Define Your Goals
The first thing to do when you begin to plan a greenhouse to supplement your food stores during a potential disaster is to define exactly what you want it to do for you. Will it be a resource that you use regularly as a matter of course - supplementing your diet with fresh vegetables and fruits, year-round or just seasonally? Will it be a means of production focused on crops you can grow in bulk and preserve by canning, freeze drying, or dehydrating? Will it be a space where you can learn new gardening skills using trial and error - testing different varieties, starting seeds, propagating using cuttings, perhaps even grafting trees?
Cold Weather Protection
Aside from production goals, you should consider what most important functions your greenhouse structure will provide. Greenhouses are valued largely because of the protection they provide against cold weather. The basic concept of a greenhouse is to allow sunlight in but prevent the sun’s heat from escaping. This keeps the interior of a greenhouse several degrees higher than the exterior air. If you’re in an area where winter temperatures drop below 40°F, or if you want to produce warm season fruits and vegetables year-round, this is a valuable function that you’ll want to preserve.
Warm Weather Protection and More
In warmer climates, you may not need to worry so much about keeping plants warm, but there are other functions that are distinctly valuable: the enclosed structure of a greenhouse can help maintain higher levels of humidity and protects against drying winds, while also limiting exposure to pests. The framework of a greenhouse can also support shades or screens that help deflect much of the intense afternoon heat that might cause heat stress on your plants.
Severe Weather
If you’re in an area where damaging winds, heavy rains, or sudden temperature changes are common, a sturdy greenhouse can make the difference between losing your entire crop or weathering it with minimal damage. If this is an important consideration, keep the types of weather that threaten in mind as you choose the style and material of your greenhouse. A peaked roof can prevent snow accumulation, while a low profile, rounded structure is more suited to handling strong winds, if it’s anchored to the ground. A high-quality reinforced greenhouse cover is less likely to tear or collapse under the weight of snow than a thin plastic sheet, and while PVC tubing makes an inexpensive, easy-to-construct frame, it will be lightweight and not particularly strong.
Temperature Regulation
Greenhouses may have a primary goal of keeping the interior warm during winter or shaded during summer, but there are finer controls you may need from time to time. Even where you’re using a cold weather greenhouse, summertime heat can be extreme and when exterior temperatures rise into the triple digits, no one wants to be in a space that tops off around 120°F or more (including your plants). If this seems like a possible scenario, integrate some ventilation strategies into your greenhouse design. Rolling up greenhouse walls or ends or adding removable ventilation panels along the roof or gable ends are all effective options, and your choices will help you narrow down which type of frame works best for you.
Protection from Pests
A greenhouse that remains closed all year long will be largely invulnerable to infestations, if you are careful about not accidentally introducing them yourself. Carefully inspect any new plants you’re introducing to the greenhouse. In fact, you could introduce a separate or sealed off quarantine greenhouse (or large cold frame) for new plants to ensure they’re not carrying mites or aphids or any obvious diseases. Other than that, though, an isolated environment is the best way to keep your greenhouse free from disease vectors (as we all learned during the COVID experience).
If you need to ventilate your greenhouse during warm seasons, though, you don’t need to completely give up on the idea of protecting your crops. Screens can be installed over ventilation panels or dropped down behind rolled up greenhouse walls. If you’re using electricity, fans can keep a positive pressure to prevent harmful insects from randomly flying in. Don’t be afraid to get creative.
Form Follows Function
There are quite a variety of greenhouse designs, and each type has strengths and weaknesses that make it more or less suitable to particular situations:
- Cold frames are small, very simple, passive structures that may not be much fancier than an old window placed over a basic 6” high wooden frame. They can also be larger, taller, permanent or movable. Cold frames are typically used to warm the covered area to promote early germination of seeds and protect young sprouts from late frosts. They’re also used to extend the growing season for outdoor crops when nighttime temperatures begin to fall but daytime temperatures are still mild. The concept is to close the cold frame when the temperatures are cool but open the frames so the plants can breathe when temperatures are mild (typically during midday). Cold frames are simple, easy to operate and can be made from almost anything with a translucent covering. They’re typically cheap enough to make in bulk, which means you could reasonably cover a lot of crops in your outdoor fields.
- Hoop houses/high tunnels/Quonset huts are simple semicircular tunnels that are lightweight, easy to ship, and can be assembled without specialized tools or skilled labor. They’re among the cheapest greenhouses to build, but they do have some disadvantages: because of the semicircular arch shape, there’s not much headroom along the very edges of the walls, which limits access and productive growing space. They can be easily built with cheap materials, which is a boon to the budget in the short term but makes a structure that may not be strong enough to handle snow, hail, high winds, or even very heavy rain. Hoop houses have almost no internal framing, so space for irrigation systems, mechanized vents, and hanging plants is virtually nonexistent.
- Gothic arch style roofs are something of a middle ground between gable roof style and hoop style greenhouses. The profile of a gothic arch roof somewhat resembles a cross section of an onion dome, with a semicircle stretched up at the center into a point. This type of roof can be installed over vertical walls, providing more headroom and growing space at the edges. The pointed roof design helps the structure shed snow and ice, allowing it to withstand more extreme winter conditions. The frame of the arched roof is very simple compared to the trusses used in gable roof construction, so it is both lighter, cheaper, and easier to build, though not as much as the hoop house.
Gable roof greenhouses use traditional trusses to support the roof. The trusses run parallel to the short sides of the greenhouse and rest on the walls. The walls require a lot of strength to support the trusses, but overall, this design gives you a strong, stable structure that can easily support hanging plants, curtains, overhead irrigation, and other equipment. A gable style greenhouse offers plenty of practical advantages, despite its higher cost and more complex construction, and it may be the best option for survivalists who plan on relying on their greenhouse for the long term.
