How to Build a Cold Frame for Vegetables

According to Samuel Ogden, a Vermont gardener of 40 years and author of "Step by Step to Organic Vegetable Growing", a gardener has three main uses for a cold frame: hardening off seedlings that have been started indoors for transplant, early planting of frost tender vegetables and as a bed for fall transplants that will carry through the winter. Whatever use you choose for it, a cold frame is useful when growing vegetables.

Things You'll Need

• Tape measure
• Surveyor's stakes
• String
• Cold frame sashes
• Level
• Cinder blocks
• Garden spade
• Well-rotted manure
• Garden soil mixed with compost
• Lumber 6 feet-by-2-by-4-inch
• Lumber 2-by-4-by-14-inch
• Lumber 2-by-4-by-30 inch
• Nails
• Hinges

Instructions

Construct the Walls

1. Select a location to build your cold frame. Remember that this is a permanent construction, so where you build it will be where it stays.

2. Measure out the cold frame dimensions and mark them off with surveyor's stakes and string. Allow 8 inches for the width of the cinder blocks.

3. Calculate how many cinder blocks you will need, according to the dimensions of your cold frame. Use cinder blocks that are 8-by-8-by-16 inches. You will need enough to make the front two rows high and the back four rows high. Add 18 cinder blocks for each side to come up with the total number of cinder blocks needed.

4. Excavate the area inside the cold frame dimensions to a depth of 16 inches and level the site.

5. Lay down the foundation row of cinder blocks, outlining the excavated area. Level this first row and set the bricks firmly. Ensure that the inside dimensions are equal to the dimensions of the sash to be used. Fill the cinder block centers with soil and tamp down firmly.

6. Construct the second row in the same fashion, by staggering the second row blocks with the first row blocks. The top of the second row should set even with ground level or slightly above.

7. Build the third row, staggered to the second row, but omit the front edge.

8. Add a fourth row of cinder blocks with only three bricks on each side, giving the sides a gradual incline.

Build the Frame

1. Fill the bottom of the enclosure with 6 inches of well-rotted manure. Cover that with enough nutrient-rich topsoil mixed with compost to come up about an inch below the top edge of the front wall.

2. Drive 2-by-4-inch posts into the ground at each corner, inside the cinder block wall, and at each sash juncture if you've opted to extend your cold frame with more sashes. Make the top of each post come to 2 inches below the top edge of the wall. The 2-by-4s for the back posts will be 30 inches and the ones for the front posts will be 14.

3. Use 6 foot 2-by-4s to create back, front and side sills, with cross supports at each sash juncture. Secure the sills to the tops of support posts with 16 penny nails.

4. Attach the sashes to the wooden frame with hinges along the back wall, with two hinges per frame.

5. Shore up the back and side walls with excavated soil.

Tips & Warnings

• You can buy 3-by-6-feet cold frame sashes at building supply stores so design your cold frame with these dimensions in mind. Increase the size of the cold frame by constructing a wider frame that will accommodate more sashes

References

• "Step-by-Step to Organic Vegetable Growing": Ogden, Samuel: 1971: pp.64-68.