My goal with this post is to help you think about some important concepts before you invest your time, money, and effort into buying (or building) and installing a raised bed. I won’t go into any great detail – I just want to give you a quick but comprehensive tour of the major considerations.
If you want a fairly tall and handsome raised bed (like the ones seen in the photos on this site) that is built to last, you are going to be tackling a major project with significant costs attached.
You will want to get things right the first time!
The Right Material
Most raised garden beds are made of rot-resistant woods like redwood or western red cedar. These materials look great and are fairly easy to work with, but because they are in contact with soil and water inside of your raised bed, they can only be expected to last 10 years or so (and they are fairly expensive).
Never use pressure-treated wood or railroad ties for building a raised bed that you plan to grow fruit or vegetables in (because of the toxins used to preserve these materials, which will leach into your soil).
Stone is a great option for building raised beds that will last much longer than wooden ones. Stone can also be very attractive. However, stone can be harder to work with and more expensive (unless you have native stone on your property that you can gather for free!).
One great advantage of a stone-walled raised bed is that it will help to extend your gardening season – your soil will warm faster in the spring and stay warm longer into the fall. Stone accomplishes this feat by absorbing and storing heat during the day and slowly releasing it into your soil during the night.
Cinder block is another great material for building a long-lasting raised bed, and like stone, it will store heat and help to extend your gardening season. It is easier to work with and less expensive than stone.
Of course, brick is a material that is often used to build raised beds, as well as landscape stones (which don’t involve mortar and require less skill to work with than brick).
The Right Location
The ideal location would probably have full sun, but if you don’t have that then just pick the sunniest spot you can.
A location with afternoon shade would be preferable to one with morning shade, as most plants love morning sun and in hot climates could probably benefit from some late-afternoon shade.
A location with dappled shade would probably be preferable to one that has a solid shade for part of the day, but again you do the best with what you have. I have a big garden area that is in and out of both dappled and solid shade during the day and it is a wonderful area that produces well for me.
Try not to place your raised bed in a low spot or with poor drainage.
Finally, place the raised garden bed as close to your house as possible to maximize the convenience of working and harvesting your special garden area. Don’t underestimate the importance of convenience!
The Right Width And Length
Your raised bed should be no wider than 4 feet, which will allow you to reach into the middle from either side.
If your raised bed will only be accessible from one side (for example, if it is placed directly next to your house or a fence), then it should only be a maximum of 2 feet wide.
Your raised bed can be as long as you like, but you will want to think about convenience here and not make it so long as to be a bother to walk around.
The Right Height
A raised bed should be a minimum of 6 inches tall. According to most experts, a depth of 6 to 12 inches of high-quality soil mixture will give you the best balance of benefit and cost.
Raised beds of the 6 to 12-inch tall variety can be very quick and simple to build, and not very expensive to fill!
That said, a taller raised bed can give you some important advantages over shorter ones:
- a taller raised bed will be less likely to be stepped into by yourself or others (kids, dogs, wild animals)
- if your raised garden bed is surrounded by bermudagrass, a taller raised bed will be less easily invaded from under the sides (or over the sides)
- a taller raised bed is much more convenient to work in, as the level of the soil is closer to your hands
- a raised bed of 16 to 20 inches in height can double as a bench/seating area (especially if you top the sides of your bed with a nice 6 to 10-inch wide plank)
- the taller the raised bed, the more protected your plants will be from the coldest air (which is heavier and settles in low spots) – so you create a warmer microclimate for your plants by lifting them up off of the ground level
- the taller the raised bed, the more difficult it is for your plants to be affected by blowing weed seed and some insects and pests
The Right Walking Lanes
If you are building or installing multiple raised beds, you will want to keep your aisles or walking lanes a minimum of 2 feet wide. This will give you plenty of space to maneuver without being tempted to step into your raised beds.
You might even want to make your aisles a little wider than 2 feet if you want to get a wheelbarrow or garden cart into the raised bed areas.
The Right Soil Mixture
You can’t go wrong with a 50/50 mixture of quality screened topsoil and compost. Mix, don’t layer, these two ingredients into your raised bed.
It is preferable to use a blend of composts from different sources, if possible (including your own homemade compost!). This will give your beds a nice variety of nutrients and other characteristics.
Other great amendments for your raised bed soil mixture include peat moss (or coir) and vermiculite (or perlite).
The compost in your soil mixture should provide all of the nutrients your plants will need (so no need for fertilizer!), but you will need to add some more compost every season as the old compost is used up by your plants.
If you do add fertilizer, go with a balanced (1-1-1 or 2-2-2), organic, slow-release variety.