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Gardens on the Go - Organic Horticulture

Autumn Leaves

warm days of summer are beginning to wane. Our watering chores begin to decline as days shorten and the nights and days begin to cool. This annual turn of events signals the beginning of the most important time of year for gardeners. We plant and weed, water and feed our gardens, but truly our most important task is to preserve, protect, and build our soil. Mother Nature is a brilliant master gardener. As winter approaches she has devised an ingenious method for preserving the nutrients in the soil and protecting the billions of microorganisms that live there. During the shortening days of autumn she has planned for leaves to drop from deciduous trees and shrubs to cover and protect the soil. A thick coating of leaves provides insulation and protection for beneficial soil creatures, prevents soil compaction, and also slowly releases nutrients as the leaves break down. Leaves insulate the roots of plants against extreme temperature fluctuactions, and help to protect against repeated freezing and thawing of roots. It is a system that has worked for millineum, and is responsible for the tremendous growth of trees and shrubs that blanket much of the earth without ever being watered or fertilized by anyone but nature itself. By leaving these leaves where they fall instead of raking leaves in the name of neatness we are creating an ecosystem that is nutrient rich and full of biological diversity.

Nitrogen is an extremely soluble nutrient, and is easily washed away by our many inches of rain. Consequently our soils here in coastal British Columbia tend to be Nitrogen deficient. Nature’s system for preserving Nitrogen in soils over the winter is quite simple and beautiful. Leaves that fall and begin to decompose actually tie up nitrogen reserves in the soil as the decomposing bacteria use the nitrogen for food energy. Over the winter the leaves may freeze and thaw, and as more and more bacteria and fungi invade the leaves they begin to decompose. Once they have reached the final stages of decomposition, an event that generally coincides with the warming of the soils and the beginning of the gardening year, the bacteria and fungi move towards alternate food sources, and the nitrogen from the leaves is slowly released back into the soil. Even in cases where the leaves are very tough and waxy and don’t completely break down over winter they have still served the purpose of protecting the existing nitrogen in the soil from washing away by absorbing some of the impact of the pounding winter rains. 

Any organic mulch will help protect and improve your garden. Small chipped branches form deciduous trees are very beneficial, and may also result in an increase of ph, (important on the coast where our soils are most often overly acidic), an increase of microbial action, and a decrease of soil borne pests. Do not confuse small chipped wood branch material with straight bark mulch. Bark contains very little nitrogen. Soil organisms must actually rob the soil of nitrogen for the energy needed to help decompose the bark mulch, and decomposition of bark is a very lengthy process. Bark also contains toxins that help protect it against insects and diseases, and these toxins can inhibit many types of beneficial bacteria. Only in specialized ecosystems like virgin old growth forest can plants effectively bark mulch, and even then in limited and balanced quantities, along with rotting wood. Straw can be used as a mulch as well, but avoid hay, as it often contains numerous weed seeds. Take caution that the straw that you use has not been treated with herbicide, as is often the case. 

Remember that our main job as gardeners is to preserve, protect and feed our soil organisms so that they can do their job, which is to feed our plants. If we take care of the soil it will provide nutrients, protect soil water reserves, and maintain the web of soil life that is so crucial to every creature’s existence on this planet. 

 If you want to learn a lot more about the soil and how to protect it you might want to consider taking the Organic Master Gardener Program being offered in Parksville this fall. Your planet will thank you.