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Index : Miscellaneous Gardening Topics
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- 22. Gardening in Raised Beds - Top
- Year-round sun and the image of vine-ripened tomatoes have lured many Tucson homeowners into starting a garden. But even the most enthusiastic gardener may get discouraged after attempts to work with our native desert soils. A number of obstacles such as caliche, gravel, heavy clay, and even sand await many would-be gardeners.
Smart gardeners have outwitted these difficult conditions by planting above ground in raised beds. Raised beds are like big bottomless containers. They consist of a frame, that may be built with concrete block, slump block, stone, wood or brick. The frame rests directly on the ground and creates a gardening bed that is usually twelve to eighteen inches above ground level.
Raised beds offer gardeners several advantages. They give you the chance to improve poor soils and avoid soil-borne disease problems. You choose and install the soil mix you want for your raised bed.
Tending raised beds is easier. Since they are elevated, it takes less bending over to work with your plants. The bed form can be used as a bench if it's built of a wide material, such as concrete block. Not having to walk among the plants keeps you cleaner, and your plants happier too. Their not exposed to the soil compaction problems that foot traffic brings to in-ground gardens.
A prepared soil mix in raised beds assures better drainage. This is especially important on poorly drained sites. Root diseases are less likely to develop when beds are raised. Soil in raised beds also remains airy and easy to work.
When making a raised bed, start small. The fun of gardening can quickly turn to drudgery in a garden that's too large. A frame that is twelve inches tall and eight to ten feet long is a good beginning size. Determine the exact length based on the materials you plan to use. Landscape or pressure treated timbers, for instance, are commonly sold in eight foot lengths. An eight foot bed eliminates the need for cutting. The width of the bed should be four or five feet wide, again, depending on the length of the materials you select. Wider than five feet makes it difficult to reach into the center of the bed.
Locate the bed in an area that receives morning sun, but some mid-day and afternoon shade. This is very important in the spring and summer months when afternoon sun can wilt most garden plants. Take advantage of trees to provide afternoon shade, but avoid placing beds directly under trees, even ones that cast light shade.
Because soils in raised beds are by nature, well drained, watering is important. An inexpensive drip tubing irrigation system is a must. A four foot wide bed will require two drip tubes running parallel down the length of the bed. Inexpensive, battery operated irrigation timers are the best device to use to insure regular watering.
Adequate nutrients and water are especially important for intensively planted, raised beds. Making the most of your raised bed plot requires growing plants close together. Extra fertilizer and water will help, but there is no substitute for deep, fertile soil high in organic matter.
Work the top six inches of soil, adding organic matter, in the area where the frame will sit. Once the frame for the bed is in place, fill in using home or bagged compost, potting soil or bagged topsoil. Amendments like sharp coarse sand or perlite can be added, and will increase the aeration and drainage if the soil is too heavy. It's important that the soil be well-drained.
Fertilizer should be mixed into the soil at the time the raised bed is filled or prior to planting. Use ammonium phosphate or a vegetable and flower fertilizer at the rate of 1 to 2 pounds per 100 square feet of bed.
When planting raised beds, avoid the tendency to line up plants in rows. Seeds and plants should be planted in wide bands of several rows or broadcast in a wide strip. The idea is to space plants so that their leaves will touch at maturity. This saves space. It also shades the soil, which reduces moisture loss and discourages weeds.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
- Updated: February 22, 2004
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