Emergencies that can trigger food shortages can come in a multitude of forms: pandemics, weather emergencies, regional or global military actions, widespread civil unrest (often due to hunger), or the effects of pollution and resource depletion. It’s hard to decide what circumstances to prepare for. Looking at today’s news alone, we see widespread drought, predictions of “widespread energy emergencies” due to drought and extreme heat resulting in soaring demand, and continued labor and supply chain issues.
Let’s look at some possibilities for establishing an efficient, (relatively) disaster-proof strategy for your garden and greenhouse.
Going Passive
Many greenhouses don’t operate in a perfectly ideal location and owners often choose to augment the building’s natural insulating properties with supplemental heat or cooling, depending on expected extreme winter or summer temperatures. This is well and good for many, but if depending on a reliable supply of affordable energy isn’t part of your strategy, it’s time to consider alternatives. Keep in mind that some of these alternatives need to be built into your plans before construction even starts since they can be difficult (but not impossible) to add later.
The most important role of a greenhouse is to maintain temperatures that support plant survival and even growth and production during the coldest nights of winter. In high latitudes or high altitudes, this may be difficult to achieve. Here are some solutions that rely on easily accessible renewable energy and some others that require some manual work, but none of them depend on electricity, gas, oil, or other purchased resources:
- Geothermal heating/cooling: Temperatures a few feet below ground (below the frost line in very cold regions) are a steady 50°F - 65°F, thanks to Earth’s natural heat. Inexpensive passive geothermal systems can be installed for effective temperature control pretty much anywhere on the planet, provided there is a deep enough layer of soil. The basic structure of a passive geothermal system involves burying a winding layer of flexible corrugated drainage pipe adjacent to the greenhouse (or even underneath if you’re so inclined). The ends of the pipe should be connected to outlet and intake vents at opposite ends of the greenhouse. When nighttime temperatures begin to fall, cooling the interior of the greenhouse, the natural tendency of air to maintain temperature equilibrium (2nd law of thermodynamics) will pull colder air from the greenhouse into the pipes and push out air that’s been naturally warmed underground where the pipes are buried. Note that this same concept can be used to cool greenhouses during summertime, but it may not be as efficient.
- Sunken Greenhouses: Another way to provide additional (free) insulation and take advantage of geothermal properties is to partially bury your greenhouse. This works best in regions where the average winter temperature doesn’t dip below freezing, typically from the south eastern and south central US across and up along the west coast. Sink your greenhouse several feet in the ground and that portion will not be exposed to chilly winds and freezing nighttime air temperatures. This will block out some sun exposure, so it may be worthwhile to build tables or raised beds and devote the underneath parts for tool and material storage.
- Thermal Storage/Natural Batteries: Since greenhouse temperatures rise in the daytime when the sun is shining, it’s possible to take advantage of certain materials’ tendency to absorb and retain heat. The cheapest, easiest, and most popular types of thermal batteries used in all sorts of greenhouses are large black plastic barrels filled with water. Water has excellent properties for thermal storage, it’s cheap and easy to install, and it’s completely passive. Consider the layout of your greenhouse and select locations where you can place a series of barrels where they receive plenty of sunlight (remember your plants need sunlight too) and are distributed fairly evenly throughout the growing areas. No pipes or fans are necessary - the laws of physics alone keep this system operating. This type of passive system will work will in relatively moderate temperatures where the temperatures rarely dip below freezing, but if that’s a risk or you’re wanting to grow tender vegetables and tropical plants, a secondary system like geothermal is a good option.
- Insulation: Many greenhouses are designed to have gaps along the roofline for summertime ventilation, but this allows significant heat to escape during the winter. Unless you’re using kerosene, natural gas, or wood to provide supplemental heat, you don’t need to worry about venting out carbon monoxide or other dangerous gasses and it’s a good idea to seal those up carefully. During hot weather, you can open doors and any mechanical vents you’ve installed along the eaves to promote air circulation as well as keeping your geothermal circulation going. Your choice of greenhouse cover will also greatly affect your insulation factor. A double walled cover, like energy-efficient double-paned glass, takes advantage of the insulating factor of dead air trapped between the layers, making it highly efficient. You can construct your own double walled system but purchasing panels or double walled flexible sheets require much less work and are easier to repair.
- Blankets and thermal covers: If you’re in a region with occasional or intermittent cold snaps, you can keep your plants thriving with a low tech, not-so-passive but effective practice. Essentially, you can tuck your greenhouse in at night and keep it cozy through the coldest weather by manually placing insulated covers over your greenhouse walls and roof (if possible). Thermal blankets & quilts, foil insulation blankets, or even fiberglass roofing sheets are possibilities. Make sure you’ve set a system of grommets and hooks to make installation quick and easy, and don’t forget to remove the blankets when the sun rises in the morning!
Fertilizer
As your plants grow and produce - whether it’s leafy greens or yummy tubers, nutrients in the soil are depleted unless they are returned in some fashion. Commonly, hobbyists and commercial growers alike turn to cheap and easy to use chemical fertilizers. Remember those bags of general “garden plant food” marked with the numbers like 10-10-10? The material inside is typically grayish and crumbly and it’s toxic if you inhale or swallow it. You can choose to use chemical fertilizers, of course, and bagged fertilizer has no expiration date if it’s kept dry and unopened. Right now, however, these tried-and-true gardening staples are in increasingly short supply since the major producers of both potash and finished fertilizer are Ukraine and Russia.
If you’d prefer to use a more natural, sustainable fertilizer that’s not so dependent on international trade, you have a few options. You can make your own using materials like epsom salt, eggshells, fish tank water, and kitchen compost. Establishing a kitchen compost pile is a great idea in any event since composted material improves the condition of your soil, improves its ability to retain moisture, and supports colonies of beneficial organisms. Worm farming is another great idea and may be entertaining for your kids.
