Growing Fruit Under Cover
by Lynn Byczynski
Protecting Your Investment
High tunnels have spread quickly, and they've clearly proven profitable for vegetables. University researchers have also been studying small fruits in high tunnels and, unsurprisingly, finding plenty of advantages.
For berry growers, protected culture keeps leaves and fruit dry so they're less prone to disease; keeps out birds, rabbits and other berry-loving wildlife; makes weed control easier; shields crops from hail, wind and pounding rain; yields cleaner fruit; and makes picking more pleasant. Many studies found much higher yields under tunnels than in the field, and the longer season let growers sell out-of-season fruit at better prices.
If that sounds appealing, read on. Below we summarize key research, point to useful resources and help you decide whether fruit might earn a place in your crop plan.
Raspberries & Blackberries in Protected Culture
Brambles rank among the fruits most often grown under cover. In California, a leading raspberry-producing state, most of the crop is grown under plastic, on thousands of acres according to USDA estimates.
In the Northeast, field-grown local raspberries usually run from mid-June into early October. A typical outdoor planting of everbearing raspberries might be picked for about 5 weeks before the first hard frost, but under a tunnel covered with plastic in late summer, picking can stretch to 10 weeks or more. Growing both summer-fruiting floricane varieties and fall-fruiting primocane varieties, some under tunnels and some outside, can supply raspberries from May into November. Early and late berries bring better prices, and being first to market can win customers who keep buying all season.
Cornell University specialists report that primocane raspberries grown in a high tunnel for a single fall crop (cut down after fruiting or in early spring) commonly yield several times more than field plantings. They credit less gray mold, a longer harvest, tighter spacing in the tunnel "and possibly other reasons." For full details, see the manual (updated 2012) High Tunnel Raspberries and Blackberries.
In trials in southwest Michigan comparing four summer-bearing and four fall-bearing cultivars, tunnel yields were more than double field yields, and tunnel berries were noticeably larger. The top summer-bearing varieties ('Encore' and 'Nova') bore nothing in the planting year, as expected for biennial canes, a modest crop in year two and heavy crops in years three and four. The top fall-fruiting cultivars produced a fair crop the first year and heavy crops the following two years, and the researchers' economic analysis found the fall-bearing tunnel system especially profitable. For more, see Economics of High Tunnel Raspberry Production.
Pennsylvania research on newer thornless blackberries showed very high marketable yields under tunnels, welcome news since winter injury has long limited field blackberry production there. Breeding has also produced varieties such as 'Prime-Ark Freedom' from the University of Arkansas, which flowers and fruits on first-year canes and bears large, early, flavorful berries. More on the economics and growing advantages is in Small Fruit Production in High Tunnels.
Strawberries in Protected Culture
Unlike brambles, which occupy the ground year-round, tunnel strawberries can be grown as an annual crop. Plugs go in during early fall (September in much of North America) and fruit the next spring. When production tapers off, the plants come out and the tunnel can be used for a summer crop.
University of Missouri research on the annual system found that harvest began about a month before field berries and lasted roughly two months, and a far higher share of tunnel berries were marketable than field berries. The berries also sold at strong prices, and the economic analysis showed a solid return per 1,000 square feet. See Growing Strawberries in High Tunnels in Missouri for the details.
Strawberry plasticulture is replacing the traditional matted-row system on many farms. Plants are set into black plastic mulch from mid-July through September, protected from cold over winter and harvested the next spring. Winter protection is needed where temperatures drop below about 12°F (-11°C). Hay or straw is the traditional mulch, but many growers now use row covers since they take less labor to put on and take off. Heavier covers, 1.25 oz per square yard or more, are recommended.
Pennsylvania research found plasticulture with short-day or day-neutral cultivars viable in tunnels, but concluded that the main advantage of high tunnels for strawberries may be reliable production rather than higher yields.
Blueberries in Protected Culture
Blueberries under plastic have been studied less, and so far the main benefits are protection from birds and frost. A Florida study, though, pointed to big potential gains for Southern growers. Over two seasons on a commercial highbush farm, temperatures outside dropped to or near freezing dozens of times, but inside the unheated tunnels only a handful of times. Tunnels also sheltered plants from wind and rain, improving flowering and fruit set. Tunnel plants delivered a substantial crop by the end of March, when prices peak, while comparable outdoor plants had no ripe fruit yet.
For more on the Florida work, see High Tunnels Yield Better Blueberries.
Undercover Fruit Production — An Attractive Prospect
Research on growing fruit under cover is still young, but the results are encouraging and growers are confirming them in the field. If the idea appeals to you, look into it more closely, prepare carefully and give it a try. The payoff could be significant.
Founder of Growing for Market magazine
She and her family have grown vegetables and cut flowers in Kansas since the late 1980s, selling through CSAs, farmers' markets, restaurants, grocers and florists.
Her books on market farming include The Flower Farmer and The Hoophouse Handbook.
