Determining how large a greenhouse you will need comes down to 2 questions:
- How much is going into it?
- How much will it cost?
The trick is finding a greenhouse that will hold all your plants and not break your budget. When factoring in costs, the purchase price is only the beginning. Most greenhouses don’t come with any extras. Things like benches, automatic vents, foundations and even heating systems are all extras.
You may also want to have your greenhouse wired for electricity and water. Then there are the ongoing charges for electricity, heat, water and general maintenance. Your plants can become as expensive as caring for your kids.
Greenhouse plants can also be as demanding of your time as kids. Unless you have automatic heat, venting, and watering, you will need to tend to your plants every single day. Seedlings in a greenhouse environment dry out very, very quickly. And they will not tolerate either overheating or a sudden loss of heat.
How Much Space to Plants Take Up?
The shape of your greenhouse will determine how much you can fit into it. Make sure you can move around comfortably in the greenhouse you’re considering. Some greenhouses shave costs by having sufficient headroom only in the peaked center area. (A tall greenhouse can actually save you money in the long run because it’s more efficient to heat and ventilate.)
Seed starters can get away without benches, if absolutely necessary. Flats can be grown on the ground, but your back will suffer. You can use any old bench or table, but greenhouses that have custom sized benches will make more efficient use of space. The average flat is about 10" W x 20" L. So a 6' x 2' bench will hold only about 7 flats.
You’ll also want some work space and storage space for soil, hoses, watering cans, etc. Additional shelving above is useful for holding light supplies like cell packs and fertilizer.
Remember that your plants will grow. That compact space you used to start the seeds will triple when plants are potted up. A 10' x 10' greenhouse is usually the minimum size for gardeners serious enough to need a greenhouse. But even a 6' greenhouse can be a treat to a gardener with cabin fever. You’ll just need to exercise some discipline.