Happy vegetables provide the best harvests, and no vegetable is happier than when it has its roots sunk deep into the organically rich, crumbly soil of a raised vegetable patch. Raising a vegetable bed growing area just 10 to 20 cm (4 to 8 inches) above the surrounding soil increases drainage and helps provide the airy, friable conditions vegetables love. A raised veggie bed also provides a clearly demarcated area where the soil won't be trodden on and compacted, according to Garden Organic. Although you can create a wall-less raised bed by simply piling up the soil, it's best to build walls to prevent the soil from levelling out over time.
You have more control over soil structure -- plants are guaranteed the depth of the bed of friable top soil.
Preparing the Site
Vegetables are sun-lovers, so choose a sunny spot for your raised vegetable patch, well away from shrubs or trees that will compete with your veggies for water and nutrients. Most level, open areas of ground will do but it's best to clear away the worst of the weeds and level any bumps or hollows before you build the raised bed walls.
It's a temptation to build a raised bed directly on top of an area covered with grass or weeds, but while the soil and compost mix in a raised vegetable patch smothers most grass and weeds, a few of the most vigorous might survive and grow through. Also, breaking up the ground beneath a raised bed helps worms and other soil creatures to move into the bed, and water to drain out of it. So dig over the area with a garden fork, and remove the grass, weeds and their roots. Then rake the soil until it's level.
Building the Walls
Treated timber planks screwed to wooden posts provide a long-lasting, stable wall for a raised vegetable patch. To create a timber wall you need planks, a timber post, a long tape measure, a saw, a rubber mallet, a spirit level, drill, exterior screws and a screwdriver. The amount of timber you need depends on the size of the vegetable bed. You should be able to reach into the middle from the sides, which means the bed should not be much wider than 1.2 metres (4 feet).
To build walls for a raised vegetable patch 1.2 m (4 feet) wide, 2.4 m (8 feet) long and 20 cm (8 inches) tall, you need six 19mm x 100 x 2400 mm treated timber planks, one 47mm x 47 mm x 2400 mm treated timber post and 24 No. 8 50 mm external grade screws.
1) With a tape measure and a pencil, measure and mark the centre of two 19mm x 100 x 2400 mm planks, and cut them in half with a saw.
2) Measure and mark and cut the timber post every 400 mm, which gives six sections.
3) On the prepared site, measure and mark a rectangle 1.2 m wide and 2.4 m long with bamboo canes and string. The timber posts will sit just inside the edges of the vegetable patch, and the planks will be screwed to them to form the walls.
4) Hammer a post section into the ground with the rubber mallet at one corner of the rectangle. Stop regularly and use a spirit level on the top and sides to make sure it stays level and perpendicular to the ground. Allow at least 200 mm of the post to remain above ground.
5) Drive three posts into the ground in the same way at the other three corners of marked rectangle. Double check the distances between the posts are correct by holding the planks between them. The planks should cover the post edges facing out of the vegetable patch.
6) Drive the two remaining posts into the ground halfway between the posts on the longer sides of the rectangle.
7) Place a 1200 mm plank against the posts along a short edge of the rectangle, and drill two pilot holes through the plank into the posts with a 2.5 mm bit, 25 mm from the top and bottom of the plank. Screw the plank to the posts using external grade, 50 mm No.8 screws and a screwdriver.
8) Attach timber planks to the other posts in the same way, to form the lower half of the raised bed wall.
9) Attach the remaining timber planks to the posts above the lower planks, to complete the walls of the raised vegetable bed.
Filling the Bed
A mixture of 50 per cent compost and 50 per cent topsoil provides good soil structure and plenty of well-drained organic matter in a raised vegetable bed. It's important not to use only compost in the bed because compost dries out quickly in hot weather, according to Garden Organic.
Use soil from elsewhere in the garden or commercial topsoil, and homemade garden compost, green waste compost or commercial compost, or a combination, to fill your raised vegetable bed. To fill a 1.2 m x 2.4 m bed, you need 0.3 cubic metres of soil and 0.3 cubic metres of compost.
1) Fill the bed with the soil and compost, and mix them together thoroughly with a garden fork.
2) Wait a week or two before sowing seeds or planting vegetables, to allow the soil and compost mixture to settle.
3) Over time, the raised bed contents will settle further. Keep the bed topped up by spreading a mulch over the soil surface, which conserves soil moisture and helps control weeds.
A Brick-Walled Bed
Garden Organic says that bricks walls around a raised vegetable bed help insulate the soil from temperature fluctuations. Bricks heat up more slowly than wood, and lose heat more slowly, too. On hot days a brick-walled bed helps protects vegetables from heat, and keeps them cosy and snug at night by releasing heat generated from sunlight during the day.
Brick walls need a solid, level concrete base, which is called footings, to prevent them from cracking. To build a brick-walled bed, as well as bricks, you need concrete, a spade for mixing it, mortar, a mortar trowel, a spirit level and string and posts to help lay the bricks in level layers. Trenches must be dug beneath the walls to lay the footings before laying the bricks.