A Beginner's Garden: How to Turn Your Raised Bed into a Greenhouse or Coldframe

"A Beginner's Garden: Soil Layers and Planting Your Raised Bed"

See related slideshow: "Use Your Raised Bed as a Greenhouse or Coldframe"

If you are using your raised garden bed early in the spring or late fall, you may want to add a plastic cover to provide plant protection from frost or severe weather. After your raised bed is level and filled with soil, but before you plant it, construct this simple plastic cover. This type of cover will withstand tremendous wind, rain and cold.

You will need:
• "Clear" construction plastic sheeting, heavy gauge 6 ml
• Heavy gauge wire, stiff enough to support a curved bend (9 gauge tension wire works)
• Electrical cable staples OR roofing/ large head nails
• Twine
• Tent stakes
• scissors, cutters, hammer

1. Push a tent stake into the ground outside each end of the raised bed.

2. Cut the wire into lengths you can bend into arcs over the width of the raised bed. Allow 12 to 16 inches extra to push into the soil. That gives you 6 to 8 inches on each side to push into the ground.

3. Bend the wire arcs and push the ends into the soil inside the raised bed frame. They look like croquet wickets.

4. Open out the plastic sheeting, and measure the length and width over the arcs. Allow an extra 12 inches at each end of the length for fastening. Allow plenty of width over the arcs to cover to the ground on each side of the frame. Cut the sheeting to size. Oversize it if you are unsure, and you can trim it later.

5. Gather one end of the plastic and tie it securely with twine. Wrap the twine 3 or 4 times around the gathers before tying. Slip the twine wraps under the hook on the tent stake to anchor the ends of the sheet in place. Repeat for other end, and adjust the placement of the stakes so the plastic is taut across the arcs, but not extremely tight. There should be some slack.

6. Nail an electrical cable staple to the outside of the frame, halfway between two of the wire arcs. Place a cable staple between each set of arcs on both sides of the frame. I use electrical cable staples because they won't rust. You could also use a roofing nail or other large head nail.

7. Tie one end of twine to one staple, and carry the twine over the plastic to the corresponding staple on the opposite side of the frame. Tie the twine just tight enough to anchor the plastic in place. Repeat for each set of staples.

8. Slide the plastic down over the wire arcs to close the cover. It will slip over the wire and under the twine, all the way to the ground outside the frame. Adjust the tension so the plastic slips up and down easily from both sides.

I use these covers very early in the spring and way past killing frosts in the fall. It turns your frame into a little greenhouse where you can set flats of indoor seedlings on nice days; you can easily move them back indoors if the night temps dip. Open the plastic as little or as much as you need to by sliding the plastic up from one or both sides, or slide it all the way to one side so it is completely open.

Moisture condenses inside these covers, which reduces evaporation, but I always open the edge of the plastic a few inches for air circulation on sunny days. Heat can really build up inside.

During the summer, I remove the plastic sheets and replace them with netting. Regular nylon netting from a fabric store is fine. Use it in more than one layer if you wish. The netting makes a great insect barrier, and it provides cooling, filtered shade for lettuces and spinach when the temperatures soar. The netting makes great shade in late August heat when I need a cool place to start seeds for fall crops like broccoli.

I also use this method to anchor "garden tunnels" directly in the ground for spring and fall plant protection. Use a tent stake to anchor the twine on each side of the tunnel, since you won't have any frame for staples. These covers are amazingly sturdy. Some garden centers carry double layer insulating plastic sheeting, and other (expensive) specialty stuff you might want to check out. I've thought about using rolls of bubble wrap, but never tried it.

Sources:
Personal Experience