How to Build a High Heat Greenhouse

Amateur horticulturalists face a battle to keep their plants healthy. In the South, plants are attacked by insects year-round. Up North, the challenge is the short growing season due to the extreme cold that can affect growing even into the middle of June during planting season.



Building a greenhouse capable of staying warm enough to keep the frost and bitter cold winds off the seedlings can be expensive if you use electric or gas heaters. There is a danger of fire as well with these options because you cannot obviously supervise your greenhouse during every hour of the day. There is a cheaper option.

Preparation of the Ground

• 1

  Mark off the area that you will need to begin construction based on the estimated square footage of your chosen greenhouse. De-sod this area and level it as much as is possible. You will need to have an area located to the side or rear of the greenhouse about the size of a small above-ground pool.

• 2

  Apply Triazicide to the de-sodded area. Typically the mix ratio is 2 oz per gallon of water. For this purpose use at least 8 oz per gallon of water. Fill the 2-gallon sprayer with water and saturate the ground, the corners and if there is any left over, a small area around the perimeter of the greenhouse location.

• 3

  Dig an approximately 18-inch hole at each corner of the location and then two 18-inch holes in between the two lengthwise sections. Insert one of the six foundation posts into each hole and secure with cement. The height of these foundation posts depends on the schematics for the greenhouse you chose. Eight feet high is recommended for many greenhouse plans.

Preparing the Heat Source for Your Greenhouse

• 1

  Take a 25-foot length snow fence, which is a wooden plank fence linked together with strands of wire, to make the shaping of the fencing flexible. Typically snow fences are anywhere from four to six feet high. Using this fencing, form a circle fence and latch together with baling wire or bungee cords. Create this structure right next to the greenhouse area as close as you can to the edge of the foundation posts.

• 2

  Line the bottom of the fence-circle with the 8mm plastic sheeting and staple the bottom of the plastic to the fence posts. Staple one end of the 8mm plastic sheeting to one of the snow fence posts on the outside of the fence. Wrap the fence circle with the plastic stapling the plastic to each snow fence post from the bottom to the top. Spray more of the Triazicide around the circumference of the fence circle.

• 3

  Fill the fence-circle with composting materials throughout the fall. To generate the heat you will need, you will have to have a combination of nitrogen and carbon. Grass clippings, weeds or alfalfa green hay will supply the nitrogen. Garden waste, chicken or pet droppings and organic garbage that you would normally toss will provide the carbon. Alternate the layers of leaves with layers of grass clippings or alfalfa meal or hay.

  Using a hose, spray down each layer as it is added. Excess water will find it's way out the bottom of the fence circle; this is normal. Keep the top of the pile of compost slightly damp through the fall.

Connect the Fence Circle to the Greenhouse Structure

• 1

  Finish the greenhouse construction according to the schematics you purchased. The wall that should be located next to the fence circle should an open space secured with 2 x 4s to allow the flow of air from the fence circle to the inside of the greenhouse structure.

• 2

  Staple one end of the plastic sheeting at least 8mm thick to the roof of the greenhouse structure. The rest of the plastic sheet roll should be stretched across the top of the fence-circle and down both sides. Staple this part of the plastic sheeting to the outside of the fence-circle.

• 3

  Using either sand bags or a wooden frame of 2 x 4s, secure the plastic sheeting as close to the ground as possible. There should be no portion of the area between the fence-circle and the greenhouse that is exposed to the outside air. Place a piece of Dura-Wall on top of the composting pile. The area just above the composting pile will typically remain at around 80 degrees throughout the year. This will be a good location for seedlings and the more sensitive plants. The heat generated by the composting pile will rise, and if the structure of the greenhouse is sound, will keep the greenhouse at a comfortable temperature all year long.