There are several materials you can use to build a raised bed garden. Some of the most popular are cedar, pine, and concrete blocks. The advantages of raised beds are numerous. The soil warms up earlier in spring, drainage is excellent, you do not have to till, and it’s easy to add a layer of compost twice a year to keep the soil healthy.
Most raised bed frames are a minimum of 6 inches high and 2 inches thick. The side boards are two inches thick for strength and durability. Remember you are using these boards to hold back a significant amount of dirt.
You can use 2X4 lumber if you are growing shallow rooted vegetables like lettuces or radishes, but most other vegetables need more depth. Tomatoes in particular need to be planted deep.
How wide you make the beds depends on whether or not you can reach the middle. If you want to build a bed four-feet wide, you would need to have access on either side of the bed in order to reach plants in the middle that need tending, and for weeding. Any width can work as long as you do not have to step in the beds to reach the middle. You do not want to compact the soil.
Building the Bed
You can use lumber the height you want your bed, or you can use narrower lumber and stack it to build whatever height you want. For example, you want to build the sides of your bed 24 inches high. You would simply build each box the width and length you want and stack them. To keep them together you would build braces on either the inside or outside.
You would need three 2X8X8 rectangles, two 2X12 rectangles, or two 2X10X8 rectangles and one 2X4X8 rectangle to build the sides to 24 inches.
Pressure Treated or Not?
It is not recommended that you use pressure treated wood in building beds for vegetables. The chemicals used in the pressurization process can leach into the soil and into your food. If you want to use this for longevity, cover the interior of the bed with sheet plastic and staple in place.