Raised garden beds, also called garden boxes, are great for growing small plots of veggies and flowers. They keep pathway weeds from your garden soil, prevent soil compaction, provide good drainage and serve as a barrier to pests.
The Benefits of Raised Bed Gardening
Raised garden beds (also called garden boxes) are great for growing small plots of veggies and flowers. They keep pathway weeds from your garden soil, prevent soil compaction, provide good drainage, and serve as a barrier to pests such as slugs and snails. The sides of the beds keep your valuable garden soil from eroding or washing away during heavy rains. In many regions, gardeners are able to plant earlier in the season because the soil is warmer and better drained when it is above ground level. Raised beds are also ideal for square foot gardening.
Raised garden beds are available in a variety of different materials, or they can be made with relative ease.
By raising the soil level, raised garden beds also reduce back strain when bending over to tend the bed. This is especially helpful for older gardeners or people with bad backs. And if the beds are built well, the gardener can sit on the edge of the bed while weeding. For some gardeners this is the biggest benefit of all.
Raised beds are not the same as garden planters. Planters are elevated containers which have bottoms to prevent the soil from falling out. Planter bottoms usually are slatted, with some type of semi-permeable cloth barrier which permits drainage. Raised beds, however, do not have bottoms; they are open to the ground, which offers the benefit of permitting plant roots to go further into the ground for available nutrients.
How to Build a Raised Garden Bed
Building elevated beds for your vegetable garden is simpler than it looks. You’ll need to decide what kind of wood to use, how tall you want the bed to be, and whether you want to build the entire bed yourself or use pre-made corner braces. These simplify the construction process and provide a secure corner that won’t loosen over time. You can also use concrete blocks or other materials for your beds, but wood is cost effective and readily available.
What Kind of Wood to Use?
In most cases, cedar is the best wood to use for garden beds because cedar is naturally rot resistant. Western red cedar is commonly used, but white cedar, yellow cedar and juniper are also high-quality choices for outdoor construction projects. Redwood is another excellent rot-resistant wood, but redwood is a more limited resource. How long the wood will last depends on the type of cedar and your local weather conditions. In our garden, we use red cedar for building the beds, and some of these beds have lasted 15 years.
How Tall Should the Bed Be?
You can build the bed to any desired height up to 36″. The most common height is 11″, which is the height of two stacked 2″ x 6″ boards. If you have good soil beneath the bed, the roots will go down deeper as needed to access more soil and nutrients, so you can even have beds that are only 6″ high. If you want a taller bed, remember that as you go taller, the weight of the added soil will add pressure to the sides, and will bow them outward. This is easily prevented by including cross-supports. We recommend using cross-supports in any beds which are taller than 18″, or longer than 6′. It is also important to consider the soil depth requirements for the roots of the vegetables you want to plant. Depending on the soil conditions beneath your bed, you may want to build the sides of your bed higher for certail crops. For more information, read our article Soil Depth Requirements for Popular Vegetables.
How Wide and Long Should the Bed Be?
We recommend bed width to be no wider that 4′ across. This is because it is easy to reach the center of the bed from either side, and for people with long arms, to reach across the bed. It’s important to keep the width this narrow to avoid having to step on the bed since this would compress the soil. The bed can be any length as long as cross supports are installed every 4′ – 6′ along the length of the bed to prevent bowing. We think longer beds are best, if you have the garden space.
We have built many beds over the years, and our construction process has evolved. The method described here is, in our opinion, the simplest method of building a raised garden bed, and it requires no special tools or expertise. Using this method, you can build your bed to any desired length, width and height.
Tools & Materials
Lumber
Use cedar “2 x” boards for the sides. These are commonly 2″ x 6″, but you can use 2″ x 4″ or 2″ x 8″ boards if this is what you have available. (2″ boards bought at a lumber yard are actually 1.5″ thick..) For the corner posts, use 4″ x 4″s, cut to 10″ longer than the desired height of the bed. If your bed is going to be longer than 8′, you’ll need extra posts to put in mid-span to prevent bowing and to provide a place to secure the cross-supports.
In the photos below, we used 2″ x 4″ boards for the posts instead of 4″ x 4″s. This is because the wood we had was full dimension, i.e., the 2″ thickness was a full 2″. If you get your wood from a mill, they can cut it full dimension for you.
Fastenings
Use 3.5″ #10 coated deck screws for the project. You’ll need six screws for each corner and two for each mid-span post. If you are using cross-supports, get a few 1″ stainless screws.
Cross Supports
Buy several lengths of 1/2″ aluminum flat stock. This is available at most hardware stores, usually in 8′ lengths. It is very easy to cut with a hacksaw and to drill for the screws.
Tools
Hand saw, square, carpenter’s level, mallet (or sledge), screwdriver, hacksaw, drill.
Is treated lumber safe?
In 2003, the EPA banned the sale of lumber treated with chromated copper arsenate (CCA) for residential use. Two compounds, alkaline copper quat (ACQ) and copper azole (CA-B), have now replaced CCA wood in the residential market. Both contain copper and a fungicide but no arsenic. The copper keeps insects at bay, and the fungicide prevents soil fungus from attacking the wood. In ACQ, the fungicide is quat, which is also used in swimming-pool chemicals and as a disinfectant. The other compound, CA-B, uses copper and tebuconazole, a fungicide used on food crops. According to Miles McEvoy, who works in organic certification with the Washington State Department of Agriculture, no pressure-treated wood is allowed in soils used to grow organic food. If you want to meet this high standard, choose a different material.
Until the safety of treated wood is proven conclusively, we recommend you use a naturally rot-resistant wood like red cedar, black locust or redwood. Under most circumstances, these woods will last 10 – 20 years. Recycled composite plastic lumber is another alternative, and is now available in a variety of sizes and colors.
Construction
Lay out the beds so they are horizontally facing south
It’s best if the long side of the bed faces south. This assures equal light exposure to all the plants growing in the bed. If your bed is aligned the other way (the ends facing south), you may have planting limitations because taller plants in front can block the sunlight to small plants in back.
Double-dig the bed area
If the ground has never been used for gardening, it should be ‘turned over’ (dug) to a depth of 16”. This gives you a chance to pull rocks, and to see the composition of your soil. Leave soil piled up in the center, away from the sides, so you can set the bed in place without obstructions.
Level the bed
Use a level for this task. This may seem overly meticulous, but after several waterings the soil will settle to level, and you’ll want the bed to be the same. Set a stiff board (2×4) on top of the bed sides, across the span, and set your level on this board. Tap down the sides as needed till you get a level reading. Be sure to check for level both along the length and across the width of your bed.
Check for roots
As you dig the soil, keep an eye out for any roots which may be growing beneath your beds. If left to grow, these roots will steal the organic amendments you add to the soil. Pull any roots back towards their source, and pull the main root clump. If the source is a living tree, you may need to install a root barrier by digging a narrow trench outside the perimeter of the bed, and deeper than the roots, and then insert a barrier such as heavy plastic sheeting.
Avoid stepping on the bed
Once the soil is added and the bed is planted, make it a policy to never step on the bed. Stepping on the bed will compact the soil, reduce aeration and impact root growth. Pets should also be trained to stay off the raised beds.
It’s very helpful to have a ‘spanner board’, a short sturdy board, like a 2 x 6, that’s just longer than the width of your beds. This board can be laid across the bed, setting on top of the bed sides, and can be used to set buckets on when weeding or adding amendments, and it can be used to step on if you must step on the bed. It also makes a handy seat when weeding or tending the bed.
Burrowing pests?
If your garden has burrowing pests such as moles, a layer of 1/2″ or 1/4″ hardware cloth (galvanized mesh) can be laid across the bottom, before soil is added. The mesh should continue at least 3″ up along the insides of the bed and be stapled in place. If you plan to grow root crops, such as potatoes or carrots, you may want to set the mesh lower in the ground by digging deeper when you are setting up the bed. There are also planters available for above-ground gardening. These planters are designed to be easy on the back.
Spread soil out evenly
Add any planned soil amendments, such as peat, compost or lime, and spread the soil evenly across the bed. Water the bed with an even, fine spray. This will settle the soil; add more soil to “top off”. (Over time the soil will settle an inch or two more.) Rake the bed once more to even out the soil and you’re ready to plant. To learn more about developing the ideal soil, read our articles:
6 Tips for Building Soil in your Raised Beds and Planters
3 Useful Soil Mixes for Planters and Raised Bed
Leave a generous width between beds for the pathways
It helps when pathways between beds are wide enough for a small wheelbarrow. For grass pathways, make sure they are at least wide enough for a weedeater or a small mower. (In our raised bed gardens the pathways are 22″ wide.)
Mulch the pathways between beds
Weeding pathways is a nuisance that you can avoid by putting a double layer of perforated landscape cloth over the pathway and covering this with a 2- 3″ layer of bark mulch or coarse sawdust. When laying down the landscape cloth, allow it to come up 1″ against the bottom board of the bed, and staple this to the bed. This will not be visible because the mulch will cover it.
When buying mulch, ask the seller if they have had any complaints about weed seeds in the mulch. It’s very common for bark mulch to have weed seeds that sprout in your pathways. Some weeds will still appear on your pathways regardless of the mulch. Wait until it rains before pulling them out or you might rip the landscape cloth. The weeds will come out easily if the ground is wet.
Can a raised bed be installed on a concrete surface, such as a patio? Yes!
Many beautiful raised bed installations are set on concrete surfaces, but there are a few things that need to be taken into consideration. Typically, patio and driveway surfaces are not level. This is intentional so water can drain away from the main house structure. Raised beds, however, should be built to level, the same as if being constructed on soil. This means the bottoms of the beds will need to be blocked up on the low end just enough to facilitate and direct drainage. To learn more about this, read our article:
Gardening on Concrete with Raised Beds and Patio Containers
The Best Soil for Raised Garden Beds
One of the benefits of raised bed gardening is drainage, but this feature also makes the soil requirements of your garden box a little different. You can fill your beds with your own yard topsoil, but if you want to give your plants the best chance, it’s a good idea to start fresh since you have an opportunity to prevent weeds. The following explores both options.
The Best Homemade Soil Blend:
- 50% screened topsoil made of healthy loam.
- 50% screened compost, which can be anything from your own compost, along with mushroom manure, animal manure, or fish compost.
The Best Premium Soil Blend:
- 1/3 peat moss
- 1/3 vermiculite
- 1/3 compost blend similar to the above
This last combination above will help eliminate weeds, but the real key to these combinations is the compost. No matter how great your topsoil is, your beds will fail dismally without compost, which will need to be added again every year. For more information, read our article about How to Build and Nourish Healthy Garden Soil.
Ongoing Soil Building Can Be Done in a Variety of Ways:
- The lasagna method: Fill the bottom of your garden boxes with a layer of leaves, grass clippings, straw, wood chips and other organic materials, with a layer of cardboard on top. Next, add your soil. This mixture will break down into rich compost over time.
- By planting green manures: Every couple of crops, plant a legume such as clover or field peas in your raised bed. When this matures, chop it up and dig lightly into the soil. Leave to rot for the following season.
- By adding more compost: Add any combination of organic composts to create a light, crumbly, fluffy texture.
How to Irrigate Raised Garden Beds
Types of Irrigation
There are many ways to water a raised bed. Each one has a variety of pros and cons.
- Drip Irrigation: A network of hoses with emitters or holes that allow water to drip out slowly.
- Soaker Hose: A porous hose that leaks or soaks water out along its entire length.
- Sprinkler: A device with holes hooked to the end of a hose that sprays water through the air.
- Hand Watering: Watering with a sprayer or other nozzle by hand.
- Wicking: Filling a porous reservoir under the soil that wicks water slowly into the soil, with a specially built garden bed or primitive olla pot.
| Irrigation Method | Price | Labor | Installation | Effectiveness |
|---|---|---|---|---|
| Drip | Relatively expensive | No work during watering | More work to install | Very precise, saves water, prevents disease |
| Soaker Hose | Relatively inexpensive | No work during watering | Less work to install than drip | Gaps possible, saves water, prevents disease |
| Sprinkler | Inexpensive | Some light work to move sprinklers | No work | Covers everything, including areas that may not need water |
| Hand | Very inexpensive | Time intensive | No work | Targets desired areas |
| Wicking | Somewhat expensive | No work | Lots of work to set up | Very precise |
Installing Irrigation
The goal of any irrigation system is to make sure every plant gets enough water to thrive. With each method of irrigation there is a different strategy to meet this goal: for dripping and soaking, hoses must be placed in the right locations to fully water the desired plants. Additionally, the holes in your drip lines must be spaced according to your plant’s needs.
When spraying, whether with a sprinkler or by hand, you must also consider duration. Adding an automatic timer to your watering system will help remove the guesswork. Even better, a raised garden bed makes irrigating your crops simpler because drip tape and soaker hoses can be mounted to the side of the box to keep them immobile. The most common mistake when irrigating is leaving gaps. Be sure to measure the reach of your hose against the size of your box and install enough lines to thoroughly soak the soil.
How Often to Water
If the soil is dry one inch below the surface, it’s time to water. Raised beds need to be watered a little more often than traditional, in-ground beds because they drain faster and tend to encourage rapid plant growth, which requires more water. In the summer, this might mean watering multiple times per day depending on the stage of plant growth and the type of crop. In general, it’s better to water deeply a few times per week than more frequent, shallow watering.
Should I Automate My Watering System?
Automation works best with a drip line or soaker hose system. Putting your hoses on a timer ensures that you won’t forget to water when your plants most need it, and saves your crop when you are vacation. Automating your system also allows you to time watering for the cool of the evening or the middle of the night when the evaporation rate is lowest. For more information about automating your watering system, see our article about The Absentee Gardener: How to water Your Vegetable Garden Without Being Home
Conserving Irrigation Water
If you are using drip tape or soaker hoses, you’ve already taken a big step towards conserving water. You can take this a little further by mulching on top of the hoses around your plants to further reduce evaporation. Routine maintenance of your system should also include checking for leaks, which are often caused by creatures looking for water (or errant pitchforks). You can prevent leaks at joints by making sure there is proper water pressure for the system you are using, and that all joints are sealed. It’s also a good idea to install shut-off valves for each bed or garden section so that you can choose to water some beds less when your growing season is winding up or down.
Raised Bed Watering Tips
The edges of the bed will dry out a little faster than the middle, so pay special attention to the location of your plants. If you are sprinkling or spraying, put a mug in your garden to see how many inches of water you are using. You can also place a container beneath one of the holes in your drip line to gauge how much water your system is delivering to each plant. See Drip Irrigation vs. Soaker Hoses: Which is Better for Your Garden?
