Posted: Sunday, October 5, 2008 12:00 am
The inevitability of winter rainfall adds a poignant note to our typically mild, bright and glorious Western Oregon autumns.
Savvy area gardeners savor every moment, delighting in the eye-popping shades of tangerine, purple, butter yellow and scarlet that transform deciduous trees, shrubs and perennials.
This grand finale is Mother Nature's last big show before plants are finally allowed to rest and rejuvenate over the coming season.
Although you can't see it, plants do some of their most important work during the weeks they lie dormant. Living off food reserves stored over the summer, everything from grasses to bulbs to trees turn their energy toward root growth.
This gives any plant put into the ground right now several months (and plenty of rainfall) in which to transfer those all-important photosynthesized sugars straight down into what will become - by spring - an amazingly robust and extensive root system.
When these fall-planted specimens are ready to get going in the spring, this underground support system encourages growth that is dramatically ahead of similarly-sized specimens popped into the border next spring.
Fall is also a prime time to improve soil structure and your soil's inherent ability to withstand what climate experts are predicting: warmer, drier summers and wetter winters.
This very topic is discussed in the fall issue of "The Savvy Gardener," a e-mail newsletter produced by the Saving Water Partnership, a group of Seattle-area utilities that fund water conservation programs in King County, Wash.
Environmental scientist and planner David McDonald, featured in the newsletter, works with professional, builders and citizens to create more sustainable urban landscapes. He says that home gardeners can create their own version of super soil: healthy dirt that can also be part of a broader solution to global climate change.
Here are some of McDonald's thoughts, with thanks to Seattle Public Utilities and newsletter editor Liz Fikejs:
Question: "What does soil have to do with climate change?"
Answer: The soil here on Earth is a huge "carbon sink," storing even more carbon than the oceans. Even in a giant old-growth forest, there's more carbon stored in the soil than in the trees.
A teaspoon of healthy soil may contain four billion individual organisms: bacteria, fungi, etc. This soil life stores carbon dioxide (the most important greenhouse gas), which is drawn from the atmosphere.
Q: "Can my soil-building practices at home make a difference?"
A: Yes! When yard and food wastes are composted at home or sent away to be composted through the city or county, we're keeping carbon-rich organic material out of the landfill.
In landfills, organic materials break down "anaerobically" (without oxygen) and release methane and nitrous oxides - both potent greenhouse gases - to the atmosphere.
Composting, however, allows these organic materials to break down "aerobically" (with oxygen). Very little methane is created using this method.
When you use compost, soil organisms store much of the carbon dioxide as organic matter. Even more carbon dioxide is captured by the abundant plant growth.
This kind of soil improvement reduces the need for fertilizers and pesticides, which generate additional greenhouse gases during their manufacturing process.
Q: "What can I do to build my soil?"
A: Here are a few ideas. Some many not work for your situation, so pick those that best fit your needs:
n When planting an area, dig or till two to four inches of compost into the upper six to eight inches of soil. Don't just add compost to planting holes - that could limit root growth.
n Mulch your garden and beds! Use two to three inches of fall leaves, grass clippings, wood chips or compost to prevent winter weeds and build the soil for next summer. Fall leaves are free, and they make great mulch. Use them as is, run them through a shredder, or mow over them to make finer mulch.
n Top-dress your lawn with compost. Spread up to a half-inch of compost on the lawn by scattering it with a shovel, then rake it into the grass to build the soil. Aerating (pulling plugs with a machine) before top-dressing will help the compost get deeper into the soil.
n If you fertilize your lawn, do it now. Look for the words "natural organic" on the fertilizer bag to get one that's safe for our waterways and good for building soil.
n Start a new bed for next year by "sheet composting." To turn a lawn area into a new planting bed for next spring, start by laying brown cardboard or six sheets of newspaper on the grass, then cover it with eight to 12 inches of grass clippings, fall leaves or any compostable material (or just compost). For a better appearance, you can top this "sheet compost" with wood chips or some other mulch. Wet the sheet compost layers well and let the earthworms and other soil life go to work. By May, you can plant shrubs through the compost, or till the whole bed and then plant.
To learn more, visit the Savvy Gardener website at: www.savingwater.org/savvygardener.