I’m in love with our attached greenhouse. When we found our off-grid homestead, I’ll admit the greenhouse was one of the main selling points.
Finally, a convenient place for starting all my seedlings for our summer garden! I had no idea that the greenhouse would become such a part of our day-to-day lives, and truly essential for running our homestead.
Benefits of an Attached Greenhouse
The main benefit actually has nothing to do with plants or gardening. It has to do with warmth.
If it’s sunny, it doesn’t matter how cold it is outside, the greenhouse will be cooking. We have a door that leads from the greenhouse into our kitchen, and three full wall height windows that we can open to let the warmth into the house.
Some years, if it’s sunny enough, we can go several weeks mid-winter without running any heat. That’s January…in Vermont…with no added heat.
Beyond physical warmth, there’s also the psychological benefit. When it’s -20 outside, and has been for seemingly forever, there’s nothing better than stepping “outside” into a 90-degree greenhouse in a tank top to enjoy a cup of tea.
The way our greenhouse is built, it’s more of an extra room than a simple greenhouse, which really expands the options in our 1 room cabin style home.
Starting Seeds in an Attached Greenhouse
While I assumed that the greenhouse would be the perfect place to start my seedlings, it’s actually not as great as you might think. Many seeds need to be started indoors in late winter to get a headstart on our very short Vermont growing season. That means starting some seeds as early as February.
It’s true, the greenhouse is warm on sunny days, but it doesn’t keep the constant warm temperatures that seeds need to germinate. Cold isn’t the only problem.
When the sun does come out, the greenhouse can rapidly heat to 100 degrees or more if you’re not watching, even if it’s below zero outside. With the cold outside temps, all the vents are closed so it could be dangerous for fragile seedlings.
Heavy winter snows can also cover the glass and block out sunlight, and even without snow, the days are remarkably short in late winter.
Pests are also a huge problem. Since the temperatures stayed relatively warm over the winter, and heat up quickly in the spring, pests are quick to come out of hibernation and attack tender seedlings. Aphids have been a particular problem, and they’ll destroy or stunt seedlings.
With all those considerations in mind, we do some of our earliest seed starting inside the house. For tender seeds, it’s best to think of the attached greenhouse as one giant cold frame. The greenhouse can be used to grow out seedlings and help harden them off before planting, but we don’t count on it for seed starting.
Paved Floor or Dirt Floor Greenhouse
I love the idea of planting right in the dirt, but practically speaking I’m glad our greenhouse has a floor. Managing extra soil moisture against our basement could turn into a nightmare, not to mention a disruption in the freeze/thaw cycle of the ground right against the foundation.
Having a real floor in the greenhouse also makes it seem more like a living space.
Greenhouse Moisture Issues & Drainage
Whether you have a paved floor or a dirt floor, drainage will be an issue. Ours has a drain in the floor at one end that shunts water about 100 feet away from the house into a runoff ditch.
As far as the siding of your house goes, I’d still consider the inside of the greenhouse to be an “outdoor” space and you should weatherproof your house accordingly. Ours has a vapor barrier under cedar V-groove planking that gives it a bit of an interior look, but much of the resilience of an exterior finish.
Be sure to use flashing to keep any water running down the side of your house from infiltrating the attachment point at the top of the greenhouse. Our greenhouse uses a rubberized barrier that slips up under the cedar siding above the greenhouse and flaps over the top edge of the greenhouse to allow any water to just keep flowing down the outside.
Roof Angles & Snow Load
Since our greenhouse has a significant slope, snow load isn’t as much of an issue as you might think. We take a large push broom out and sweep it off, which allows sunlight to warm the glass. That warmth melts any last remaining bits of snow off and helps keep the attached solar panels free of snow.
The main issue is ice. The roof above the greenhouse has an icebreaker bar to break up falling roof ice as it comes down to help protect the greenhouse.
We haven’t had any issues yet with broken glass or panels, even with substantial ice. It is a bit terrifying when the ice does fall through. Such a crash, and there’s a part of me that always worries.
Incorporating Solar Panels into an Attached Greenhouse
The solar panels at the top of our greenhouse just make sense. In the winter months, the sun angle is lower and most of the light directly impacts the glass. The solar panels don’t shade the greenhouse at all.
In the summer, when the sun is higher in our northern latitude, the solar panels shade the greenhouse and the windows on the side of the house, which keeps everything nice and cool even in the heat of the day.
The greenhouse environment under the panels also means that the solar panels melt out quickly after snowstorms. We have other solar panels attached to our shop/garage and they’re very high up on a steep roof.
When we have an ice storm, there’s no way to clear those panels and they can remain useless for weeks at a time. That’s not the case with our greenhouse panels, which provide a much more reliable source of off-grid electricity.
Summer Heat Considerations
A greenhouse is designed to trap heat, and when the days are long and warm, too much heat can be a problem. Our greenhouse has a door on each end that we leave open all summer long.
In the late spring, we open the two full-length vents, one at the top of the greenhouse and the other along the south side. Those vents are operated by antique hand-crank mechanisms, which means we’re not dependent on electricity for venting.
Manual venting has its benefits off-grid since you’re not dependent on power or computers. It also has downsides. We have to plan ahead if we’re leaving the house and vent the greenhouse if we think it might be sunny later. It doesn’t take more than 20 minutes or so of direct summer sun to bring temperatures up to dangerous levels for the plants in a fully closed greenhouse.
There are many times I wish we had an automated vent attached to a temperature sensor. In an ideal situation, install something automated, but have manual backups.
Greenhouse Pest Problems
Continuously warm temperatures mean that once pests take hold, they can really rage out of hand. While ladybugs go to bed for the winter, aphids will keep right on going if temperatures are favorable and they have a food source.
We originally grew winter greens such as arugula, claytonia and tatsoi in the greenhouse to supply our family all winter long. It was great until warmer temperatures in March arrived.
The aphids woke up and devastated the greens. We tried just about every organic control on the books, but the greens were still painted with aphids and eventually died.
We’ve since changed our plan.
The only year-round crops we grow in the greenhouse are herbs, which have their own defenses. We never have pest problems on rosemary, oregano, tulsi and thyme.
Beyond pests that impact the plants, we also have pests that impact our house. Wasps are a significant problem.
They love the warm environment and it’s a constant battle to keep them from building nests in the eves inside the greenhouse. We hang a non-toxic sight lure wasp trap and we have to change it out monthly in warm weather because it becomes so covered in wasps.
The biggest problem is keeping the wasps out of the house when we’re trying to use the greenhouse to heat the house in the spring. Be sure to install good screens on any windows that lead to the greenhouse, because pest pressure is actually higher inside the greenhouse as compared to the rest of the outdoors.