So what's the big deal about raised garden beds? You get more bang for your buck with RGBs, in that you can produce more vegetables in a smaller area since you are not having to walk in between the rows of plants. Planting veggies so close together that the leaves touch can create a microclimate under the plants, keeping the plants warm and blocking out sunlight which discourages weed growth. RGBs will ensure that no one tramples across your garden soil, and keeps the dirt from getting compacted, making it easier for your plants to root. Above ground garden beds also stay warmer than the earth. Rodents and insects may have a harder time penetrating your crop -- some people tack up copper strips around the outside of the bed to keep out slugs. Plus, they are easier to work in since you are not bending over the ground -- the planting surface is at a higher, more ergonomic level. And last but certainly not least, you can fill up the beds with the perfect mixture of sand, loam, compost, and soil to give your vegetables the best possible start to growing their way into your kitchen.
The first step is planning out the layout of your beds. Where in your yard do you have the most south facing sun? Keep an eye on the area of your yard that you are thinking about building beds, and watch how the sun falls on it during the day. Does the whole yard get sun, or only one part? Is there plenty of exposure to the south, or is the neighbors tall fir tree or house blocking you out?
Once you determine where you want to put your beds, decide on what kinds you want to build. The width and depth can vary depending on what you intend to grow. For instance, the Colorado State University Extension Program recommends that tomatoes be grown in a bed only 2 feet wide. They recommend that ten tomato plants would be best in a 2 x 20 ft bed.
Most raised beds follow the 8 ft x 4 ft model at a one foot depth. You don't want your garden beds any wider than four of five feet. If they are wider than this, you may have trouble being able to reach the center of your bed from the outside, causing you to have to climb up in the bed to work in the middle of the bed, and in the process defeating the purpose of uncompacted soil.
The depth of bed determines on how deeply the vegetables you plant will root. Here are a few examples from the Clemson University Extension Program:
Also plan how much space you want to leave between beds and around beds. Experts recommend at least three feet in between beds so that you can comfortably get down on your knees or kneel between them when working with the plants. You may want to leave more room if you wish to be able to maneuver a wheelbarrow through them.
Once you decide how many beds you want, how big they will be, and how far apart, you can plan your layout.
Don't make the mistake I did -- I built the beds first, and then had to drag the heavy things into place. If I had to do it over again, I would have staked it out first, or at least where I wanted the corners of my beds to be. Mark where the corner posts will go, and dig out a one foot hole with a post hole digger. Build your beds in place, and simply drop the corner posts into their respective holes as you go.
When deciding what materials to use for the bed, you must decide a) how much you want to spend b) how long you want it to last c) how pure you want the wood
Hardwoods such as cedar will last a long time, but may cost a pretty penny if buying new. Other woods may degrade faster over time. Reclaimed lumber can be utilized too, but ensure that it is free of hazardous materials or chemicals. Likewise, try to avoid buying pressure treated lumber if at all possible, as many of them contain arsenic and other goodies that you won't want to leach into your soil and vegetables.
I used to use lag bolts to hold the beds together, but this requires more tools -- sockets, wrenches, drilling pilot holes .... save yourself time (and money) by using outdoor deck screws. I used 3 1/2 inch deck screws from Home Depot and they worked out great. The beds were nice and sturdy, and the tan screws blended in well. I think it gives the beds a better aesthetic, and we always shoot for a balance of function and beauty.
You can build a raised garden bed in any number of ways. Some people use bricks, some people use wood -- my mom recently used a kiddie pool with holes drilled in the bottom for drainage, which seems to work well, too.
Regarding the wood construction, here is a diagram that I prepared for a class I recently gave to my Sustainable Food Systems and Education Farms class. It will produce an 8 x 4 ft raised bed that is one foot deep.
For the above model, you just need to buy six 8 foot 2x6s, one 8 foot 4x4, and box of deck screws. Too easy! If you wanted it an extra six inches deeper, just adjust the length of your 4x4 to 2.5 feet, and add another 2x6. Get creative and build more as you need, play with the dimensions and create exciting patterns in your yard!
Once you have the bed constructed, you may want to take it a step further. Before adding dirt, add a weed barrier which will significantly reduce weed growth once your beds get going. Place PVC pipes every four to six feet and arch them over the beds. Attach plastic sheets and transform your bed into a greenhouse. Or install drip irrigation systems or sprinklers to make watering easier on yourself. My good friend Ben recently came up and ran a drip system for me. It was cheap and easy and a Raindrip starter kit only runs about $30 from Lowe's.
Here are some more resources that you can use for your project. Have fun!
Building the Ultimate Raised Garden Bed
Sunset Magazine's Garden Section
Mother Earth News