by Todd Logan
Alaska has a long and interesting history of agriculture, including a government-sponsored relocation of 200 Midwest farm families in 1935 to establish the Matanuska Valley Colony near present-day Palmer. Today a modest number of commercial agricultural operations are successfully operating around the state. Nonetheless, commercial agriculture, even when combined with subsistence hunting, fishing, and gathering, supplies less than 5 percent of the food consumed by the 720,000 residents of the state.
In recent years home vegetable gardening has seen rapid growth in popularity nationwide. The local foods movement and a growing interest in sustainable and self-sufficient living have at least in part fueled this interest. In the Anchorage area, ornamental and vegetable gardening is popular. Our long summer days are a big plus. Our short growing season and naturally cool air and soil temperatures are our biggest challenges. Anchorage gardeners typically reserve Memorial Day weekend to plant most vegetables outdoors. We enjoy harvests from mid-summer until the hard frosts and first snows of mid-October bring the outdoor gardening season to a close.
At our Anchorage home we have had a successful vegetable garden for several years. Leafy greens such as lettuce, spinach, cabbage, and Swiss chard do well here. Root vegetables such as potatoes, carrots, and turnips also thrive in our long days and cool soils at 61°North. However, if you lust for a good tomato, cucumber, or pepper, regardless of season, you must create more conducive growing conditions or accept the imported fare that spends weeks traveling from farm to market.
In 2011 we decided to build a greenhouse. We had two primary goals. First and foremost, we wanted to grow a broader range of vegetables than what outdoor conditions allow, as well as extend the season for the leafy green vegetables we much enjoy. Secondly, we were interested in creating a sunny warm space where we could relax and enjoy a good book now and again. Our mid-winter days are short – 5 ½ hours from sunrise to sunset, and even our July days, on average, only warm up to 65 degrees. We also set some constraints – primarily that the space had to require only modest energy inputs once built, and if possible, capture heat for greenhouse and other domestic uses. We also envisioned significant application of at least 7 of the 12-permaculture design principles:
- Observe and interact
- Catch and store energy
- Obtain a yield
- Apply self-regulation and accept feedback
- Use and value renewable resources and services
- Integrate rather than segregate
- Use small and slow solutions
We began our research and quickly learned that our goals were somewhat in conflict. A good greenhouse does not make a great sunroom, and a glassed space designed to maximize solar heat gain would not make a comfortable greenhouse or sitting space. We didn’t abandon our goals. We just made some compromises and hoped that we would strike a decent balance.
We chose to create an attached greenhouse – one that shares a wall with our existing home. Benefits of attached greenhouses include reduced construction costs, reduced energy needs for both greenhouse and home, and convenient location. We were fortunate to have a well-situated south wall of our house for this purpose. And the dimensions and configuration of our house prescribed the size of our greenhouse – 9’ x 14’. We selected a local sunroom contractor to design the structure and construct most of it. His knowledge from 3 decades in the sunroom/greenhouse business was most helpful. For example, one’s choice of glazing (the glass) requires a trade-off. Glass that allows undiminished light transmission and optimizes solar heat gain has poor insulation values. Since we planned to heat our greenhouse at least part of the year, the insulation value of the glazing was quite important to us. Contrary to standard sunroom design, we selected glazing that seemed to reasonably balance these three attributes for both the walls and ceiling of our new space (light transmittance = 65%, solar heat-gain coefficient = 0.27, U-Value = 0.25).
Many options exist to warm a greenhouse to extend the growing season and create an environment for growing temperate zone vegetables. One can maximize passive solar heating by adding mass such as dark colored masonry and/or water barrels inside the greenhouse. Potential active solar heating systems include subterranean heat and cooling systems (SHCS) and hydronic heat storage. On the fossil fuel front, we considered simple electric space heaters, a dedicated natural gas heater, and/or expanding our existing home’s natural gas and wood-fired furnace hydronic heating system. We ultimately chose the latter, but incorporated some of the solar heat capture approaches as well. After monitoring a season of greenhouse operation, we will likely incorporate additional solar heat capture.
While deciding how to heat an Alaska greenhouse is of primary concern, we are virtually certain that our greenhouse will actually overheat (exceed 80oF) on sunny summer days. Greenhouse cooling is typically handled by manually opening windows or automated with exhaust fans that simply blow excess heat outdoors. We are loath to discard heat in Alaska, even mid-summer! Two potential approaches to cool the greenhouse and capture the waste heat are (1) blowing the warm greenhouse air into the rest of the house with a fan, and/or (2) removing heat from the greenhouse with an air-to-water heat exchanger. With respect to the latter, the warm water generated might be stored and used for greenhouse heating, home space heating, and/or domestic water heating. As stated above, we will evaluate the potential for integrated heating/cooling methods during our first season of greenhouse operation.
Due to all of these heating and cooling options and unknowns, we sought a greenhouse design that maximized future adaptability. We quickly realized that our choice of greenhouse foundation design would affect many options. The simplest greenhouse floor would be dirt, gravel, stone, or a poured concrete slab. While properly insulated dark colored concrete floors are often used in passive solar designs, we felt this approach would be ineffective in a greenhouse filled with shade-creating growing tables and plants. We decided that allowing for active solar heat capture was important and promising, so we went with a joist-supported wood floor over crawl space supported by 6’ deep concrete footers. Water is a superior medium for heat storage, and insulated tanks for hot water storage are an expensive and
space-consuming component of solar hot water systems. The two crawl space compartments beneath the greenhouse were designed to allow them to be retrofitted later with insulating foam sheeting and a pond liner to make two 1000-gallon hot water storage tanks (see www.builditsolar.com). We reasoned that one 1000-gallon tank might be used to store warm water in conjunction with a greenhouse air-to-water heat exchanger. A second tank might be
dedicated to store high-temperature hot water from dedicated solar thermal panels at some point in the future.
Greenhouse construction began in early October. Contractors got the foundation in just before the ground freezes in this part of the world. We then built the floor ourselves. In early November, the contractor tented the site and built the pony wall and glass structure over a 3-week period. In January and February we finished the inside of the pony wall, installed electrical outlets, hydronic baseboard heat, two hose bibs, and water and freeze-resistant vinyl flooring. We finally had a greenhouse!
With respect to growing things, we had yet another goal – low maintenance. We love to garden, but we also love to get into the backcountry regularly to enjoy the amazing wilderness that this part of the world has to offer. With this in mind, we decided to go with “earth box” design growing tables, which will self-water and feed plants for extended periods. We built and tested several mid-sized earth boxes mid-winter, under LED grow lights, and liked our results. Earth boxes (www.seattleoil.com /Flyers/Earthbox.pdf) have a water reservoir in the bottom, then an air layer for healthy roots. Above that the box holds 8” of growing medium, which is topped with fertilizer bands between planting rows and finally a plastic evaporation barrier. Wicking tubes connect the soil layer to the water reservoir. The soil layer stays both moist and aerated from the water and air layers below.
We built two very large earth boxes to be our primary growing tables.
On March 15 we set the greenhouse thermostat to 50oF and planted cool season greens -– lettuce, spinach, kale, and Swiss chard. Sprouting began on schedule a week later.
We are having an unusually cool March. Nighttime temperatures have been dropping into the single digits, with days warming into the 20s. While we are still heating with our wood furnace, keeping the greenhouse near 50o has not been hard. On several sunny afternoons we’ve seen 70o inside. These are good temperature ranges for leafy greens. Indoors we have started warmth-seeking tomatoes, cucumbers, peppers, and celery. In a few weeks these should be of transplanting size. With our warming spring temperatures we can rationalize pushing the greenhouse thermostat to 65o and see how these do. We’ll share our success, or lack thereof, in a future post. We are quite optimistic that we can make this work, but gardeners know you don’t always get everything right the first time!
While we have attempted to share how permaculture principles shaped some of our thinking on this project, we are in no way claiming that we maximized those principles on this project. With a simple Internet search you can find some great resources on passive solar greenhouse designs, use of recycled/discarded materials in greenhouses, and even how to heat greenhouses with compost and animal manure. We encourage you to take a look at these should you ever decide to build a greenhouse.
Finally, the big picture: We must ask, “Should one be trying to grow temperate zone vegetables in Alaska at all? What’s the energy investment in an Alaska greenhouse-grown tomato or cucumber? How does that energy investment compare with one shipped to Alaska from the Central Valley of California, South Florida, or South America? In the energy scarce future, should Alaskans expect to eat tomatoes at all?” Good questions!
The construction of this greenhouse required large energy inputs, including excavation with a tracked excavator and high tech glass and framing shipped from the East coast. High tech engineering and shipping to high latitudes demands fossil fuels, globalization and a broad base of complexity. Food security can be developed with less technology using hoop houses (here and here) and cold frames. While initial costs of an attached greenhouse are energy intensive, operation and maintenance should be much less demanding. Is a greenhouse an appropriate investment in the face of imminent descent? We think so. Will Alaskans have greenhouses, at least of this design, in the future low-energy world? Maybe, maybe not.