A raised bed of vegetables and flowers in a urban garden

Raised beds provide the means for a beautiful, colorful edible garden.

Q: It is getting harder for me to do all my gardening bent double. My husband will build me raised beds, but we have no idea what size they should be. Are there any standards?

A: There are. You have a few choices for all three dimensions. First, the height: if you want to continue working from standing and kneeling positions, plan your beds to be eight inches high. A little higher is possible but not necessary. To assure good drainage and enough space for roots, do not put a barrier like landscape cloth or plastic at the bottom. Just fill the beds on top of the existing soil.

The one case that is different is if you are creating beds to keep tree roots out of the garden. Begin those beds with a foundation layer of landscape cloth. It will prevent tree roots from invading the beds from the bottom up.

If you want to sit on the edge of the bed, you can make the raised beds 16 or 17 inches tall. That is the height of a chair seat. You might want to top the bed sides with a horizontal board for a comfortable perch. If you want to use a separate seat while gardening, you can make the beds 28 to 30 inches tall. That is the height of a table. Beds that height even works for wheelchair gardening.

The higher the bed, the greater the force with which the dirt inside tries to push the sides apart. The walls of beds need strong corners. Tall beds need ties every few feet to hold the long walls together.

As for bed width, one important thing is to make it comfortable to reach the center while gardening. A bed four feet square will permit that. For longer beds, limit the width to 36 to 40 inches. That makes the reach comfortable from the long sides. Beds can be as long as will fit into the landscape.

The path around a bed is easily forgotten but should not be. Make it at least 18 inches wide. I did not know that when I built my raised beds, and I have been regretting it ever since.

Fill the finished beds with a mixture of one quarter container soil, to be sure of good drainage, and three-quarters topsoil. Taller beds need soil only a foot deep; the bottom of the bed can be filed with any kind of available rubble, from rocks to aluminum cans. A layer of something like landscape cloth on top of the rubble will allow water to drain while keeping the good soil up to where the roots are. My vegetable garden is on a south slope. When we built the beds, we terraced the slope, using the excavated soil as part of the fill in the beds.

Instead of wood, the sides of raised beds can be metal, rocks, even bricks. Theoretically, the beds can be just dirt piled up, but I do not recommend that in this climate. So much water evaporates from the uncovered sides that beds must be irrigated twice as often as flat ground.

Finally, wood for raised beds can be either treated or untreated lumber. Although the currently used wood preservatives are not poisonous, untreated lumber will not begin to rot for several years.

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You will find that gardening is easier in raised beds. There is less weeding to do because plants are spaced the same distance apart in both directions; there are no spaces between rows to become weed gardens. When small plants like carrots are in rows, use short rows running across the bed. The paths around the bed become weedy, but constant foot traffic smashes many of the weeds. Or paths can be covered with wood chips or carpet scraps. After a disastrous attempt to cover mine with black plastic, I let them gradually turn into mown grass.

Because the soil in a raised bed is never compacted by being walked on, it remains fluffy and never needs tilling or spading. That eliminates another big job.

Q: We may not plant a garden next summer. What would you suggest as a cover crop? We will continue to irrigate the area.

A: A good cover crop will, as its name suggests, cover the soil to protect it from blowing away or being taken over by weeds. Additionally, the cover crop remains will feed the soil for the following year. That means that the cover crop should blanket the soil surface before weeds grow very much. The crop also should provide a source of nitrogen. Finally, it should break down quickly, so that gardening the following year does not begin with tilling and chopping its remains.

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Those requirements mean making your choice among annuals. Perennial crops can be mowed before they flower and make seeds, but it will require hard work to chop up the root mass, and the roots will be slow to decay. Often legumes are used as cover crops because they manufacture nitrogen in a form usable by other plants.

If you talk to various organic farmers, you are sure to find that they have different cover crop favorites. I might try field peas, or even garden peas, since they grow early, provide a dense cover, and will break down reasonably well. You would want to pull or cut the vines before the seeds turned brown. If you leave the dead plants to blanket the ground for the rest of the growing season, the garden will need only minimum raking before it is planted the next spring.

Any annual plant could serve your purpose, though, as long as you do not permit it to make seeds. You might even consider the idea of seeing what plants volunteer in the area and mowing them all summer whenever they reach a height of four inches or make flowers, whichever comes first. That would be a labor-saving alternative to deliberately planting a cover crop.

If your garden spot is part of the view from your living room window, think about a cover crop of annual flowers--perhaps petunias or pansies if you are going to buy plants, cosmos, cornflower, or love in a mist if you want to start from seeds.

Q: My vegetable garden has grown poorly this year, and I don't know why. I did get a late start and didn't get it watered as well as usual for the first two weeks. Would either of those things have made problems?

A: Yes, they would. Although a few vegetables--like lettuce--don't care when they are planted, for many vegetables the planting window is open only a short time. If planted too late, they will be dwarfed and may not mature at all. Dry soil in their early days would add to their slow development.