Richard C. Bogren, Gill, Daniel J.
For Release On Or After 03/20/15
By Dan Gill
LSU AgCenter Horticulturist
March is a month when many gardeners begin to plant their spring vegetables. Raised beds can be the solution to a number of challenges when it comes to home vegetable gardens.
Raised beds drain faster during periods of heavy rain. Overall, raised beds are easier to maintain than traditional in-ground beds. And with careful management, they can be even more productive than typical garden beds.
As a result, the use of raised beds is becoming increasingly popular in home vegetable gardening. It’s also a great way to garden with kids.
Raised beds are generally about 8 to 12 inches high but may be higher. Raised beds built up high enough so you can sit on the edge while you garden are particularly easy on the back. They can allow gardeners with physical limitations or those that can no longer bend over easily to continue gardening.
The width of a raised bed should generally be no wider than you can comfortably reach into the middle when standing just outside the bed or sitting on the edge. For most adults, a bed 3 to 4 feet wide is best. The length of the bed is up to you.
You should be able to plant, weed and harvest while staying outside the bed and reaching in. This allows you to avoid walking in the bed once it is planted. Walking in the bed after planting reduces the planting area and compacts the soil.
You may construct the sides of the raised bed with a variety of materials, such as landscape timbers, bricks, cinder blocks, plastic lumber, rot-resistant wood like cedar and redwood or pressure-treated lumber (2-by-12-inch boards work well).
In our climate, rot and termites are real concerns. Even rot-resistant wood can succumb to these problems. Using materials such as pressure-treated wood, plastic lumber and cinder blocks will create a more permanent raised bed. The bottom of the raised bed is left open – the sides simply sit on the existing the ground. This ensures good drainage.
For construction tips, you can find much information on the Internet. Building small beds is something a person with average skills should be able to do. Building larger or taller beds needs more careful planning, so you may want to hire a carpenter.
Once constructed, raised beds will need to be filled with soil. Before adding the new soil, kill or remove any unwanted grass or weeds present in the bottom. The herbicide glyphosate – the active ingredient in Killzall, Eraser, Roundup and other brands – may be used to do this.
Till the soil in the bottom of the raised bed, add a few inches of organic matter and work that in before filling the bed with soil. The roots of the vegetables may grow down into the existing soil at the bottom of the bed, particularly if the raised bed is less than 12 inches deep. This creates a transition that helps the roots grow deeper. If tilling is impractical, you can simply put the soil mix in over the existing soil after the weeds are dead.
If sandy soils are available, such as creek sand or river sand, you may use those to fill the raised beds. Add about 7 inches of sandy soil to the raised bed. Next, sprinkle a general-purpose or organic fertilizer over the bed following label directions. Then, spread about 3 inches of organic matter, such as compost, rotted leaves or aged manure. Finally, thoroughly incorporate the organic matter and fertilizer into the soil, and you are ready to plant.
The soil level should be a couple of inches below the edge of the sides. This facilitates watering. And remember, you need space for the mulch you will use to cover the soil.
Instead of blending your own soil mix – sandy soil plus organic matter – you might choose to purchase a blended soil mix often called topsoil or garden soil from a local company or nursery. The soil company or nursery can help you decide how much soil you need based on the dimensions of the raised beds. Make sure the organic matter in the mix, such as ground pine bark, has been well composted. If it’s not, you may need to add a nitrogen-containing fertilizer occasionally while the organic matter breaks down.
For small-scale gardens, it’s often easiest to purchase bagged soil mix from a local nursery. For larger jobs, some nurseries and soil companies sell blended soil mixes by the cubic yard and deliver it if your order is large enough. You can often get it yourself if you have a pickup truck.
It’s a good idea to incorporate a general-purpose commercial fertilizer or organic fertilizer to the soil mix before planting. This will ensure sufficient nitrogen in the soil for the plants. It also will help compensate for any nitrogen that may be tied up if the organic matter if the mix is still decomposing, which is less of a problem if the organic matter was well composted.
New soils often get better with age, and gardeners will talk about purchased soil mixes “mellowing” over the first six to eight months after they are put in place.
If you have been thinking of starting a vegetable garden but were put off by the hard work of bed preparation, building raised beds is an option. A fair amount of work is involved in putting them in place to begin with, but there tends to be less labor over time. This is an advantage for both older gardeners and young children who would find the physical demands of preparing in-ground beds challenging.