October 24, 2013
Welcome to the Aquaponics Blog Series. We routinely share updates, photos and fun tidbits from the CLF Aquaponics Project. If you’re interested in urban agriculture, sustainable aquaculture, or hydroponics, be sure to check back regularly for new posts.
Many visitors to the CLF Aquaponics Project ask us the same question: “What do you do in the winter?” Because our project is located under a plastic hoophouse, we’re able to do the same thing in January that we do in July: grow food! However, this time of year, we do need to make adjustments to what and how we grow to prepare for colder weather.
All summer long, the sides of our hoophouse are rolled-up to allow air and pollinators to circulate through the greenhouse. In the fall, I start checking the weather compulsively, scanning the forecasts for nighttime low temperatures. Temperatures of 40 degrees Fahrenheit or below can spell danger for frost sensitive plants and prompt us to roll down the sides at night. Once the nighttime temperatures are regularly 40 degrees and below, our hoophouse sides will stay closed day and night, allowing us to retain more heat. We also cover the fish tanks with insulated caps to keep the warm water from evaporating into the cold air.
The greenhouse is heated in two ways. Electric aquarium heaters keep the water at 70 degrees Fahrenheit for our tilapia, a tropical species that needs warm water to grow. We also use propane heaters to keep the air temperatures above 38 degrees to avoid a freeze that could injure our plants. Fortunately, since all of our plants’ roots sit in the warm water, the plants behave as if it’s warmer than it actually is.
The most important way in which we prepare for winter is in our plantings. We remove sensitive summer crops like cucumbers and basil and start planting cold tolerant leafy greens, such as lettuces, kale, and Swiss chard. Despite their delicate appearance, these greens can actually survive a heavy frost. As the days shorten, we try to get all of our winter crops established by mid-November. After daylight savings, our hoophouse only receives about two hours of direct sunlight each day! Light can limit plant growth even more than low temperatures, and we’ve found that seedlings are very slow to grow if started too late in the season. Although the hoophouse we use is not ideally positioned for solar gain, we could not pass up a chance to work with the Department of Recreation and Parks at the Cylburn Arboretum, and we’re thankful for the space.
By following these measures, even in January, we’re able to maintain weekly harvests of fresh vegetables, like romaine lettuce and mustard greens.
Photo: Laura Genello, 2013.