I had a chance to tour Shadow Brook Farm Friday, southwest of Lincoln, Nebraska. Here, Kevin and Charuth [shuh-Ruth] grow organic vegetables and raise chickens for eggs for their exceptionally long CSA (Community Supported Agriculture) season and raise goats for their milk. Charuth is a talented cheese maker, which is how I met her, but it is their vegetables I went to see. More specifically, it is the work they have done around season extension, adding 8 to 10 weeks on either side of their growing season.
A lot of farmer’s relish their winter as time “off” (there’s always stuff to do- time off on a farm actually means “time with a comparatively short-ish to do list”), but Charuth and Kevin take January and then crank back up. Standing in the high tunnel this morning, when the outside air was perhaps as warm as the upper 30°s F (3° C), the long rows of lettuces and mustard greens glistened with vigor. No wonder- it was at least 15°s warmer (8° C) in there.
High Tunnels, Low Tunnels, Hoops Houses
At Shadow Brook, “in there” means inside a 200’ (61.5 m) long passive solar high tunnel. The passive part is important to them. Charuth grew up The Netherlands, where season extension often means the whole carbon-heavy nine yards of not just heat, but artificial lighting too.
Not so here. While there is a high tunnel (a.k.a. ‘hoop house’) outfitted to operate as a greenhouse, in general this farming family uses heavy grade poly plastic over hollow metal tubes, the classic high tunnel, to extend their season. They are also set up for a low tunnel inside their high tunnel, allowing double coverage overnight to slow the loss of heat built during the day in the soil.
Which crops make good winter vegetables?
Charuth is clear on one of the prime principles of season extension: it’s not that things grow in the winter, it’s that they are willing to not die. This means farmers have to ‘bank’ their crops. If somebody wants a head of cabbage (a very cold hardy family) each week through 12 weeks of serious winter, then all 12 of those heads need to be in good shape and a good size before winter sets in. It’s less about growing and more about staying and that requires some cold tolerance, some willingness to shrug off a freeze.
But even that capacity for flexibility in temperatures had its limits. While the soil stays above freezing, the plants are not guaranteed to do that. Being up in the air, they are more vulnerable to freezing, and that can burst the cell walls, leading to damaged spots on the crops. While romaine lettuce, for example, will put up with a lot of temperature abuse (as will a lot of lettuce varieties), eventually the stress accumulates. The isolated freeze damage becomes less isolated until the day comes when it’s time to call it quits.
In the same vein, the variety of crops that can be grown in the winter is limited: in addition to the low temperatures, there’s the shortened day length, ergo anything that requires blooming is out. So although the pea vines themselves might grow (and they are happier as a spring crop), there will certainly be no peas. On the up side: pea greens turn out to be a tasty addition to most quick meals.
Also known as pea shoots, pea greens sauté quickly, reducing in volume drastically and tasting like you’d expect: peas. If you are going to add onions or garlic, start them first and then add the shoots. Finish with a spritz of lemon if you’re feeling fancy, and then enjoy. One word of warning: pea greens don’t keep. if you get your hands on some, eat’em up in the next day or two.
High Tunnel Design Details
Size and Shape
But back to the high tunnels: 200’ is a very long high tunnel. Usually, they are 48’ or 96’ (~14m or 29m, respectively), a length that allows the air to circulate more easily, in no small part because the longer the high tunnel, the harder it is to roll up the sidewalls for cross breezes during the day. Shadow Brook’s new experiment is a high house with a flat side walls (versus the ground to ground curve of a Quonset hut style pure hoop). In this house, they are planning to rig the walls to, instead of rolling up, lower down from the hip board that marks the top of the side wall.
This is a generally discouraged practice because the plastic then spends the summer laying on the ground, collecting water and mud and generally breeding (literally) trouble. That’s if you lower the plastic all the way. A lot of what makes plant stems tough, and what takes up a fair amount of their energy, is the wind, specifically resisting the wind. By not lowering the plastic completely, they create a very tall faux-baseboard that blocks the wind. They’ll introduce a sizeable gap at the top of the sidewall, and the hope is that that’ll provide sufficient ventilation.
Again, we come back to the wind (I’m noticing it’s always the wind out here on the plains). Will the partially dropped sidewalls act as sails, catching every gust and gale? Or will the plan work? It’s like a suspense novel- the only way to really find out is read to the end of next summer’s tornado season and see how the walls fared. I appreciate their ingenuity, their willingness to try new things. It’s the only attitude that’s ever really worked.
I picked up some other design details for hoop houses at Shadow Brook Farm, too. The first thing to catch my eye as I came down the hill from the on-farm market building was the metal frame of a hoop house entirely devoid of plastic. The stems of perennial cut flowers stood bereft of life, clearly capitulating to the impending winter now that they lacked a roof.
Apparently, when a windstorm came through this fall and tore the plastic from that one house (the others were all fine), Charuth and Kevin decided it was nature’s way of suggesting that this house was ready to stand open for a season. Because high tunnels prevent rains from getting in, the houses must be irrigated. Drip irrigation is both the most efficient and the most popular, but drip irrigation never produces enough water at once to flush any accumulating salts deeper into the soil.
Salts are natural in the soil, especially around here (one of the main streams is Salt Creek), but they tend to accumulate in irrigated settings. Huge swaths of agriculture in western Russia, large chunks of California’s agricultural acreage, and numerous other spots around the world are showing signs of ‘irrigation fatigue’: too much salt too high in the soil layers. In Shadow Brook’s climate, a simple season of rest will solve the issue. Open to the rains and snow all winter, the soil in the open high tunnel will be flushed clean.
The doors were the next thing to catch my eye- not surprising, as the end walls of the high tunnels are the next obvious thing to appear. Several are sliders, which hang from a solid track and reminded me of my horse barn days. The door slips open on the outside of the building, guided by the occasional peg in the ground. The system works, with the somewhat rare episode of ice that somehow worked its way up into the track and needs to be whacked back out.
The door on the hinges was the one that surprised me. It opens out. I’ve seen other farms do this, but usually the door jamb has a floor board high enough to keep the door above shallow snows (less than 8 inches, 20 cm) whereas this one was flush with the ground. The detail that made it more workable: a small concrete pad at the base of the door, which made shoveling the snow much easier and kept a mud pit from appearing in snow shovel induced divots in the dirt.
The high tunnels aren’t the only place crops are grown at Shadow Brook, and I’ll come back and tell you more about what they are up to soon. The design details I’ve given here on the high tunnels aren’t exhaustive either. That’s another future post (with drawings and diagrams and photos, oh my!)