Thursday, March 27, 2008

Raised Beds-It's Spring!

Raised beds in the garden, not the bedroom.

The simplest and most inexpensive way to make raised vegetable beds is to cultivate and rake soil up into a mounded shape. This type of “bed” should in no way be considered a raised bed made by the cultivation method often referred to as the French intensive-biodynamic raised bed. See John Jeavons classic—How to Grow More Vegetables: Than You Ever Thought Possible on Less Land Than You Can Imagine. The methods outlined by Jeavons produces a proper mound of slightly-raised soil and offers the best way to improve the tilth and fertility of your soil.

Many gardeners, however, prefer to construct formal raised beds framed within masonry, plastic, or wooden sides. These sides retain the soil while imparting order and efficiency to the kitchen garden and helping to define it. Formal raised beds also provide a number of other advantages:

 Enhanced drainage for better growth.
 Soil which warms slightly sooner in the spring.
 Sides which help keep soil or mulch from spilling into paths.
 A structure which allows wire mesh to be added to the bottom of a bed to exclude tunneling pests such as moles, gophers, and hedgehogs. However, It’s obvious that carrots prefer a deep soil (as shown to the left) with good tilth and drainage, free of rocks and obstructions that can produce deformities. In less than ideal soils, cultivate as deeply as possible before seeding. Carrots are best grown in double-dug beds with vigilant trapping of gophers, or in boxes raised 24 inches above the soil line and constructed with wire bottoms to deter gophers or other underground gnawing pests. (The root system of a carrot is taken from my new book Roots Demystified, Change Your Gardening Habits to Help Roots Thrive. The grid is one-foot square.) This shows that in a deep soil carrots are able to grow nearly eight feet deep and five feet wide!. This means that even a 24-inch raised be leaves plenty of roots for vegetarian gophers to feast on. This illustrates why extra water and nutrients are needed to satisfy a normally vast root system. (Click on the image to get a clear, detailed view of the illustration as it appears in the book.)

When building garden boxes, line the bottoms with one-half-inch aviary wire, which comes in four-foot-wide rolls. One-inch chicken wire, while less expensive, may allow baby gophers to sneak inside the box. The aviary wire also has more galvanized metal and lasts longer in the ground. Even with this protective barrier in place, the taproot and many other roots will be eaten at the bottom edge of the wire.

 The Cadillac version is to use one-quarter-inch hardware cloth because it doesn’t rust through as quickly.
 When preparing beds for planting, be sure to work the soil with a spading fork to crack open the soil before building the box. After the soil is in, use a flat-bottomed spade so you don’t damage the wire.
 A way that pathways between beds can be cleaned and tended without disturbing plantings.

Raised beds also have certain limitations or drawbacks:

 A formal raised bed with solid sides will cost more and require more time and effort to construct than a simple mounded bed.
 Some gardeners find the angular geometry of the raised-bed structures unaesthetic. (Beds can, however, be masked by perennial plantings or low evergreen hedges.)
 When watering a raised bed with drip irrigation, extra effort must be made to bring the water supply into the bed unobtrusively.

There are many materials which can be used to construct a raised bed. Each has its own unique mixture of attributes and imperfections:

Used Bricks (Recycled)
 Very good looking; construction has character when first built.
 Since bricks are fairly narrow, the finished wall doesn’t take up excess garden space.
 Wire mesh is easily added to the bottom.
 Uses recycled materials.

 Expensive if new.
 Requires some masonry skill or practice to construct.
 In areas where the ground freezes, requires a poured concrete base.

Cinder Blocks

 Wide enough to sit on while gardening.
 If unmortared, easier to work with than brick.
 Can be built on a base of packed gravel
 Easy to add wire-mesh bottom .

 Not easily found as recycled material.
 Best used only for square and rectangular beds.
 Thick blocks take up garden space
 Looks gray and “industrial,” like concrete.
 The large holes in the blocks, usually placed facing up, tend to fill with mulch and soil from the bed.
 Unless mortar and a concrete base are used, the blocks will often settle in a slightly skewed position.

Plastic “Wood”
 Easy to work with, like lumber. No splinters.
 Made from recycled consumer plastic waste.
 Has a long life and won’t rot.
 Easy to add a wire-mesh bottom.
 Easier construction of odd-angled shapes such as octagons or pentagons.

 Up close, looks very fake.
 Expensive compared to lumber.
 Requires screws instead of nails for sturdy attachment.

Recycled, Untreated Rot-Resistant Lumber

The use of the two main rot-resistant lumbers available, redwood and cedar, is controversial due to environmental issues. They are, however, still the easiest material for building raised beds. (Use of recycled wood lessens environmental impact.)

 Good-looking natural surface.
 Available as recycled material.
 Easy to work with; no mask, gloves, or goggles required when using hand tools.
 Easy to add wire-mesh bottom.
 Can be used to construct odd-angled shapes.

 If in contact with the soil, may have to be replaced within 4-20 years. (Note: redwood heartwood can last this long, but white redwood sapwood usually rots within four years and should be avoided.)

So, the choice is yours. Happy gardening.

Please leave a comment- I'd like to hear from you.

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1 comment:

Howdyk said...

Thank you for the information. I've been gardening in a small space for the last couple of years without much success in Portland, Oregon. Maybe raised beds will be the answer