October 24, 2013

Lettuce in January: Winter Growing at the Aquaponics Project

Laura Genello

Laura Genello

Guest Blogger

Johns Hopkins Center for a Livable Future

aquaponics-bok-choyWelcome 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.




  1. Posted by Sarah Parks

    You wrote a very interesting article Laura ! I’m a mother of 2 little boys, so I’m home with the two little devils 🙂 My hobby became the gardening and I started to grow some vegetables by aquaponics. I found a very nice guide how to set up a whole aquaponics system here: http://easydiyhome.com/
    You should check it if you are also interested in urban agriculture.

    Bye 🙂

  2. Laura Genello

    Posted by Laura Genello

    Glad you enjoyed the post, Sarah. We run open hours at the CLF Aquaponics Project every Wednesday from 10am – noon, if you ever want to come see our system. Stay tuned for more aquaponics blog posts soon.

  3. Posted by Rusty Connors

    Dear Laura,
    I live in buffalo NY and would like to do aquaponics
    but our winters can be pretty cold and windy.
    I like the hoop style greenhouse.do you live in colder climate?
    Are the costs for electric and propane high for the winter months.
    I would like to see if this is going to work,I enjoy gardening and like hope
    This works.
    Thanks Rusty C

  4. Laura Genello

    Posted by Laura Genello

    Hi Rusty,

    We’re located in Baltimore, MD. It gets pretty chilly in the winter, but certainly not as cold as Buffalo. We heat the water in the fish tanks with electricity, and the air in the greenhouse with propane. Energy use is our largest expense besides labor. In Buffalo, you may also be concerned about snow loads and the ability of a hoophouse to withstand the weight. I would recommend contacting farmers in your area who grow in greenhouses or hoophouses, even if they don’t practice aquaponics. Winter growing is gaining popularity nationwide, and some of these growers may be willing to share energy-use numbers that would be relevant to your region. Good luck, and keep us posted if you do start an aquaponics system.



  5. Posted by Brian Beun

    I’m looking to start up a farm in Western North Carolina and doing something very similar to what you all are doing. What size tanks are you using and what size is your hoop greenhouse and is it single or double layer?
    What type of floor does your greenhouse have?

    Keep up the great work,


  6. Laura Genello

    Posted by Laura Genello

    Hi Brian,

    Our fish tanks are 200 gallons. The hoophouse is 1250 square feet and it is double layer plastic. The floor of the hoophouse is landscape fabric and gravel. If you have other questions, feel free to email me at lgenello@jhsph.edu



  7. wow, great reading
    I’ve been wondering about this for quite some time
    I live in tropical part of the world, but this question still intrigues me
    Gonna do more researches along the way

    thank you Miss Laura

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