The primary reason to use any greenhouse structure, whether movable or not, is to provide crops a protected and controlled microclimate. Crops are either grown on benches, in raised beds, or more commonly, directly in level soil within the greenhouse space. This way all crops, whether salad greens or tomatoes, can be easily re-tilled and re-configured if necessary. A movable greenhouse is not actually a new idea but a ‘rediscovered new idea’ – the first commercial movable greenhouse was built in England at the end of the nineteenth century. It was a very large and expensive glass structure and moved along old railroad tracks so it was not realistic for the average farmer or gardener.
Modern movable high tunnels, such as Rimol’s Rolling Thunder, have the advantage of being moved along a track from one growing area to an adjacent area at a scheduled time to accommodate four-season growing. For example, if the tunnel is protecting a summer crop of tomatoes and winter carrots are in need of protection for the winter months but not during the fall growing season, the carrots can be seeded in the late summer in the adjacent plot while the tomatoes are still producing inside the tunnel, and then only once the tomato crop is finished in late fall, then the tunnel can be moved over the carrot crop to protect it for the winter season.
This system creates a ‘best of both seasons’ scenario and the cold-hardy crops that can be grown and harvested during the winter months are quite varied. Since the most economic and sustainable option is to avoid supplemental heating or use very minimal heating, the crops selected for the winter months are cold-hardy enough to withstand cold winter temperatures but since they are protected from the desiccating effects of the wind and outdoor elements, they remain in a perpetual harvest state during the majority of winter.
These crops include spinach, baby lettuces, Asian greens, European greens, salad mixes, carrots, leeks, radishes, onions, scallions, kale, chard, beets and salad turnips. Depending on your USDA plant hardiness zone and without using supplemental heat, some of these crops such as carrots and spinach perform well through the entire winter months while others such as beets and radishes are best to grow later into the fall or started earlier in the spring. Simply from the double protection of the high tunnel and an inner layer of Remay or Agribon, you will be amazed by how much can be grown and survive the cold of winter.
To provide a quick overview, movable high tunnels have many advantages over a stationary tunnel:
1)Movables maximize square footage growing area by two to three times depending on the number of moves per year.
2)With proper planning, the use of a movable prevents summer crops from being removed prematurely from the high tunnel due to fall/winter crop timing issues.
A grower can avoid planting or seeding crops that are adapted to cool weather growing conditions in a hot summer/fall high tunnel.
3)They mediate potential soil and pest issues by exposing the soil to the cleansing effects of the outdoor elements for a season.
5)They accommodate crop rotation issues more seamlessly.
6)They can be used as a ‘Hoop Coop’ to shelter pastured laying hens during the winter months.
7)Using movables enhances the success of four-season production which ensures fresh product available year-round and a more consistent income available for the farmer and farm employees.
Like anything in agriculture, there are always disadvantages to consider:
1)Movables can cost more per square foot due to additional components needed for movability and structural integrity.
2)The endwall designs need to accommodate the moving process to allow for an easy move, sliding over crops, sufficient ventilation and door access.
3)Further planning and foresight must be considered if installing electricity, heating elements or irrigation.
4)Unless movables are properly and securely anchored, they can potentially be blown away or damaged by extreme wind gusts.
5)The learning curve to successfully plan four-season crop plantings and seeding times is more challenging and it is essential to do your homework and be open to learning through trial and error when starting out.
In my personal experience, I am a big fan of movable tunnels from the success I had using them at my farm, Divide Creek Farm in Colorado. Not only did I appreciate the numerous advantages listed above, but they enhanced my customer outreach and relationship marketing by providing an interesting educational topic to engage in conversation at farmer’s markets, during CSA pick-ups, farm tours and at other farm events.
As small-scale farming becomes more competitive, it is important to have niche crops and strong customer relations to ensure the success and longevity of your business. One of my niche crops was the sweet winter carrots which were only available during the late fall and winter months. For the unique advantage of being able to more easily grow freshly-harvested sweet winter carrots, I would always choose to have at least one movable tunnel. The winter farmers market I attended every Saturday provided countless opportunities to discuss the reason why I had fresh sweet carrots to sell and not storage carrots due to the advantage of the movable tunnel to protect the winter crop.
Most people were amazed after sampling a carrot as they had rarely tasted one that sweet and delicious before and many parents would regale humorous tales of how their children quickly became popular at school with lines of kids clamoring to trade for their carrots. If vegetables taste good, it rarely takes any encouragement to get kids to eat them!
While choosing to add a high tunnel, whether movable or not, involves much consideration, I believe the advantages far outweigh the disadvantages and if smartly planned and executed, it will provide a substantial improvement to your farm or garden. Most importantly, the more farmers, gardeners and customers who are inspired and educated about the advantages of movables, the more expertise and innovation we can develop in high tunnel use and design, and the more effective we will be in moving small-scale farming into the twenty-first century for the benefit of all in agriculture.
Additional in-depth information and resources can be found in Eliot Coleman’s books, Four-Season Harvest and The Winter Harvest Handbook and also at his website www.fourseasonfarm.com. And of course, Rimol Greenhouses can answer many of your questions when considering a Rolling Thunder movable tunnel or a stationary model.