Master Gardener: What to know before you build a raised garden bed | Home & Garden

Tom Ingram Ask a Master Gardener

Last Tuesday, we talked about the advantages and disadvantages of in-ground versus raised bed gardens. This week, let’s talk about how to construct a raised bed garden as well as something called a square foot garden.

One of the great things about raised beds is that you can build them in just about any shape you want. A few years ago, our youngest daughter and I set out to build a raised bed in a location in our yard that got the best sun. The downside was this spot was on a pretty significant incline that sloped in two directions. And if that wasn’t enough of a challenge, we decided that we wanted to build it in the shape of a trapezoid. Maybe not our best decision, but fortunately her math skills were not as rusty as mine and we now have a unique raised bed that gets put to good use every year.

When building a raised bed, size is the first thing that usually needs to be determined. The key thing to remember is that you can always build another one, so don’t get carried away. We suggest you do not go over 4 feet in width because anything over 4 feet wide will be difficult to work without having to walk around in your garden. Walking in your garden can compact the soil and damage roots, so it’s always a good idea to keep them to a width that allows you to reach everything from outside the raised bed.

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One common mistake is making your raised bed too deep. Raised beds only need to be about 6 to 8 inches deep since most vegetable roots remain pretty shallow. Plus, the taller you build the sides of the bed, the more soil you are going to need.

You can use a variety of materials to build your raised beds, but most tend to be constructed out of wood or concrete blocks. If you are not the constructing type, you can order pre-made kits pretty economically. You can also use a livestock watering trough, but the fancier you get, the greater your start-up costs will be.

One thing we don’t recommend using for raised beds are railroad ties because they can release creosote vapors that can burn your plants. Treated wood is fine because it doesn’t contain the toxic chemicals it once did. But, if you choose to use treated wood, be sure to wear a dust mask and protective clothing to protect you from the dust while sawing. My personal favorite is rough cut cedar, but that can get pricey.

Depending on where you plan to build your raised bed, you will probably need to eliminate the grass that is now there, especially Bermuda. Once you get rid of the grass, lay down some garden cloth at the bottom of the bed to help discourage future grass growth in the area.

Now that your bed is built, you will need to fill it with soil. There are a couple of ways to go about this. Personally, I like to contact a soil company and have the soil delivered. Since they have a variety of soils to choose from, all you need to do is determine how much your wallet can bear and order the best soil you can afford. Since everything you are going to grow depends on the soil, this is not usually a good area to skimp.

You can also purchase soil by the bag from your local garden center to fill your raised bed. But do a little math ahead of time and you might find out that it’s cheaper and maybe easier on your back to have the soil delivered from a soil company. When ordering soil, you will need to figure out how many cubic yards of soil your bed will require, but the provider of the soil can usually help you figure that part out.

Now, let’s talk about a variation on the standard raised bed. The first time I heard of a square foot garden was when my brother was heading to the Philippines to work with the Peace Corp teaching people how to garden using this technique. Basically, a square foot garden is a garden sectioned off into 1-foot by 1-foot squares. These gardens are typically 4 feet by 4 feet, which gives you 16 individual sections.

Typically, you would plant a different crop in each square foot or perhaps succession-plant the same crop in multiple squares. Succession planting means that you might plant radish seeds every week in a different square for 4 weeks. Since you planted in succession, they will be ready for harvest in succession. This will help you have fresh vegetables for a longer period of time. You can plan succession in any type of garden, not just square foot gardens.

If you want to grow something like cucumbers in your square foot garden, you can grow them on a trellis to keep them from taking over the whole garden. I trellis my cucumbers each year and love it. It takes up less space and keeps the cucumbers off the soil, which places them at a greater distance from those insects that think cucumbers are delicious.

Don’t forget our annual plant sale/fundraiser is going on now, and we have a great selection of vegetables as well as flowers for you. See you in the garden.

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You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St. or by emailing us at [email protected]


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