Preparing the Ground for a Greenhouse

It's important to prepare your ground correctly before you erect your greenhouse. Luckily, this isn't difficult to do with a few tips and pointers in this guide. Give yourself a good half day or so to get the ground just right then you'll be all ready to put up your greenhouse. You'll want to do this on a dry day, when the soil is workable.

Choosing A Site

Your greenhouse will do well almost anywhere in the garden, however choosing the best spot to put your greenhouse can be the key to success.

  • Full sun or partial shade.
  • Any aspect can do well. Orientate the greenhouse north to south if you would like equal amounts of sun on both sides.
  • Avoid putting it under trees. You'll get bird droppings, moss and algae on your greenhouse. Trees can also pose a risk of dropping branches and produce excessive shade.
  • Plenty of space around the greenhouse will allow access for cleaning, removing panels during hot spells and replacing any damaged panels if needs be.
  • Think about where you'll get your water from for your plants in the greenhouse. Make sure its near a tap or your hose pipe can reach. Better yet, make sure there's enough space for your water butts.
  • Choose a nice level spot for your greenhouse.

Bases

Select which base will be best suited to your needs for your greenhouse. There are pros and cons for each base so take the time to decide which one is best for you.

Soil

Level compacted soil is the cheapest option and also allows you to grow directly in the ground. There can be issues however with weeds and drainage.

Step 1: Mark out the area for the greenhouse with pegs and string. Make sure the corners are exactly 90 degree angles. Both diagonal measurements should be the same length, this will make sure it's square.

Step 2: Remove any turf, weeds and larger stones from the site. Level out the soil, raking soil into small deficits and using a spade to skim off lumps. Use a long spirit level to make sure the ground is level and even.

Step 3: Compact the soil down firmly by trading down firmly over the area. Correct any dips and double check the area with your spirit level.

Step 4: Dig out sufficient holes to accommodate your concrete blocks. Make sure each corner has a concrete block and another block every 2 feet along the length and width. All the blocks must be level with one another and level with the surface of the ground.

You can build your greenhouse on top of your base and secure it to the concrete blocks using suitable wall plugs, screws and washers.

Slabs

Laying slabs is a good option and allows for growing on staging or in grow bags. Drainage isn't an issue and it's easy to deal with any weeds that might come up between the slabs.

Step 1: Mark out the area for the greenhouse with pegs and string. Make sure the corners are exactly 90-degree angles. Both diagonal measurements should be the same length, this will make sure it's square.

Step 2: Remove any turf and excavate to a depth of 2.5 inches. Using a long spirit level, make sure the area is even, flat and level. If you fill in any deficits with soil, make sure they're well compacted down by trading over the area.

Step 3: Mix 1 part cement with 8 parts sharp sand to form your dry mix for the base (do not add water). Make sure it's well mixed and begin laying it onto your area to a depth of about 1.5 inches. Rake it out evenly then go over it again with your spirit level to make sure it's level.

Step 4: Starting in one corner, lay your slabs in rows. Using a rubber Mattel, gently tap the centre of the slabs to bed them down. Make sure they are level and butted right up to one another. Once you've laid all your slabs, double check they are all the same height and level. Brush your remaining dry mix into the cracks and gaps of the slabs.

You should now have a level and even slabbed surface, perfect your constructing your greenhouse on. Secure the greenhouse to the base using suitable wall plugs, washers and screws.

Concrete Pad

A concrete pad will provide the sturdiest base for your greenhouse. It's a more expensive option but will allow for a permanent area for your greenhouse to sit on. Standing water can be an issue with concrete bases in the winter so be sure not to over water in the cooler months.

Step 1: Dig out an area the size of your greenhouse, adding 12 inches to each side. ensure the base of this area is smooth and level. Check the area is square by measuring both diagonals, ensuring they are the same length.

Step 2: Using 3-inch boards, construct a wooden frame the size of your greenhouse, adding 8 inches each side. place the frame in your dug-out area. hammer in wooden pegs along the outside of the frame. attach the frame to these pegs, once again making sure the frame is level and square.

Step 3: Create a mix of all-in-ballast and cement at a ratio of 5 parts ballast to 1 part cement. Completely fill your frame with the concrete, tamping it down as you go. Ensure the corners are sufficiently filled and tamped down.

Step 4: Using a length of wood longer then the width of your frame, tamp down the concrete from one end of the frame to the other. This process will be easier with one person either side of the frame. Ensure the concrete is completely level across your frame. Allow to dry slowly for several days.

Once your concrete has completely dried, you can construct your greenhouse upon it. Be sure to fasten your greenhouse to the base using suitable wall plugs, washers and screws.