Posts Tagged ‘planting beds’
While this post is part of a series that explains how to build your own raised planting bed, you could save much aggravation by assembling a planting bed from a kit. As you might expect, a kit costs more than twice what you pay for materials to build it yourself. Still, if you have absolutely no woodworking skills (or tools), seriously consider getting a kit. Follow this link for more information.
There are few limits to how you design a small kitchen garden. Once you’ve decided on location, you face the considerable challenge of designing and creating planting beds. So far, this blog has shown how to cut a planting bed into an existing lawn, and how to build retaining walls using landscaping timbers for a raised bed that sits five inches above an existing lawn—or another area with soil that can become part of the planting bed.
What if the soil in your future garden area simply isn’t usable? Or, what if there is no soil, but you happen to have a concrete pad left over from a demolished barn, house, garage or carport? Or, what if you just don’t want to bend down so far to reach the plants and weeds in your planting beds? These are all reasons to build deep raised bed gardens. This post explains how to use lumber other than landscaping timbers to build deep raised beds.
Small Kitchen Garden Raised Beds
In an earlier post on building raised beds, I suggested that at the very least, your planting beds should have soil to a depth of one foot. Were I to build on a surface through which roots couldn’t grow, I’d make my raised beds 14 inches deep. This way, I know that if I need to dig with a shovel, I won’t likely strike bottom when I push the shovel down with my foot.
Construction-grade lumber is typically milled from white pine trees. The wood is light-colored and light-weight, and it rots easily. If you build retaining walls for a raised bed garden from white pine, you’ll likely need to replace them in four-to-six years. Find a leech-proof, non-toxic sealant, and apply several coats before installing your raised bed.
You need to create a retaining wall to hold that much soil in a pile. Typically, people use lumber to build retaining walls, but there are many other fine alternatives. The downside of using lumber is that it has a tendency to rot; a wooden retaining wall in contact with soil can lose integrity in three or four years. Worse: in many climates, putting wood in contact with soil is like putting up a welcome sign for termites. If your planting bed will be close to your house—or snuggled up against it—take extreme caution not to provide a bridge for termites to get from the soil in your yard to the wood frame of your house.
Lumber for your Raised Beds
Termites and other agents that destroy wood have preferences. The most affordable lumber, for example, is pine, a very soft wood. Pine absorbs and holds water easily which leads to cracking and deterioration especially where the wet wood freezes, thaws, and dries out over the course of a year. Boring insects can make holes in pine easily, and microorganisms that cause rot find pine an easy target.
Hardwoods resist rot far better than pine does, but they are also considerably more expensive. To boot, hardwoods aren’t as easy to find in the same variety of dimensions as pine… and the very most rot-resistant hardwoods may simply not be available at all.
There are several varieties of cedar. You often see red cedar lining linnen chests and saunas, and white cedar used to build outdoor furniture and fences.
Cedar is a popular choice for building raised bed retaining walls. As it’s also popular for building decks and outdoor furniture, it may be available in a local store… but it is expensive.
Because it’s inexpensive and abundant, many people use pine to build raised bed retaining walls. But if you use pine, you’ll need to replace it every three-to-five years unless you treat it with something to protect it from rot. This is where the worlds of evil corporations, government regulation, an overzealous legal system, and fearful consumer gardeners intersect.
Pressure-Treated Lumber for Raised Beds?
From pre-history, people have turned to chemicals to protect wood from rotting. Creosote has proven extremely successful—it’s on telephone poles and railroad ties all over the United States. For many years, you could buy creosote-soaked railroad ties to build retaining walls in your own yard… but this has fallen out of practice: creosote protects wood effectively because it has stuff in it that’s really bad for biology. We have a lot of biology going on in us, so we shouldn’t be getting into creosote.
Pressure-treated lumber typically has a green tinge to it. If you use it in your garden, wear a dust mask when cutting it. Thoroughly clean up any sawdust you create and put it out with the trash. Don’t burn or compost unused pressure-treated lumber.
The lumber industry has found alternatives to creosote, and in most places you can find pressure-treated lumber that is extremely resistant to rot. In the United States, until recently pressure-treated lumber had arsenic in it, and experts have argued the danger of coming into contact with such lumber. About 20 years ago, I read a discussion in which an expert explained that if you collected the soil around a piece of pressure-treated lumber and ate it, you might consume a dangerous amount of arsenic after twenty or thirty years of daily consumption; even within an inch of pressure treated lumber in the ground, there was no detectable arsenic.
Despite these types of findings, all do-it-yourself gurus warned people not to use pressure-treated lumber where humans might come in contact with it. You certainly wouldn’t use it in a produce garden. And, because of lawsuits and finger-pointing, the industry agreed to stop putting arsenic in pressure-treated lumber destined for home use. In the US, a ban went into effect five-or-six years ago.
Does this mean you can use today’s pressure-treated lumber to build raised planting beds in a small kitchen garden? There’s still a lot of paranoia; but, living in the United States, I’d do it. To address any discomfort you might feel about it, there are two precautions you can take:
- After assembling the retaining wall, line the inside of the wall with heavy plastic before you fill the frame with soil.
- Stain or paint the surfaces of the retaining wall that face out or up; if you’re going to come in contact with the wood, paint it to lock in whatever chemicals are in it.
Here’s a terrific article about pressure-treated lumber, in case you want a thorough understanding about what was wrong with pressure treated lumber when it was made with arsenic: Does Pressure-Treated Wood Belong in Your Garden?
Plastic for a Small Kitchen Garden?
With the near necessity that every new house includes a deck, the building industry has introduced several materials to replace and out-last wood. Composite materials are waste wood—sawdust, for example—mixed with synthetics such as plastic and then formed into boards. These boards have the same dimensions as certain standard cuts of lumber and they have similar woodworking characteristics. That is: you can cut them with a saw, drill holes, and hold them together with screws. They’ll also take paint, though they don’t require any. Best of all: they’ll last for 40 or more years with no maintenance.
I’ve also read about “plastic lumber” which I can only guess is not a composite, but is plastic shaped and textured to resemble boards. If you don’t object to surrounding your garden with plastic, then composite decking is the most maintenance-free material for building a classic “wood-frame” raised planting bed.
I visited a home improvement store so I could estimate the costs of materials for raised planting beds using different materials. Here’s a summary:
|Retaining Walls Cost of Materials for 4′ x 10′ Bed
These estimates assume a 4 foot by 10 foot bed with 14 inch sides (technically, they’ll be 13 inches when assembled)… except in the case of the composite materials. The dollar amount in that column will build a 12-inch-deep raised bed.
One other caveat: I haven’t included costs for paint or sealer or plastic sheeting. If you build with untreated pine boards, figure to spend another $15 to $25 for sealant to protect the wood against moisture. I’d apply several coats of marine spar varnish to all the wood before assembling the retaining wall. That should extend the life of the walls for a few seasons.
Enough about Lumber
At this point, you have a pretty good idea of the materials you might use to make a traditional raised bed for a small kitchen garden. In an upcoming post, we’ll list materials to buy and the tools you’ll need to do the work. We’ll also explain how to assemble a frame and set it in place.
Several of my recent posts explained how to plan and build a small kitchen garden. Most recently, I showed the simple steps to create a planting bed in an existing lawn. In that discussion, A Small Kitchen Garden In Your Lawn, we got as far as removing sod, but we didn’t actually prepare the underlying soil for planting. Before we do that, let’s talk about alternatives to cutting garden beds into your lawn. Let’s talk about raised bed gardens.
Materials for my raised bed garden are minimal: landscaping timbers and 12 inch twisted spikes. There’s a lot of fuss about pressure-treated lumber leaching poison into the soil… and a lot of fuss that such leaching is negligible or non-existent. My raised bed retaining walls are of pressure-treated lumber, as are my tomato stakes. I’ll report in this blog when my health deteriorates as a result. If you fear leaching, use untreated lumber—something that rots slowly such as black locust. If you buy construction grade lumber, find a stable sealant and coat the lumber heavily before installing it. Perhaps four or five coats of spar varnish would extend the life your raised bed retaining walls for several years.
Raised Bed Gardens
Landscaping timbers are about 2.75 inches thick and 3.75 inches across. With rounded sides and flat tops and bottoms, these timbers stack easily. Their weight holds up well against pressure from your garden soil; they don’t bend easily. If you have your timbers cut to length at the lumber store (most will do this without extra charge), you need only a hammer and a drill with a long bit to assemble your retaining wall. If you buy timbers at full-length, you’ll also need a saw to cut them. (I’d use an electric saw, but the hand saw asked to be included in this photo.) For each rectangular bed you need four timbers of matching length for the length of the bed, and four of matching length for the width of the bed. For example, to create a planting bed six feet long and four feet across, you’ll need four 5’ 8.25” sections, and four 3’ 8.25” sections.
A raised bed is a planting bed that is higher than the existing ground. There are several circumstances in which you simply can’t grow fruits and vegetables in the ground in your yard. In those circumstances, if you want a small kitchen garden, you have only two choices: plant in containers, or build raised planting beds.
But a raised bed provides benefits beyond relief from poor site conditions. A raised bed…
- …can reduce the amount of bending to work a garden bed
- …creates a barrier between your planting bed and potential invasion of unwanted plants that propagate via roots, rhizomes, and stolons.
- …can protect the soil from becoming compacted and in so doing reduce the amount of work needed to keep the soil productive
Strategies for Building Raised Beds
There are no rules for building raised planting beds. Because we’re talking small kitchen garden, you may be trying to cram a planting bed into a very limited, and perhaps oddly-shaped space. In many cases, the shape of that space will dictate how you build your raised bed garden. If you’re lucky enough to have at least some open space in which to work, you’re a little less constrained.
At its simplest, a raised bed could be no more than a heap of soil sitting on the turf, on an old concrete slab, or on just about any surface. However, when the heap has no barriers to hold it in place, it will flatten out from one season to the next and require regular rebuilding to keep it together.
Because of this, most gardeners build walls to contain the soil of a raised planting bed. Those walls might be wooden boards, concrete blocks, brick walls, or cleverly-placed rocks. The walls must be strong enough to withstand pressure from hundreds of pounds of soil. Also, the walls should be durable; if made of unprotected wood, they may rot away in a matter of three or four growing seasons.
The Raised Bed in My Small Kitchen Garden
My house came with what looked like a planting bed for a kitchen garden (along with many beds with ornamental plantings). This was a raised bed 13.5 feet square. I don’t know how the previous owner created the bed, but it seems likely to have been a three-step process:
You’ll be stacking the timbers two deep around the perimeter of your new planting bed. Start by laying out a rectangle according to the scale model in this photo. (Yes, I simulated the layout of your landscaping timbers using Popsicle sticks.) Drill holes through the timbers to accommodate the spikes. The drill bit should be the same diameter as the spikes, or a smidge larger; for my spikes, I needed a three-eighths-inch bit. Put holes about two feet apart, but at this point don’t put holes in the last four inches of the outer ends of the timbers.
First, I believe the bed’s creator cut out a square of sod following the procedures I illustrated in my previous blog post.
Second, the bed’s creator built a retaining wall around the excavated square using gardening timbers.
Finally, the bed’s creator added topsoil and tilled—mixing the added topsoil with the “Lewisburg Soil Clay” he or she had found under the sod.
In fact, it’s possible that the previous homeowner had intended to have an in-ground planting bed, had cut the sod, and had then realized a problem… and there were two obvious ones:
- Most of my lawn sits on clay. It’s amazing that grass survives in it.
- The garden bed is at the bottom of a hill that drains my neighbor’s yard. Any depression at the bottom of that hill fills with water during rain. Perhaps the former homeowner cut out sod for a planting bed, watched it become a wading pool in a damp growing season, and then converted it into a raised planting bed.
How Deep Your Small Kitchen Garden Beds?
The illustrations in this post show how I would build a raised garden bed to match the one that was in my yard when I bought the house. You can follow these steps to build beds of just about any dimension—though it’s easiest to build rectangular planting beds this way. But there’s an important consideration we haven’t yet discussed: how deep will your crops grow?
Make sure the timbers are in the right places, and drive spikes through the holes into the ground as far as they’ll go. (If you’re looking for a perfect rectangle, measure both diagonals and adjust the frame until the measurements are equal.) Then lay the second tier of timbers on the first, overlapping pieces at each corner as these photos illustrate. Drill holes. This time, align a timber as you want it and hold it in place as you drill through it and the timber beneath it. Drill a hole at a corner first, drive a spike through it, move about two feet along the same timber, drill a hole and set a spike, and so on. If you don’t maintain alignment of the timbers when you drill holes, setting the spikes can be quite difficult.
Most vegetables that produce above ground tend to have shallow roots; they’ll be comfortable in four inches of soil. Even some foods that develop in the soil, such as radishes and beets, do so near the surface. Root crops such as potatoes and sweet potatoes can make it in six inches of soil, but you may need to mound soil on top of exposed tubers that push to the surface—this can happen even in very deep soil.
Depending on the variety you choose, long tap root vegetables (carrots and parsnips, for example) provide the deepest challenge: some want to grow ten or even twelve inches deep (though there are many varieties that tend to be shorter). So, for greatest versatility, I suggest that your raised planting beds provide at least 12 inches of soil depth.
The inside corners of your retaining wall will look like this. When you’ve spiked all the timbers to each other and the ground, you’re ready to prepare the soil. We’ll talk about that in an upcoming post.
Here’s the trick: if your raised planting bed will be on existing soil, you might be able to include some of that soil in your measurement. So, on an existing lawn, you could build a bed four inches deep, and till down some ten-to-twelve inches, using six or more inches of the existing soil for planting.
That’s the situation in my yard: my raised bed provides only about three inches elevation above the surrounding soil, so my plants’ roots can still reach excess moisture that collects from the hill above my garden. If this becomes a chronic problem, I can add another two inches of soil before I’d need to build the walls of my raised bed higher.
In an upcoming post, we’ll explore other ways to create walls for a raised planting bed. As well, we’ll talk about soil amendments that might be necessary to prepare your garden beds for spring planting.
Here are some other posts about building raised planting beds:
Our Raised beds on Gardencentre TV « The Recycle Works Blog – We thought you might like to see this video of our raised beds being reviewed on Gardencentertv website. It shows both how easy the raised beds are to assemble and how versatile they are. They say a picture can say a thousand words …
Innovative Raised Beds – So instead of writing a longer post, I thought I’d share a photo of my traditional raised beds built from recycled cedar fencing (top) and some alternative raised bed ideas I discovered at The Garden …
Making a Raised-Bed Garden – Back in 2002 when we landscaped our yard and started our garden we decided to create a raised bed garden. We decided on raised bed gardening for a number of reason. The main reason being the soil in our yard seemed to be composed of …
Perrenials fill two traditional farmyard planting beds: asparagus on the left and raspberries on the right.
I can’t tell you exactly how to build your small kitchen garden. That’s because I don’t know exactly what conditions you face as you make your plan. There are a few design considerations to have in mind as you make decisions about how to build your own planting beds.
How Big Your Bed?
Forget, for the moment, the soil conditions at the location you’ve chosen for your new planting bed. More importantly: how much space are you going to convert into a small kitchen garden?
A square that is 10 feet by 10 feet can hold 7 crowded rows of vegetables with 18 inches between rows. For plants that require little space—radishes, beets, carrots, lettuce, spinach, peppers, and beans, for example—you can get away with such crowding… but you’ll be wiggling between rows when the plants are full-grown.
You might crowd larger plants such as tomatoes, broccoli, cauliflower, potatoes, and sweet potatoes, to two feet… but again, you’ll be hard-pressed to find places for your feet when you’re in the garden.
Do You Need to be In Your Garden?
Here’s the key question in choosing a layout for a small kitchen garden: Do you need to be in your planting beds? A traditional vegetable garden on a country farm is a ploughed area in the yard. If it runs 100 feet by 30 feet (modest for someone to live off of year-round), then someone needs to walk in it to till it, plant it, weed it, and harvest from it. But, if you’re going small, perhaps you should design a garden with planting beds in which you never walk.
Walk Versus No-Walk Planting Beds
Here are characteristics of planting beds whose management requires that you walk in them. I’ve color-coded the characteristics where green=advantage, yellow=neutral, and red=disadvantage:
- They are generally more than three or four feet across at their shortest dimension
- You can easily use a power-tiller to turn the soil and mix in amendments.
- The soil gets compacted from regular traffic
- You must reserve tilled areas between planting areas where you can stand and walk while working the garden. This significantly reduces yield per square foot of tilled earth.
- You must manage the open spaces to keep down weeds
- There is enormous flexibility for how you arrange crops in the garden and for how you rotate crops from year-to-year.
- For the same total square footage of planting beds, it takes less fencing to protect a single large bed than to protect multiple smaller beds
Here are characteristics of planting beds you can manage without ever walking in them:
- Beds are no more than three to four feet across—two feet across if you can access them from only one side.
- A small kitchen garden of no-walk beds typically has several adjacent planting beds with room to walk between them and work them from all sides. If multiple beds aren’t an option, then a long, narrow bed provides the most versatility for rotating crops from season-to-season.
- For equal areas of tilled soil, you need far more space for no-walk planting beds than for planting beds in which you walk… but remember: you can grow far more per square foot in a no-walk planting bed than in one where you must walk to work the garden.
- Without someone pressing down on it, the soil doesn’t get compacted quickly. That makes it easier to work when you’re amending, planting, and weeding.
- Areas between planting beds can be lawn, permanent mulch, paving, or other easily-maintained surfaces.
- A no-walk bed can support far more plants per square foot than a large planting bed can. Consider: In a bed that’s only 18 inches wide, you can plant a row of vegetables near each boundary of the bed—you don’t need to get between the rows.
In a traditional in-ground planting bed, it can be difficult to distinguish where the yard ends and the garden begins.
Cutting-in a Planting Bed
I’m sure I’ve overlooked several notable characteristics of both walk- and no-walk planting beds. Please chime in if you want to share pet peeves about your planting beds, or identify advantages I’ve missed.
My next post will explain (with photos) how to lay out and cut-in a traditional farmer’s-style planting bed in your yard. In later posts, we’ll talk about differences between these traditional in-ground planting beds and the somewhat more European raised beds.