What information is helpful on greenhouse gardening in Maine?


I am wondering if there is any information on greenhouse gardening in Maine specifically a planting schedule for later harvest.


Jonathan Foster, Special Projects Assistant

Greenhouse gardening in Maine is a broad topic, ranging from backyard cold frames to huge commercial operations. Because this is our home horticulture site, I’m assuming you are looking for information on the home gardener front and not from an industry perspective (in which case I would refer you to our UMaine Cooperative Extension list of associations for better points of contact, like MELNA or MVSFGA).

You will want to take a look at this impressive page on hobby greenhouses from the UGA Extension–while it is written from the perspective of a Georgia gardener, it’s a great guide when making your plan. UMaine Cooperative Extension also offers a great resource, Bulletin #2752, Extending the Gardening Season, which has a bit of info on smaller greenhouses (as well as excellent info on other techniques than greenhouses). But the basics of greenhouse growing are pretty straightforward–the enclosed space provides a warm, humid, bright environment that persists even after the weather has killed off everything else outside. It’s an outstanding tool for extending your growing season, but because you’re creating an enclosed environment, it needs a bit of monitoring and active management.

As you’ll read above, if you’re still looking at purchasing or building one, it’s a great time to think about things like where you want to site it (long wall facing south for maximum sunshine in Maine), whether your want to plant in-ground or put in raised beds or growing benches, what type of material you want for walls (roughly–glass is great for light, less so for insulation, polycarbonate is the other way around), how big you want to make it (small is manageable for starters, but may be tough to expand if this really takes off for you), how close your access to water is and if you want irrigation, etc. It stays surprisingly warm in a good greenhouse, and in fact can become surprisingly HOT at any time of the year other than deepest winter, which is why having some ventilation system (even if it’s just window panes, roll up sides, or an open door) is essential.

At some point down the road, another source you might check out is this article on greenhouse pests from Dr. Colin Stewart and MOFGA–it’s pretty technical and aimed at more commercial operations, but the basics of pest management and the likely culprits you may encounter are the same. Because of the still, moist air, fungal problems are common issues in greenhouses, along with thrips, whiteflies, and aphids. I also always refer folks to the UMaine Cooperative Extension Planting Chart and MOFGA’s planting calendar when talking about planting/harvesting dates; depending on what greenhouse you have or wind up with, you can start experimenting a month or two later than usual for the fall crops and the same amount early for spring crops. It will depend on your greenhouse specifics, but you can generally expand your growing season for common garden fruits and vegetables by 1-3 months on each end, growing later and starting earlier than you would in an outside garden. You’ll have to experiment a bit with your own greenhouse and measure temperatures over a season to really see what is possible; some people are able to grow year-round. You will definitely want a thermometer inside.