What is a raised garden bed?
But let's start with the scratch and definitions. When we say "raised garden bed" or simply "raised bed," we mean a free-standing box or frame - traditionally without a bottom or top - that sits on the ground in a sunny spot filled with good-quality soil. Raised beds are usually opened at the bottom so that plant roots can access soil nutrients below the ground.
Of course, a raised bed can be simpler than this: You can build a raised bed without a frame, just pile the soil 6 to 8 inches high and level the top. This requires no additional materials (other than soil).
Benefits of Raised Garden Beds
There are many reasons to garden on a raised bed.
They drain well and help prevent erosion.
They heat up early in the spring and give you a longer growing season because the soil above the ground heats up faster.
Raised beds allow you to control the soil you put in them, allowing for dense planting; plants that grow densely in a raised bed mature faster.
They prevent weeds from taking over because the beds are lifted away from surrounding weeds and filled with disease- and weed-free soil.
Since you're not walking on the bed, the soil isn't compacted and stays loose, eliminating the need for painstaking digging every spring. A raised bed helps keep things organized.
Garden chores become easier and more comfortable thanks to less bending and kneeling. Save your knees and back from the labor and pain of tending the garden!
Raised beds are great for small spaces where a traditional row garden might be too wild and unwieldy.
It is easier to separate and rotate crops each year.
Raised beds make square foot gardening and companion planting easier.
Depending on the height you make, a raised bed can even eliminate the need for bending!
Finally, the raised bed is attractive!
Choosing the Right Material for Your Raised Bed
You can choose to decorate your loft bed with whatever material you have on hand (wood, stone, brick, cement blocks). Stay away from painted or pressure-treated wood, which can leach chemicals or lead into the soil. Bricks can be placed end to end on the edge, or if you have enough bricks, they can be erected to create a higher edge for the bed.
Bury the bottom a little to stabilize them and stop weeds from slipping under and between the bricks. A few years ago, I was lucky enough to get plenty of roof slates and used them to trim raised beds on slopes. Cement blocks can be used to make beds for plants that like heat. Here is the list of possibilities:
untreated wood. Pine is the cheapest, but will rot after a few years, as will many untreated woods. Hemlock will last longer. Decay-resistant woods such as cedar, redwood, or locust will last longer; they are expensive. Cedar is preferred because it is both corrosion-resistant and durable, and can last 10 to 15 years. It is also insect resistant due to the oils in the wood. Reclaimed wood made from plastic bottles is also a bit more expensive, but lasts indefinitely. Another option is to simply opt for thicker, untreated planks. For example, a 2-inch thick larch plank will last ten years without treatment.
Modern treated wood contains chemicals that prevent rot. Unlike in the past, however, studies have shown that any leached compounds are within safe levels set by the EPA. Some gardeners are still uncomfortable with treated wood. For those concerned, one option is to line the interior of the bed walls with polyethylene.
Railroad sleepers (treated) are easy because you can simply place them on the ground and drive them with nails. Old railway sleepers treated with creosote don't seem to cause any health problems since most of the creosote has been lost.
Pallets can be an inexpensive source of garden bed material, as long as you know where they come from. Pallets were developed for transporting materials. Avoid trays that are also treated with methyl bromide chemicals, a known endocrine disrupting chemical that can affect your reproductive health. Most pallet manufacturers stopped using the chemical in 2005, but many old pallets still exist. Look for the "HT" or heat treated stamp on the pallet. If there is no stamp or you cannot verify the HT on the surface, please do not use the tray in your garden.
Concrete or brick can be used. However, keep in mind that concrete will increase the pH of the soil over time and you may need to modify the soil.
Composite wood is a new product made from recycled plastic and wood fibers. It is both rot-resistant and durable, but also very expensive.
Cinder blocks: The extra heat from concrete is great for Mediterranean-type herbs like rosemary and lavender. Their holes can be filled with soil mix and planted with herbs or strawberries. Each piece is 16 inches long and 8 inches high; the big box prices are the most reasonable.
Rocks and stones are plentiful in some areas and make for nice free edges. You can build beds around mounds that you have already started. Once it's closed, you can fill the sides with more soil and add compost, chopped leaves, fertilizer, etc. Rake the top flat and let it sit until next spring to be ready to plant.
The two beds below were built using Trex lumber from "seconds" piles from a local lumber yard. It's too twisty for building decks, but works well for garden beds. The bottom is lined with a 1/4-inch hard cloth screen to keep the voles from eating the precious bulbs.
How wide should a loft bed be?
Garden beds should be no wider than 4 feet so that you can enter the garden without stepping into the bed. Fortunately, wood is usually cut in 4-foot increments.
Stepping into the bed is taboo. It compacts the soil, making it harder for plant roots to get the oxygen they need. Making the bed too wide also makes the middle difficult to reach, which also makes weeding and harvesting difficult.
If your raised bed is built against a wall or fence, we recommend setting it to less than 4 feet (2 to 3 feet wide) as you can only access the garden from one side.
Length is not so important. You can make 4x4 or 4x8 or 4x12 beds. Feel free to do whatever you want, but I find it easier to make a few shorter beds than a very long one. Also, many crop families are best separated into beds.
How deep should a loft bed be?
Typically, the standard size for wood, such as cedar, is 6 inches tall. In other words, the dimensions are 2 inches x 6 inches x 8 feet. (Note that planks purchased at the lumber yard are actually 1.5" thick x 5.5" high.)
You can certainly go higher (18", 24", 36"), but be aware that adding the weight of soil will increase the pressure on the sides. You will need to add cross bracing to any bed over 12 inches tall.
Consider what you might grow. The depth of the soil itself is very important and depends on how much soil depth the crop needs in the ground. E.g:
Rooted crops like carrots, parsnips, potatoes, tomatoes, and squash require a soil depth of at least 12 to 18 inches. If the plant doesn't have this deep loose soil, the roots won't be able to penetrate deep enough for nutrients.
Shallow root crops (such as lettuce, vegetables, and onions) require a soil depth of at least 6 inches.
To be on the safe side, you just need to make sure the bed is 12 to 18 inches deep. No matter what height you choose for your frame, you will need to loosen the soil below the ground accordingly. For example, if you have a 6-inch high bed, we recommend loosening the soil in the ground an additional 6 to 9 inches if you want to grow root vegetables. This is not necessary if you are only growing shallow root crops.
loft bed location
The loft bed needs to be in a sunny location! Here are the requirements:
Most vegetables need 6 to 8 hours of direct sunlight ("full sun") a day, especially from lunchtime.
Level, level ground.
Proximity to house for easy weeding and harvesting
Do not place the bed in a windy place or in a frost bag.
The soil needs to be well drained, so avoid any wet or swampy areas.
Prepare the venue: Option 1 (Basic)
To make a basic loft bed, use string to outline where you want it to be. As above, keep it between 3 and 4 feet wide so you can still easily reach the center.
This will help smother the grass in the area, but if there is sod or grass, trim it short and dig it out, saving the clumps to one side.
Loosen the soil on the bed, turn the turf clumps upside down, scrape the soil from the outside path and add it to the bed, as well as any other amendments you wish to use to raise the soil level.
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Preparing the site: Option 2 (no excavation)
Some gardeners don't bother to dig sod. Because as long as one layer is thick enough, the soil will block the grass and weeds below. Gardener Charles Dawding, who created the "no dig" method. His philosophy is that digging brings more weed seeds to the soil surface, which leads to more weeds and more weeding. Digging also accelerates nutrient loss, so you need to feed your plants more often, and it rips apart the complex life and very structure of the soil, reducing its ability to drain and hold water properly.
Here's how to build a raised bed using the "no-dig" method:
Trim grass or weeds as close to the ground as possible. Then cover the area with cardboard, which can smother the grass/weeds and eventually rot into the soil. (Make sure you remove any tape and staples that won't break down.)
Make sure to overlap the cardboard/newspaper (about 6 inches) to make sure no weeds slip through the cracks. They'll reach for any sunlight they can find.
Add a thick layer of compost (4 to 6 inches) on top of the cardboard. This will be your growth medium.
After setting it up, you can immediately get on the car and plant it. By the time the root reaches the cardboard, it has already started to break down and the root will be able to search deeper beyond the cardboard layers.
The compost you add on top should gradually combine with the soil below through the action of worms etc. Each fall/winter, the beds need to be filled with fresh organic matter (an inch or two), which will help gradually improve the fertility and health of the soil, including below the raised bed. This means you should be doing well with rooted vegetables like root crops.
