Master Gardener: What to Know Before Building a Raised Garden Bed | Home & Garden


Tom Ingram Ask a Master Gardener

Last Tuesday we talked about the pros and cons of in-ground gardens versus raised gardens. This week, let’s talk about how to build a raised garden as well as what is called a square foot garden.

One of the benefits of 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 spot in our yard that got the best sunlight. The downside was that this place was on a fairly steep incline that slanted in two directions. And as if that weren’t enough, we decided to build it in the shape of a trapezium. Maybe not our best decision, but luckily his math skills weren’t as rusty as mine and we now have a unique raised bed that is 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 not exceeding 4 feet in width as anything over 4 feet wide will be difficult to work with without having to walk around your garden. Walking in your garden can compact the soil and damage the roots, so it’s always a good idea to keep them at a width that allows you to reach everything outside of the raised bed.

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A common mistake is to make your raised bed too deep. Raised beds should only be about 6 to 8 inches deep, as most plant roots remain fairly shallow. Also, the more you build the sides of the bed, the more soil you will need.

You can use a variety of materials to construct your raised beds, but most tend to be constructed from wood or concrete blocks. If you’re not one to build, you can order pre-made kits quite inexpensively. You can also use a livestock waterer, but the more you have, the higher your start-up costs will be.

One thing we don’t recommend using for raised beds are railroad ties, as they can release creosote fumes 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 yourself from dust while sawing. My favorite is rough cedar, but it can get expensive.

Depending on where you plan to build your raised bed, you will likely need to weed out the grass that is there now, especially Bermuda. Once you’ve gotten rid of the grass, lay a garden drop cloth across 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 several ways to do this. Personally, I like to contact a flooring company and have the flooring delivered. Since they have a variety of floors to choose from, all you have to do is figure out how much your wallet can handle and order the best floor you can afford. Since everything you’re going to grow depends on the soil, it’s usually not a good place to skimp.

You can also buy bagged soil from your local garden center to fill your raised bed. But do a little math beforehand and you might find that it’s cheaper and possibly easier on your back to have the floor delivered by a specialist floor company. When ordering soil, you will need to determine how many cubic meters of soil your bed will need, but the soil supplier can usually help you determine this part.

Now let’s talk about a variation of the standard raised bed. The first time I heard of a square foot garden was when my brother was traveling 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 divided into 1 foot by 1 foot squares. These gardens are typically 4 feet by 4 feet, giving you 16 individual sections.

Typically, you plant a different crop in each square foot or perhaps sequentially plant the same crop in multiple squares. Succession planting means you can plant radish seeds every week in a different patch for 4 weeks. Since you planted successively, they will be ready to be harvested successively. This will help you have fresh vegetables for longer. You can plant in succession in any type of garden, not just square footage 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 every year and love it. It takes up less space and lifts the cucumbers off the ground, putting them further away from insects who think the cucumbers are delicious.

Don’t forget that our annual plant sale/fundraiser is underway, and we have a great selection of vegetables and flowers for you. See you soon in the garden.

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You can get all your gardening questions answered by calling the Tulsa Master Gardeners Helpline at 918-746-3701, visiting our Diagnostic Center at 4116 E. 15th St., or sending us a email to


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