Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont
You may like the smell of burning leaves, but did you know you were
sending an excellent soil conditioner up in smoke? Instead of burning
leaves or stuffing them in garbage bags for the trash haulers to take
away, compost them.
Compost improves garden soil by increasing its organic matter. This,
in turn, improves soil drainage. Organic matter is especially beneficial
in heavy clay or light, sandy soils. Organic matter reduces soil
crusting and helps soil hold water and nutrients. Decomposing leaves in
your compost or garden feed earthworms and beneficial microbes. Leaves
also supply a small amount of nutrients, including those trace elements
and minerals that trees have mined from deep within the soil. Between 50
and 80 percent of the nutrients that trees extract from the soil end up
in leaves, ready to be recycled when the leaves fall (IF left on the
ground or put into compost).
Microorganisms are what decompose materials to make compost. To do
their work they need carbon sources for food, and nitrogen for proteins.
They are most effective when the ratio of carbon to nitrogen (C:N) is
an average of 30 to one, by weight. You donít need to weigh what you add
to the compost pile, just be aware of approximate amounts that youíre
adding. Generally, two to three parts (by volume) of brown to one part
green materials works well. Some gardeners add an ďactivatorĒ to help
the microorganisms, which provide a source of protein and nitrogen. You
can buy these commercially, or use alfalfa meal from garden or feed
In general, course woody material (sawdust, leaves) is high in
carbon. Moist, dense material (manure, grass clippings, non-meat kitchen
scraps) is high in nitrogen. Too much carbon materials and the compost
pile will decompose slowly. Too much nitrogen and you may smell ammonia
To compost leaves, alternate leaves with layers of soil or manure.
Make layers of leaves six to 12 inches thick, layers of soil or manure
about one inch thick. To hasten decomposition, shred leaves first with a
rotary lawn mower or shredder. Moisten each layer. Finish the compost
pile by slightly rounding the top to help the pile hold water. Cover
with an inch of soil. Some also alternate layers with a sprinkling of
lime and fertilizer. Some leaves such as sugar maple may be more acidic
with a pH of 4.3 and so need lime added, while other leaves such as of
ash have a more neutral pH of around 6.8.
Next, cover the compost pile with plastic. Hold the sides in place
with wire, concrete blocks, or boards. Turn the pile every few weeks
throughout the fall, adding moisture during prolonged dry periods. Both
the plastic (heat) and turning (aeration) will help speed decomposition
and make the final product more uniform. Unless the pile is already
moist, uncover when rain is predicted.
Compost piles are simple to make, but it does take time for the
process to work. If you start a compost pile this fall, don't expect to
use it in the spring. However, it should be ready to spread next fall.
Keep in mind that you are not limited to leaves for composting. You
can use any plant material that's not diseased, doesn't contain mature
weed seeds, and hasn't been treated with pesticides. In addition,
non-meat kitchen scraps can be composted.
Plant materials and products that are easy to compost, and which
generally decompose most rapidly, include egg shells, coffee grounds,
pine needles, fruit peels and rinds, paper, sawdust, straw (not hay, as
hay often contains weed seeds), vegetables, tea bags, wood ash, and wood
shavings. Materials that are slow to decompose and may take two years
to break down include coarse wood chips, branches, corncobs and corn
stalks, and nut shells. Breaking these materials into smaller pieces,
and adding high nitrogen materials will speed up their composting.
If you donít have room or time to compost all those fall leaves, you
can put a pile aside to add to a compost pile when you need brown carbon
material this coming season. Or simply rake the shredded leaves to use
to mulch around perennials and shrubs. Mulch helps conserve moisture
in summer, keeps soils warmer in fall and spring, and reduces frost
heaving in winter. Just donít use too much of this organic mulch (a
couple inches a year is good) or youíll smother your perennials, and
provide a habitat for mice during winter which can chew bark off of
trees and shrubs.
Return to Perry's Perennial Pages: Green Mountain Gardener Articles-- your reliable source of gardening information for over 50 years.