Before you decide on a greenhouse kit or plan, there are three things you want to consider. What is the purpose of your greenhouse, how big do you want it to be, and where will you put it? Answering the first question will help you in answering the other two.
What do you want to use your greenhouse for?
There are three main purposes for a greenhouse. The first is to grow things in the winter, or at least extend your season past when you could grow outside. The second is to start seedlings earlier in the Spring, for transplanting outside. The third is to grow Summer vegetables. In the Pacific Northwest you can’t count on a good Summer for tomatoes and peppers, so many people put them in their greenhouses.
For the first two purposes, you want to keep the greenhouse as warm as possible. That means keeping it relatively small and having double paned windows. The double walled polycarbonate works very well. You may also want to consider getting a lean-to greenhouse and putting it against the south side of your house or other building. The building will insulate the greenhouse and protect it from the wind. If you are starting seedlings you want enough space to benches or planting tables. It is much easier to work with your seedlings standing up than crouching down.
If you are planning to use your greenhouse for Summer vegetables, you’ll need to keep it cool. Lots of opening windows are important. You may also want to get a fan to improve circulation. Most tomatoes grow quite tall, so make sure there is enough vertical space above the planting beds.
How big should your greenhouse be?
The short answer is, no bigger than necessary. Unless you are only using it for Summer vegetables, you want to be able to keep the heat in. The more air space there is, the faster the heat dissipates. If you are not growing Summer vegetables, keep your greenhouse as short as is comfortable for you. Think carefully about how much you will use your greenhouse and how many plants you will put in it. Many people wish they had gotten a bigger one after the first year, but you don’t want a lot of empty space.
Where will you put your greenhouse?
The most important thing, of course, is to put it in a very sunny location. The next thing to consider is do you want your greenhouse to be freestanding or up against the south side of your house or other building. Given the choice, against a building is best. Besides conserving heat, it conserves space. You also don’t have to worry about shading other parts of your garden. Shading the garden is the last consideration in planning the location. Look at your site carefully. If you have not started a garden already, plan out the space, even if you don’t think you will put a garden in, in the near future.
Having gotten clear on those three issues, you need to decide whether you want to buy a greenhouse kit or build it from plans. That is really a personal matter, and I’ll leave it up to you. Lastly, make sure you have plenty of ventilation. There should be some windows in the roof, so the hot air can go up and out. Automatic window openers are a must on every greenhouse, to avoid accidental overheating. I like doors at both ends of my greenhouse. It really helps keep the air flowing in the Summer.
Now you are ready to start looking at greenhouse kits or plans and choose one that will work for you.
