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Building a Raised Bed Garden


5 stakes | twine | steel measuring tape | flour or lime

Note: this is a math lesson, too, so you might want graph paper and a pencil

Rototiller and/or garden fork, sod cutter, sharp spade and wheelbarrow

2 pieces of 2" x 12' lumber, 8" to 12" across

2 pieces of 2" x 4' lumber, 8" to 12" across

2 pieces of 2" x 2" lumber, 4 feet long, for stabilizers

Four 1-foot 2" x 2"s for corner supports

1 lb. of 10d nails, or 1 box of 3" galvanized deck screws

Hammer or screwdriver | carpenter's angle | pencil

Big piece of plywood or chipboard to pack the soil in

Iron rake | Hose

While it's clear that getting as many inches deep as you can of loose, fertile soil for your garden bed is important, it's up to you whether to build a lasagna garden with soil that is raised up from ground level but otherwise unsupported . . . or to build a container for your raised bed, to support your pile of several inches of good garden soil.

Most of the time, if the garden is visible from a house or school building, you'll want it supported because it looks neater.

Let's say you choose to build.

Nobody says raised beds constructed from wood or other materials have to be rectangular or square. But most are. However, for a kids' garden, it might be fun to pursue a triangular, round or other shape. Whatever you can imagine, if you can build it, it'll probably work.

You can purchase a gorgeous, ready-made container made out of cedar or "plastic wood" with fabulous, turned corners and tall sides. But that can get pricey.

You can line up some cement blocks, but some people think they're ugly.

The most practical and handsome solution might be to use lengths of untreated lumber, and let the length of the lumber dictate the size of your beds. For example, if you can easily get 8-foot lengths, then get three pieces, cut one in half, and build a bed that is 8 feet long and 4 feet wide.

Let's assume that you are making a new raised garden bed where previously, there wasn't a garden. Let's assume you can get 12' lengths of lumber. Let's have it end up 12' x 4'. Ideally, do this in the fall and add chopped-up leaves to the soil to let it rot into rich, fertile soil by spring. But it's OK if you choose to do this shortly before spring planting.

Most gardeners say that mentally, they don't like coping with a bed that's longer than 15 feet because those really long rows translate to really long work sessions.

Also, when working with kids who have shorter arms, you might not want to build anything wider than three or four feet, simply because it's hard for kids to reach much further than that, and you don't want them standing or kneeling on the garden soil because they'll compact it.

Experienced gardeners often settle on raised beds that are 15 feet long and three feet wide, with an aisle about three feet in between them covered with wet newspaper and clean straw, bark chips or free shavings from a nearby lumbermill, to give access from both sides of the bed.

To lay it out, first mow the area as short as you can. Leave the clippings in place: you'll be using them for organic power!

Tie twine to your first stake and push it into the ground for one corner. Measure 4 feet across from it, and put Stake #2 in place. Wrap twine around it, too. Don't cut the twine; just keep going from stake to stake.

Now measure five feet from Stake #2 and stick in Stake #3. Now you should have three stakes in place, forming a triangle, with twine between them that measures 4 feet at the base, five feet along the side, and six feet along the "hypotenuse." That's the "magic triangle" first noticed by the Egyptians 4,000 years ago.

The "magic triangle" principle of geometry holds that with a right triangle, if the first leg is 4 units (in this case, feet), the second leg will be 5 units, and the hypotenuse (which is the side of a right triangle that is opposite the right angle) will be 6 units.

Now that you know your bed is going to have right angles at the corners, put Stake #4 seven feet down from Stake #3 -- since that side will have a total of 12 feet (5 feet from Stake #2 to Stake #3 plus 7 more feet - 5 + 7 = 12). Wrap twine.

Now measure 16 more feet of twine - four feet for the end, and 12 feet for the other side. Tie the end of the twine around Stake #1.

Now you can go back put in Stake #5 and wrap twine. Finally, connect twine from Stake #5 back to Stake #1. You might have to adjust the position of Stake #5 in order to make the twine taut, and your design a perfect rectangle!

If you get confused, use graph paper and consider each square represents one square foot. That should help you see where to position your stakes.

You can sprinkle flour or lime to mark the area lined up by the twine, and remove the stakes and twine.

Now let's get the soil ready. First, edge the bed all the way around by pushing straight down with a straight, sharpened spade along the flour or lime line. (It's well worth your time to take your spade to the hardware store once a year to get it sharpened.)

Cut out blocks of sod, using the spade at a very low angle so that you remove only a thin layer. Turn them over so that the green doesn't show. Chop them into pieces with the spade.

Now, whether you use a rototiller or do it by hand, dig deep into the soil with the garden fork or spade and chop the sod into small pieces so that worms and microorganisms can break the grass and weeds down into fresh soil.

Loosen and aerate the soil to a depth of 8-10 inches. Try to get the sod evenly mixed into the loosened soil. Add a couple of bags of rotted manure, compost, leaves and more grass clippings if you can.

Now let's build the wood frame that will support the rest of your soil!

Screw or nail one end piece to one of the side pieces. Screw or nail the second side piece in the same way. Repeat at the other end to create a box. Use three fasteners for each corner. You can use a carpenter's angle to make sure the corner is square.

Measure and mark 4-foot intervals on each long side so that you'll know where to place your two stabilizers. Set them flush with the edge on each side, and screw or nail in place. They'll be at the top of your frame now, but you're going to be turning it upside down, so they'll be at the bottom in final position.

Now set your four corner supports at the inside of the corner and screw or nail in place from the outside, at both the end and the side.

Place it on the prepared soil. Loosen the soil inside with the garden fork.

You will almost always need additional soil and compost to fill each box. How much will you need? Compute it with the right-triangle method: depth times width divided by two to get the area of the triangle, then multiply by the length to get the volume of each box. There are 27 cubic feet in a cubic yard. Chances are, for the average sized box, you will need 2 or 3 cubic yards.

Spread compost and, if you wish, black topsoil, to within an inch or two of the top. Rake with an iron rake to break up any clumps. Pack it down by laying a big piece of thin plywood or chipboard on the soil and walk on it 'til you quit sinking. Kids love this part!

            Then add more soil and compress again.

            Rake again if needed. You can put in concrete block pavers in the middle as stepping stones for future planting, weeding and harvesting tasks.

Water in with a hose. Let settle for a week. Add more compost if you wish.

And there you are!

By Susan Darst • Projects 01 © 2010

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