How much food can you grow in a small greenhouse?
We have had some general inquiries from people wondering how much food you can grow in a small greenhouse. The first thing to know is that if you are new to gardening, having a greenhouse is like having a lab in your backyard. You are going to experiment, add or take away minerals, have failed projects and be surprised at the resiliency of nature. Now, we do not want to appear as alarmists in any way but thought others might be interested in knowing too so here it goes!
What can you grow in 8’ x 8’ greenhouse? (64 square feet) As you can guess, there are a few factors that will affect your yield including whether you heat the greenhouse or add additional grow lights.
Compare and contrast quick crops mixed with longer crops like tomato in a barely heated greenhouse: Micro-greens take a week or two, Topsi radishes grow in as little as 30 days and heads of butter lettuce are edible in 60 days in a greenhouse. Tomatoes take the whole greenhouse summer (8 months) as does basil but the empty space can be used for spinach once the crops are pulled in the fall even if the greenhouse is unheated after October.
Shoulder season varies with climate but with a little seasonal heat you could get several crops over the eight warmest months of greenhouse growing. A family would have trouble eating more than 2 square feet (1 tray) of pea microgreens per week on salads, omelettes or stir fry. If they devoted 4 square feet all summer to radishes and decided their family needed 2 heads of lettuce a week they would need another 8 square feet. With the extra space plant six climbing tomatoes (these tomatoes grow up) plus an assortment of green onions, basil and herbs to fill the extra 22 square feet over summer.
Deciding how to make the best use of your greenhouse is a combination of what crop you are growing and whether you heat your greenhouse. Spinach, for instance is planted after tomatoes are removed in the fall and without any extra heat, it sprouts by March and is edible before the tomatoes go back into the unheated or partially heated greenhouse in May.
So obviously, the first decision is whether you will heat your greenhouse to extend the seasons. If you heat it seasonally you can grow so much more. But the big decision is what do you want to grow? Imagine growing Walla Walla onions, Red spear broccoli and leeks. These crops take up to a year to grow to maturity. If you left 8’ for a narrow path down the middle of your greenhouse you could grow 32 walla wallas, 6 Red Spear broccoli and 44 Leeks in a year. You might have time for a quick crop of radish or cilantro before the next crop of broccoli is planted in June. This is possible if you heat so the ground does not freeze solid in winter. Not a very comforting thought for an onion served every 11 days, a few bits of broccoli in March and April plus 5 leeks a week for two months after 10 months of solid growing.
If you are satisfied with fast growing green onions instead of walla walla onions or spinach instead of slower growing Winter Broccoli, there are so many possibilities in an 8 x 8 foot greenhouse. The best advice is to grow what you love and grow the crops that take the least time to mature. Seed packets are helpful for timing. The variety Topsi radish (30 days) takes half the time than special varieties like Wasabi Radish (60 days). Growing shelling peas takes more room and three months to harvest compared to the similar-tasting microgreens (8-10 days.)
There are lots of choices for faster growing veggies and remember to rotate your crop too when the season changes.
For more great tips from Donna, visit www.donnabalzer.com.
You can also read Donna’s gardening books: No Guff Vegetable Gardening with Steven Biggs and her just released Gardener’s Gratitude Journal: Part Diary, Part Personal Growing Guide.