I love love love growing vegetables in raised beds. No tilling, hardly any weeding, no run off, no muddy shoes and a border to sit on. In North Tacoma, we have lead and arsenic in our soil from the old smelter. By growing in a raised bed we can control the type of soil we put in it. Now it does take some effort to build one, but once it's made, it makes gardening so much easier.
There are many ways to build a raised bed and many resources and designs available. Here are my tips.
Start by identifying the sunniest areas of your yard. Vegetables need at least 6 hours of direct sunlight, but will do better with more. Once you select your site, measure your space.
A well designed bed is one that you won't have to step into to garden. You want to be able to reach in from the sides. This will allow you to use the space more efficiently because you won't need walking rows between your crops. You also won't be compacting your soil with your footsteps. Four feet wide is the max I'd go. For shorter people, like me, I recommend three feet wide. I have both three and four foot wide beds and much prefer the three foot wide ones. My husband prefers the four foot wide beds. Length can be determined by your space or you can go with standard board lengths to minimized cuts. If you go with 12 foot boards, I'd brace them in the middle, so that they don't warp and pull apart. For depth, you can go as low as 8 inches if you have good soil underneath them. If you're putting your bed over concrete or bad soil, I'd go with at least 12 inch deep. You make them as tall as you'd like. If you have trouble bending down you can go 20 inches deep or more. Just remember that the taller you go, the more soil you need and also if you go too high it might make harvesting more difficult if you grow tall plants.
Its important to space your beds adequately to allow for easy access. Three feet between beds gives you space to maneuver a wheelbarrow and your hose. Three feet also allows room for people to get by each other. Remember that when plants get big, they will spill over the sides of the bed making your paths feel more narrow.
Typical materials include wood, concrete blocks, and rock. Wood is easy to work with and quick to put together. I'd go with untreated lumber. Cedar will last the longest, but is very expensive. Fir is fairly economical and will last five to ten years. Concrete and rock last forever, but is heavy to work with. You can also use salvaged materials and mix and match.
We put our wooden beds together with screws, but have found that bolts with washers stay in better. We didn't use the method where you put posts or brackets in each corner to hold them together. I'd recommend doing so, so you could just use screws or nails.
In the Tacoma area, we've tried several different soil products. We've bought Tagro Potting soil, 3-way topsoil with mushroom compost, and 5-way mix topsoil. We've eventually ended up mixing them up together to get a good blend. The Tagro Potting soil load we got had too much chunky organic matter like wood bark and didn't provide enough structure, although it grew some fabulous squash and corn. The 3-way with mushroom was overly silty, and the 5-way mix had some gravel and also was a little dense. Mixing different types of soil together made for a nice combo of structure and organics. We also supplement our beds with regular Tagro, worm casting, and compost when more organics are needed.
Whether you start with just one small bed or lots of beds, you'll find raised vegetable bed gardening so much easier than planting directly in the ground.