How to Build a Base for an 8-by-6-Foot Greenhouse

Updated February 21, 2017

Most recreational greenhouse owners agree that there is something profound about the peaceful hours spent working in them. Many greenhouse kits and prefab options are available, and a popular size is eight by six feet. Many are made up of aluminium struts and specialised plastic windows and are lightweight, which makes them vulnerable to toppling in gusty winds. The solution is building a strong, steady base solidly anchored into the ground.

Stake out a stable, level location at least twice the size of the desired greenhouse location. Consider the patterns of sunlight throughout the year in your locale carefully, as well as trees that may block sunlight when their leaves are full. Also avoid areas that are prone to flooding or soaking during heavy rain. The higher and drier the spot, the better.

Level the perimeter of the base site carefully, but smoothly draw the middle up to about two inches higher than the perimeter. Screw the auger anchors into the ground to form a 76-inch square, with the anchors on each eight-foot side of the base placed 10 inches from the end of the base. Twist in each anchor so the top loop holes are about seven inches above the level ground.

Cut the plastic sheet into two eight-foot-long by six-foot wide pieces and smooth them down flat over the site, maintaining the slightly raised middle. Then lay out the four-inch blocks on top of it around the perimeter with one at each corner, two evenly spaced along the eight-foot sides, and one in the middle of each six-foot side. Tap all the blocks to form a level plane around the perimeter.

Build the base frame from the beams so the outer dimensions are 74 inches wide by 96 inches long. This means two of the beams should be cut to 68 inches to fit inside the eight-foot-long pieces. Use one seven-inch-long lag bolt to screw into the ends of the shorter pieces after pilot holes have been drilled. Finish off each corner with the inside angles, using four 1 5/8-inch high tensile square drive screws into the beams on each side of the angle.

Carefully lay the perimeter frame down on top of the blocks and square perfectly. Keep the blocks even with the outer edges of the frame. Drill half-inch holes through the beams to align with the middle of the augers' top loops. Bolt through with galvanised half-inch bolts and nuts, using a large diameter flat washer to pull the augers' loops tight to the frame.

Cut the galvanised heavy wire cloth to fit the spaces under the frame and between the blocks and tack in place. Fill the interior of the frame with eight inches of smooth gravel. Tamp and level it.

Consider optional concrete slabs or treated wood decking as a middle walkway after the plant shelves or tables have been installed in the greenhouse.


Building on dry ground greatly extends the life of this base. Use a long pipe to turn the augers more easily.


Greenhouses must have strong, deeply anchored moorings to resist wind damage and potential injury from flying debris.

Things You'll Need

  • 4 4-by-6-inch pressure-treated wood beams, 8 feet long
  • 4 30-inch earth anchor augers
  • 10 4-inch wide standard concrete blocks
  • 4 2-by-6-inch galvanised angles
  • Plastic sheet
  • Corrosion-resistant hardware
  • Smooth gravel
  • Aluminium gutter screening
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About the Author

Pauline Gill is a retired teacher with more than 25 years of experience teaching English to high school students. She holds a bachelor's degree in language arts and a Master of Education degree. Gill is also an award-winning fiction author.