Garden Docs: Build the perfect raised garden bed

Size, materials, good soil and compost assure success

John J. asks: Can you give me some guidelines for making raised beds? I will be using them to grow vegetables and annual flowers.

The first rule of thumb is to not make them too wide. One of the biggest benefits of having a raised bed or two is not having to deal with soil compaction. So when you construct your beds, you should be able to work in them without stepping in them.

For this reason, raised beds should be approximately 4 feet wide. Most people can comfortably reach into the center of a 4-foot-wide raised bed without any problem. Depending on your height, a 3-foot span might be even more comfortable.

Consider the placement of the bed. If the raised beds are going to be next to a fence, 3 feet wide might be what’s needed so you can easily work in your bed from one side. Unless you plan to water your raised beds by hand with a hose (that’ll get old quick), you'll need to decide on how you will water the beds. Build the raised beds near a water source. Soaker hoses or drip irrigation work well for raised beds. If you have a few raised beds and garden areas with perennials, shrubs and such, set up a drip irrigation system.

There are many materials you could use to construct your raised beds. Do not use pressure-treated wood manufactured prior to 2003 as it contains chromated copper arsenate, and you don’t want that in your vegetable garden. Many people use rot-resistant and chemical-free woods such as cedar or redwood.

For something a little less expensive, you could repurpose an old wood fence you took down or steel panels. Avoid old railway ties, which contain harmful creosote. Galvanized water troughs seem to be very popular and last a long time.

Choose a high-quality soil for the raised beds. Check with your local landscape suppliers who make soils specifically for raised beds and containers. Avoid soils that are mostly sand or nitrogenized sawdust.

If you are making more than one bed, leave enough room to work in between them, about 2 to 3 feet. Be sure you can get a garden cart or wheelbarrow between the beds. And don’t forget room for a stool or chair!

If you don’t want to be weeding the grasses and weeds that pop up along and around the raised beds, put down a barrier, such as flattened cardboard boxes or newspaper, and add a layer of mulch on top. It’s an effective way to keep down the weeds. Skip the landscape fabric because the weeds will eventually get through anyway.

One huge advantage of growing in raised beds is that the soil heats up more quickly in the spring compared to ground soil and that enables an earlier planting. But they also heat up more as the season goes on. Putting a layer of mulch on top of the soil will help regulate the temperature. Mulch also regulates moisture. During the rainy season, it acts like a sponge, absorbing the rainfall. During the hot summer months, mulch helps keep the soil moisture from evaporating so you don’t have to water so often. You will find that mulched raised beds will have much healthier plants than those without it. Any organic composted material will work well.

Dana Lozano and Gwen Kilchherr are garden consultants. Send your gardening questions to The Garden Doctors, at pdgardendoctor@gmail.com. The Garden Doctors can answer questions only through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.