build a raised bed, from Sunset Magazine’s basic structure (sunset.com/garden/perfect-raised-bed) to less formal beds made from recycled fencing. Sunset’s raised bed uses corner posts, but some gardeners prefer to reclaim those precious inches of growing space taken up by posts and build their beds without them. Either way, if you build your bed with materials that last, using a few helpful tips offered here, you will be able to enjoy your raised beds for years to come.
• Build on a level surface—It seems like a no-brainer, but you’d be surprised how many people try to assemble their raised beds in the garden among the foliage. Do yourself a favor and build the beds on a concrete patio or other level surface and then move them into place.
• Use deck screws—It will save you time (and maybe even a trip to the emergency room) to use 3-inch (7.5-cm) galvanized deck screws or stainless-steel screws instead of nails. Predrill your holes if you are working with materials like Trex® decking, which splits easily near the ends.
• Put the ugly side in—Lumber has an ugly side. It always does. Whether it’s a knot, a crack, or the neon-orange spray paint the company used to mark the product, you are likely to find flaws in the wood. Be sure to situate that flawed surface to the inside of the raised bed, where the soil can cover it. While you’re at it, check the wood for splinters or rough edges and point the roughest edge to the ground. This saves you the time and effort later on of either pulling splinters out of your thumb or sanding down your new bed.
• Hardware cloth, not chicken wire—If you have burrowing animals in your
neighborhood, there is one important step to take as you build your beds: line the bottoms securely with hardware cloth (welded wire mesh). Chicken wire is thin, and gophers can chew through it, but 1/2-inch (1.25-cm) hardware cloth will last for years and put your concerns to rest before you’ve even added soil to the beds.
How to Build a Raised Bed
1.Cut pieces of 2- x 12-inch (5- x 30.5-cm) lumber to the appropriate size. For a 4- x 8-foot (1.2- x 2.4-m) raised bed, purchase three 8-foot (2.4-m) pieces of lumber, and then you will only have to cut one board in half. Your beds will have an external dimension of 4 x 8 feet (1.2 x 2.4 m), but your internal dimensions, the actual growing area, will be slightly smaller.
2.Align the pieces vertically and bring the corners together as shown (see the diagram) on a level surface. Predrill the holes as needed and connect the corners with three 3-inch (7.5-cm) deck screws per side.
3.Once the frame is assembled, flip the bed over and attach hardware cloth to the bottom edge (if you are using hardware cloth) with 1/2-inch (1.25-cm) construction staples. Return the bed to the right side and position it in the garden.
4.Check the bed with a level to ensure that the foundation is…well, level. If your bed is sloped, water is likely to drain unevenly, and you may experience pooling in low areas.
5.Next, use a mallet or hammer to insert the 18-inch (46-cm) predrilled flat steel stakes against the inside walls of the raised bed. Place the stakes 2 feet (61 cm) apart. These prevent the wood from twisting or bowing under the weight of wet soil. It also prevents the bed from shifting over time, especially if you are building taller beds with several layers of wood. You will need to adjust the length dimensions of the stakes if you build taller beds. For a 12-inch (30.5-cm) bed, 18-inch (46-cm) stakes are appropriate. Hammer the stakes into the ground so that the top end of the stake sits about 1 to 2 inches (2.5 to 5 cm) below the top edge of the raised bed. You will not be able to see the stakes once the bed is filled with soil.
6.Secure each stake to the wood frame with four 1½-inch (3.75-cm) wood screws as shown (see “Metal stake placement inside front view” on the diagram). If you plan to attach a sitting rail or cap to the top edge of your raised bed, this is the time to do it.
7.Congratulations! Now you are ready to fill your bed with soil.
8.If you don’t have enough existing soil and compost to fill your raised beds, you will need to start off with bagged nursery planting mix, bulk organic vegetable garden soil, or a combination of ingredients. Once the beds are established, regular composting will keep you supplied with soil amendments.
A Formula for New Raised-Bed Soil
Before we get started, let’s get something straight: there’s no actual soil in potting soil. It’s a misnomer. Potting soil is usually made up of decomposed organic matter, like compost, wood chips, lumberyard waste, and peat moss. It also has perlite—that white puffy stuff that looks and sounds like Styrofoam when you crush it. Perlite is puffed volcanic glass that allows water to flow better through the soil medium. It doesn’t hold nutrients or add nourishment to the plants. It’s simply there as a placeholder for air and water.
Peat moss is widely used in potting soils to hold moisture and improve soil texture. It is acidic and can help adjust alkaline pH when needed. The trouble is that peat moss is a natural resource that is being depleted around the world. It takes about 3,000 years for nature to make a peat bog, and we’re using it up faster than it can reproduce. As an alternative, some forward-thinking soil companies are starting to incorporate a peat moss substitute into their potting soils instead. That alternative is called coir. It’s mispronounced by most, but the correct pronunciation (in English, anyway) is “coy-yer.” Coir works like peat to hold moisture and improve soil texture, but it’s made from a waste product, so it’s renewable.
Coir is made from the outside hull of coconuts—the part that is thrown away. The raw product has a high salinity, so it must be thoroughly rinsed before use. Thankfully, most manufacturers producing coir for the hydroponics industry are meticulous in eliminating salts before packaging the product. Investigate your provider before using a new material and inquire with your nursery professional about carrying coir-based products for your neighborhood.
That bag of potting soil from the store will probably say “organic,” but know this: there is no regulation about the use of the word organic in soil amendments. When we go to the grocery store and buy organic produce, we know it has been grown without pesticides and chemical fertilizers according to United States Department of Agriculture (USDA) organic standards. In the world of soil amendments, organic simply means “of, relating to, or derived from living matter.” Keep this in mind as you read about fertilizers as well.
So now that you have an idea of what’s in those bags, let’s talk about how to make your own raised-bed planting mix. Here’s the formula: start with 50 percent compost, 40 percent coir, and 10 percent perlite or vermiculite, depending on your existing soil conditions. Vermiculite does the opposite of perlite. It is a puffed mineral that is exploded like popcorn. It holds water like a sponge, which helps sandy soils retain moisture. It doesn’t break down, so you need to apply it only once. Vermiculite has a checkered past: at one point, a major mining source discovered that their vermiculite was contaminated with asbestos, but OMRI (Organic Materials Review Institute) put regulations into practice to ensure that each batch is now certified asbestos-free before sale.
You can also throw in coffee grounds and organic fertilizer if you like. This is just a starting point, however. If you mix in some of your existing soil, you will want to adjust the percentages a bit. If you have clay soil, add more compost to break up tight particles. If you have sandy soil, use more coir to hold moisture better. Play around with this. It’s all part of the experiment of gardening.
Now, to calculate your soil needs. If you have a raised bed that is 12 inches tall, it will be easy to figure out how much planting medium you will need. It’s simply length x width x 1 = cubic feet
