Hooping it Up

Hoophouse at Fertile Fields Farm, Westmoreland, NH
Hoophouse at Fertile Fields Farm, Westmoreland, NH

Written By

Lisa Holderness

Written on

September 01 , 2011

For much of the summer, the sun rises too early for even early birds to see it. But you probably noticed the nights arriving earlier when August rolled around. Perhaps you walked outside at dusk and felt the absence of the swallows. By the time this article hits the stands in September, you’ve probably had your first light frost(s). Maybe even a killing frost, although with climate change it’s all less predictable now.

For a home gardener, this means the end of basil-and-tomato nirvana and fresh food independence. For a farmer, it’s a cash-flow fiasco. But with a little knowledge and some simple tools, we can make the most of that waning sun and feed ourselves a little farther into the fall. We can push our final harvests from the real date of the pilgrim’s first harvest feast in early October much closer to our late-November Thanksgiving Day.

Our first season extension feat at Deer Ridge Farm in Guilford was accomplished on a Thursday afternoon about 10 years ago, with the weather radio blaring a freeze warning. Our tomato vines were still weighted with luscious fruit, heritage raspberries were full of color, and row after row of 5-foot- tall dahlias were in full bloom. Picture us biped mammals, my husband and I, scurrying around with scraps of greenhouse plastic, shreds of Remay row cover, and lots of admonitions. It was the dahlias that were the most challenging, as their flowers and growing tips couldn’t be allowed to touch the plastic or row cover or they would die.

When the adrenaline subsided, reflection and innovation kicked back in. Why don’t we use the same hoop-and-plastic structures we start the season with to round out the other side of the year?

I picked up 10- to 12-foot lengths of PVC pipe to arc over the plants and cut rebar into 8- to 10-inch lengths with a hack saw to push into the ground as posts. I used old greenhouse plastic from our 24-foot x14-foot seedling greenhouse and picked up some extra builders’ plastic. As the temperature plummeted, we pounded the rebar into the soil, slid the PVC over it, bent it into a hoop and anchored the other end with another piece of rebar. Over this makeshift mini-hoophouse, we stretched our covers and anchored them with cordwood and rocks. We covered double rows of tomatoes as night settled in and time and materials ran out.

We spent very little, lost very little, and enjoyed another month of glorious “Indian Summer” markets. Warm days, cool nights, happy eaters, and reassured farmers. I was a convert! Soon we installed our first unheated hoophouse over soil for growing under cover with only solar heat. By then I knew to use IR (infrared reflecting) greenhouse plastic, and I added a second layer, using a small inflation fan to create an insulating pillow of air. Each of those steps added almost 10 degrees of protection, and we experimented for the first year with a variety of flowers and green vegetables.

Last year we added a 30-foot x 72-foot high-side Ledgewood single-layer plastic hoophouse, which lets in the maximum amount of light in spring and fall and has a better surface-to-volume ratio. On cold fall nights, we stretch a breathable row cover over the crops inside it, creating a temporary double layer. On extremely cold nights we stretch a second layer of IR plastic over them. Last November my science students from Kindle Farm High School were able to pick Seascape strawberries, the taste of summer sparkling in their smiling mouths.

Since our original work, I’ve watched the documentary “Blue Vinyl” multiple times with my science classes and I’m turned off by PVC for non-medical uses. So last year I invested in a pipe bender template from Johnny’s Seeds and bought half-inch EMT (that metal conduit electricians use). Ten foot lengths of EMT can be bent into 4-foot or 6-foot wide hoops, with far greater rigidity than the PVC hoops. They are easier to anchor in the soil and less prone to bending under unexpected snow load. We opted for the 4-foot wide EMT so we could get better height for our plants and also greater air volume. Metal conduit can also be purchased in greater diameter or set up with a purlin running parallel to the hoops, lashed or clamped onto the top, to greatly increase structural integrity.

Either hoop will hold plastic over plants. You then need to grab the tails at the ends of rows and anchor them. They can be balled, tied, and anchored with rebar or tree stakes, or anchored all along the sides, as we do with rocks and cordwood—but leave a “flange” when you calculate your plastic width; 12–13 foot wide leaves wiggle room over a 10 foot pipe for a good anchor on each side after you push poles into the ground. You don’t want wind to get up under the edge and rip it off. A third kind of anchor is plastic clamps. These are made of melted segments of PVC pipe. You can figure out how to make them or you can buy them from Pinetree Seeds in Maine or Johnny’s.

Just don’t forget to open the plastic on bright clear fall days, to vent humidity and to give plants a little more solar access. Your mini-hoophouse can overheat very quickly, although its plant “headroom” is a big advantage over the window-sash-over-a-box method. There are several nifty methods for venting.

Enjoy the challenges and benefits of stretching out your season. Initially, you can get more tomatoes to ripen on the vine and pick green beans much later. When fruiting is done, you’ll still have growing lettuce, spinach, and kale. The last benefit will be over-wintering spinach. Give it a little hay insulation and an extra layer over it under your hoop. Then just raise up the coverings and steal some spinach every once in a while. As soon as February rolls around the spinach will start growing like mad again. And it will grow more and more through March and April—just pinch individual leaves and it will “cut and come again.”

Of all the connections I share in my farm life, the biggest gift I can imagine giving my students and guests is solar awareness and a few easy ways to live longer and happier off the land each year.

Photo courtesy of Fertile Fields Farm

Season Extension in a Nutshell

  1. Use PVC, EMT, or local wood to build hoops over your plants.
  2. A purlin/ridgepole gives strength and helps support plastic sheets. Anchor it well.
  3. Use real greenhouse plastic with UV inhibitors and IR (infrared radiation resistance).
  4. Bigger volume = better plant protection from cold and overheating. Tall = good.
  5. Go for maximum light transmission during the day and heat storage at night.
  6. Venting is essential—what saves at night kills in light.
  7. Track your effectiveness with an indoor-outdoor thermometer, just for fun.
  8. Learn the cold-tolerant plants; read Four Season Harvest by Elliot Coleman.
  9. Know the location of the sun in your sky throughout the year. It can change significantly.
  10. Cold air drains downhill. Experiment with this; we plant our peaches and berries on north-facing hillsides. Practice feeling the air and watching for warm and cold spots in your growing area.

About the Author

Lisa Holderness

Lisa Holderness

Lisa Holderness has an MS in environmental science from Antioch New England. She has been a science teacher and environmental educator for 25 years and an organic farmer for 14 years.

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