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By Island County Extension Agent, Donald B. Meehan
RAISED BED GARDENING ON WHIDBEY
When I started writing this column I thought it would be a good place for some of our county's WSU-Master Gardeners to get in a word or two. So it is today. Veteran WSU-Master Gardener, Bob Alway, allowed me to twist his arm into writing a piece on Raised Bed Gardening. This subject has drawn my interest for some time now. Bob has been using the raised bed gardening method from the time he began gardening. I think you will find his remarks very useful and persuasive. Here they are.
Raised beds are best on Whidbey Island because of our glacially-derived soils and the Pacific Northwest maritime climate.
A raised bed's chief virtue is improved soil structure. This is the arrangement of soil particles--sand, silt, clay--aggregated into shapes with distinct sizes and to the amount of pore space between them.
Whether your soil is too sandy, dry and infertile, or, in a few places, too clayey, draining poorly and hard to work, you can improve it. It is not a complicated process. It takes only soil amended with organic matter--vegetal and animal--to develop optimal garden soil, soil that is friable (mellow), fertile (rich), not compacted. It will be aerated, hold moisture well and provide unimpeded root growth.
Incidentally, a soil amendment is a substance which does not add appreciable quantities of plant nutriments (not nutrients), but improves the soil by modifying its physical properties.
Raised beds are ancient knowledge. For 5,000 years the Chinese have used bed gardening. 2,000 years ago the Greeks noted that plants thrived on the loose soil of landslides. Planting above land level has been the solution when water or soil problems made gardening difficult.
Row gardening is a legacy from Jethro Tull who invented the seed drill and horse-hoe husbandry in the 1700's. Human and animal foot-traffic, as well as the weight of mechanical equipment on each side of the planting rows compacts the soil, destroying soil structure, decreasing aeration, drainage and optimum conditions for plant root growth and functions.
Organic matter is an essential component of raised beds. It is the fundamental constituent of the biologic activity of the soil. Soil microorganisms--bacteria and fungi--are the vital element in the conversion of organic matter to humus/compost. Soil microorganisms require moisture, air and warmth. Temperatures should be over 45 degrees F., preferably 50 to 90 degrees, which are hard to get in our climate. Clear or black plastic over the soil raises the soil temperature several degrees above the ambient temperature, as much as 10 degrees higher on a sunny, windless day. The bacteria need nitrogen for growth. Few organic materials have enough nitrogen to support their own rapid decomposition. A synthetic or organic nitrogen fertilizer may be added.
Organic matter is the secret of most successful gardens. It improves soil structures; binds sandy soil and breaks up clay; makes it more easily tilled; facilitates root growth; makes it less subject to erosion; improves aeration, water penetration and moisture retention; and functions to adjust soil acidity. Humic acids, formed in its decay, dissolve soil minerals making them available. They are cementing agents, coating and preserving the soil crumbs which are the purveyors of nutriments to root tips and rootlets.
How do you make a raised bed? First make sure the soil has a moisture level suitable for cultivating (Squeeze Test). Take up a hand full of soil and squeeze it into a lump. Drop it and if it falls apart, or crumbles easily, it is dry enough to be worked. A raised bed can be free-standing or encased in boards or masonry. Mark off an area for cultivation or tilling several feet wider than the intended width of the bed(s). The width should allow you to reach the bed center from either side. For longer beds, make a cross-walk every 16 to 20 feet, 18-24 inches wide or so, for side-by-side beds.
Till the area with a spading fork, spade or a rear-tined roto-tiller. Rent, don't buy, the latter because you won't need it to maintain raised beds. Till as deeply as possible. Ten to twelve inches is possible with a spading fork. Do not walk on the tilled bed area, "Never, Ever!".
On a free-standing bed, taper the sides so they don't collapse. This adds one to two and a half feet to the total width used, varying with the bed height above land level and the angle of the taper.
Encased beds can be done with old railroad ties or 2-inch thick lumber, 6 to 12 inches wide. It is best to pre-treat with copper or zinc naphthenate (Cuprinol) to deter wood decay. 2" X 10" or 12" can be capped to provide a "bench" to sit on, if desire.
Organic matter should be spread on top of the bed. 8 cubic feet/100 square feet will provide a one inch layer to be worked into the top 6 to 8 inches of the bed, and 1 to 2 cups of dolomite lime and 1 pound of urea or 1/2 pound of ammonium sulfate will facilitate the breakdown of the added organic matter.
There are many variations in making raised beds, but the results are almost invariably good.
Maintenance of raised beds is not much work but is desirable. An annual addition of compost or other organic matter (1/2 an inch or more) should be added. A cover crop in the fall, cut off and turned in the spring helps add organic matter. Do a "Squeeze Test" before cultivating in the spring. Loosen the bed with a spading fork, 12 inches down, rock forward and backward, move back 4 to 6 inches, standing on a plywood "digging board" to prevent compaction.
Prepare your raised bed for seeding. Keep in mind the recommended between-plant spacing. Cross-bed rows waste space but they can be best used by shifting the planting in alternate rows one half space. This keeps each plant or seed equi-distant from its nearest neighbors.
Raised beds are best: They speed up spring planting; are warmer and dryer early; avoid water-logging and soil compaction; are easier to care for; have greater productivity per square foot than the same amount in rows. They establish an area in which a gardener can effectively meet plant's needs. There is no need to purchase a tiller.
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