University of Illinois Extension

Raised Beds

Expanding your garden? Whether growing flowers, vegetables or shrubs, consider planting in a raised bed, said Nancy Pollard, U of I Extension horticulturist. "It will offer improved productivity, often healthier plants, and easier maintenance than an in ground bed," said Pollard. "Raised beds allow the soil to warm up earlier in the spring. The soil stays loose as long as you do not walk on it. The soil drains better. There is better air movement, so there are fewer pests.

"Working with a raised bed will be easier on your back. Benefits are gained from raising the bed as little as six inches. Twelve to sixteen inches is ideal for deeper rooted plants. If you want the bed to be wheelchair-accessible build it about 27 inches deep."

Raised beds that are against a wall or fence should only be about two and a half feet across, so you can reach to the back of the bed easily. If both sides are accessible, then the bed can be four to five feet wide, so you can still reach to the center without stepping in the bed.

"You can create a simple low mound six to eight inches high, by excavating the paths in between and piling up the soil," she said. "Then till in four to six inches of well-rotted compost, peat moss, or other organic matter. If you excavate the paths, be sure to later mulch them to keep the weeds at bay. The bed ideally will have a flat top with sloping sides at about 45 degree angle. Never walk on the bed, as it will compact the soil, causing you to lose some of the benefits of raising the bed."

A simple way to create a raised bed with less digging work is to build a frame over an existing lawn area. Lay down six to eight layers of newspaper, wetting the paper with a watering can so it does not blow away before covering it with a soil and compost mix.

"The newspaper will create a barrier to keep the grass from growing into the bed," she said. "Be sure to overlap the seams. Never just cover the grass with soil. The grass must be killed in some way, or it will be an ongoing battle to get rid of it in your raised bed. It helps to leave a four-inch strip of mulch around the bed to make mowing easier and to keep the grass and weeds from encroaching."

The choice of soil mixture to fill the bed is very important. The mix should be one-third to one-half compost. Be sure the soil does not come from an area that was contaminated with lead, arsenic or pesticides. If possible find out the pH of the soil. A pH of 6.0 to 7.0 is good for many garden plants. The pH will affect whether the plants are able to take up the minerals they need from the soil.

"It does little good to create a raised bed if the pH is too high or too low for what you plan to grow," said Pollard. "Purchase one-third to one-half organic matter, or compost, and the other one half to two thirds soil. Mix them together and fill the bed. Let it settle for a week or so, and then let the planting begin."