Where to build your raised bed
A raised bed should be located in full sun for maximum yields. That means at least 6 to 8 hours of direct sunlight daily. It should also have easy access to water and be protected from the prevailing winds. To make sure the plants receive as much sunlight as possible, orient your beds north-south.
Materials and dimensions
Although wooden boards are often used as sides to hold the soil in place, you can also choose flat rocks, concrete blocks, logs and decorative bricks or other materials. It all depends on what is available, your budget and your preferred style. It’s best to use locally sourced, long-lasting materials. If you’re using treated wood, make sure it does not contain any toxins.
In most cases, gardeners build a low frame, 15 to 45 cm high. If it’s difficult for you to bend over or kneel down, you can also build a hip-height elevated bed. In that case, you’ll need 30 to 45 cm deep boxes set on legs. Remember that such elevated boxes require drainage holes.
You’ll need to add soil to a depth of at least 15 to 30 cm for good drainage and proper root development. You can also have higher sides on your beds, but that will mean adding more soil.
The length of your beds will depend on your site and personal preferences. They are usually 120 to 360 cm long. The optimal size is 120 cm wide by 360 cm long.
Preparing the soil
Although you can use your existing soil and amend it with compost and organic fertilizer, in most cases you’ll need to add some planting soil, sold in bulk or bags. Avoid black earth and mixtures containing a lot of peat moss, which will not perform well over the long term. Soil in elevated beds dries out quickly, so it is important to use a water-retaining mix. Your soil should contain 25 to 30% compost. You may also wish to add a small amount of clay, to help it retain moisture.