pile to ensure rapid composting.

To build a rapid compost pile, combine two parts by volume bulking materials with one part energy materials. Some other hints for a rapid compost pile include:

• Chop your raw materials into small pieces.  For best rapid composting, the  particles should be from 1/8 to 1/2  inch in diameter.
• Mix the types of raw materials, rather than layering them.
• A large pile holds heat better than a small pile; for rapid composting, make the initial pile at least a cubic yard (36” X 36” X 36”) in volume.
• Keep the pile moist, but not wet.
• Turn the pile once a week to aerate it.

The raw materials that you use in composting have their own microorganisms. There is no need to add starters or soil. If the rapid process is working properly, you can have ready to use compost in as short a time as 3 weeks. Even if it doesn't work that fast, you will still eventually have a valuable compost that you can use to enrich your garden soil.

Still have questions about composting? 

Sign up for our Composting Basics class!

When: November 24, 2020 6-7:30 p.m. PST.
Where: on Zoom.
How: http://ucanr.edu/compost/2020 sign up by Nov 24 at 4 p.m. to receive a link sent the morning of the class.
Instructors: Master Gardeners Terry Pellegrini and Heidi Aufdermaur.

And remember, all classes are recorded so you can always watch it again later.

Hope to see you there!

Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.