High Tunnels

Spring 2013

Speakers at MOFGA’s November 2012 Farmer to Farmer Conference addressed three crops suitable for growing in high tunnels: raspberries, ginger and winter sprouting broccoli.

Raspberries in High Tunnels – Prospects for Maine

David Handley of UMaine Cooperative Extension said that raspberries are challenging to grow, especially regarding labor. They’re the one crop he deals with that has the largest number of people getting into – and out of.

Handley explained the life cycles of summer-bearing and everbearing raspberries.

Summer-bearing raspberries have a two-year life cycle. The top part of the plant – the cane, the green shoot that comes up from underground – emerges the first year, when it’s called a primocane. Over summer and into fall, axillary buds form in the leaf axils of primocanes. As winter approaches, those canes turn brown and the buds become dormant.

In the second spring, that brown cane is called a floricane, and buds that formed in the leaf axils break dormancy and become shoots called fruiting laterals. Fruit is picked from those laterals in summer. When harvest is complete, floricanes die.

In everbearing brambles, canes also live for two years. They produce a primocane the first year, with axillary buds that produce fruiting laterals the second year, but they also produce fruit on the topmost buds in the fall of the first year.

Tunnels give earlier production of both types and later fall production of everbearing types. Tunnels also keep water off plants, reducing disease problems – possibly a greater benefit than increased production, said Handley, especially in an organic system.

Site preparation involves making beds 16 to 24 inches wide and 6 to 10 inches high for drainage. Trickle irrigation can be buried or placed on the soil surface, where it’s easier to maintain – but mice may chew it less if it’s buried, and it’s easier to accidentally prune equipment on the surface when pruning brambles.

Ground cloth can control weeds between rows; leave a channel open where canes can emerge.

Before planting, adjust soil pH to 6.0 to 6.5 and add recommended amendments. If using compost, note that its pH can be high; at Highmoor Farm it was 7.2. Fertilizer doesn’t need to be high in the first year. A slow-release nitrogen (N) source providing100 pounds per acre of N can be worked into the soil before planting. Once plants start fruiting, they need more fertility.

Plant Types

Tissue cultured plugs come in plug trays and are usually dormant. They have less chance of carrying disease; are easy to handle; produce uniform, vigorous growth; but they cost two to three times more than regular, dormant canes; are frost and drought sensitive; and are available in fewer varieties.

Dormant short canes are primocanes that came up in the spring, went through the summer, went dormant in fall, and then nurseries dug them and usually cut them to about 1 foot high. These are typically used outdoors, planted about 2 feet apart in rows; they also work fine in high tunnels. Once planted, buds on the crown areas start to break that spring, providing new shoots to establish that row. Dormant short canes exhibit variable growth but are less expensive than plugs. They begin to produce the year after they’re transplanted.

Dormant long canes usually have to be special-ordered. The are like short canes except that they produce a small summer crop for some early financial return. They are more expensive than short canes and are planted about 1 foot apart in rows, so twice as many plants are needed. These are used in Europe to grow raspberries as an annual crop – which is probably not economical here.


Primocane-fruiting (everbearing) varieties of red raspberries are typically grown in high tunnels, because they produce a big fall crop and can produce a summer crop.

The most common, early varieties are, in order of ripening, ‘Polana,’ which is very productive, ‘Autumn Britten,’ popular for its fruit quality, although it’s a little smaller than ‘Polana’ and does not taste so good, ‘Caroline,’ which is highly productive and has very good fruit quality but is a very aggressive plant, requiring attention to pruning, and ‘Heritage,’ an old favorite with small fruits by today’s standards, but with tasty fruits. In the field, ‘Heritage’ starts to ripen in the last week of August or first week of September. It’s at least two weeks earlier in a tunnel.

‘Josephine’, later than the above varieties, is also the largest fruiting of these.

Some new varieties that look promising include, for very early crops, ‘Joan J’, which has nice fruit but is in the same season as ‘Polana’ and does not have quite the yield of ‘Polana.’

‘Polka’ is a few days later than ‘Polana’ and has better fruit quality.

‘Himbo Top’ is late; like ‘Josephine’, it has very good fruit quality, but the very tall canes have some winter issues.


Plant as early as possible in spring – or even in late winter, if tunnels are up. Raspberries don’t mind cold soil, so plant them as soon as you can work the soil – except tissue cultured plugs: Their growing tips can be very sensitive to cold temperatures, so have row covers ready for these if a freeze is expected, even if they’re in a high tunnel.

Space long cane plants 1 foot apart and short canes 1 to 2 feet apart in rows, with rows a minimum of 6 to 8 feet apart. Leave at least 3 feet between the side of the tunnel and the first row.

Plants can be grown in pots that are moved in and out of tunnels, freeing the tunnel for other spring and early summer crops. Grow plants in 3- to 7-gallon pots (or start them in 3-gallon pots and move them to 7-gallon pots in the second year) – pots large enough to support three to five canes – in well-drained media with a pH of 5.5 to 6.5 and with sand or gravel in the bottom of the pot for weight. Plant one plug or dormant cane per pot. Top the media with compost or sawdust to retain moisture and inhibit weeds. Roots should be air-pruned as they grow out holes in the bottom of pots. If roots start circling the inside of the pot, remove the plant from the pot, score the roots with a sharp knife, and return the plant to the pot.

Move potted plants into the tunnel when they flower (the second season in most cases) and keep them there through fruiting and harvest. Provide adequate space and a trellis for each pot. The earlier they’re put in the tunnel, the earlier the crop will be, but if an early crop is not your goal, you can bring them into the tunnel later (mid- to late summer). Tunnels, including caterpillar tunnels, can also be erected over plants in the field.

Trickle irrigate at least once per week in early spring and late fall and three times per week during summer, for about two hours each time, with a standard line that runs about 0.45 gallons per100 feet per minute. Once plants have a fruit load, their demands for water are fairly high. Invest in a tensiometer for about $30 to test soil moisture.

Overwinter potted plants outside – cut them back, stack them close together and cover them with straw mulch, or bury pots in sawdust in a cool building. Canes should produce well in pots for three to five years.


After taking a soil test and applying recommended nutrients, no supplemental fertilizer should be needed in the planting year – unless you’re trying to get a crop in the first year; then you may need a little extra nitrogen, calcium and magnesium.

Tissue test mature promocane leaves yearly toward the end of summer and adjust fertilizer amounts based on results.

If plants look lush and green, nutrition is probably good. Yellowing between veins can indicate nitrogen, sulfur or iron deficiency, or spider mites.


Trellis plants so that they don’t flop over and are easy to get into. Trellising systems in high tunnels are usually much narrower than in the field. A simple hedgerow, with plants held in place with string strung from post to post, or a narrow V trellis works well.


Raspberries grow best under cool conditions; try to keep the temperature between 70 and 80 F. At higher temperatures, heat stress can damage flowers (and heat stress can be compounded by oil-containing Pyganic sprays). Roll up sides in the morning, close them at night, or keep them open on hot nights.

In fall, keep sides down on cold days, especially on cloudy days, to keep temperatures between 60 and 70. Strong wind can lower yields, while gentle breezes displace stagnant air, which otherwise supports disease development. Fans can help move air around.


Raspberries don’t require cross pollination; they will pollinate themselves if a lot of air is moving through the tunnel – which isn’t always the case. So open sides and end doors to let bees and wasps access flowers. Supplemental pollination with bumblebees early and late in the season may also be necessary.


For primocane types, soft tipping is popular – breaking the growing point (the top 3 to 4 inches) off in June when new canes are 30 inches tall to manage cane height. Tipping can also stimulate more and earlier lateral branching lower on canes, increasing yields and causing more uniform ripening.

Tipping can delay harvest two to three weeks, because it stimulates vegetative growth lower on the cane at the expense of fruiting shoots at the tip of the cane. Also, the harvest can be staggered by pinching. If you have three or four rows, you can allow one row to come up, unpinched, to produce the first crop; the second row can be soft pinched, delaying harvest a bit. Pinching twice would be pushing the limit in Maine unless you have a very early variety.

After harvest, pots can be taken out of the hoophouse. Cut canes at pot level, or, for plants in the ground, mow them down in the fall or early spring before they bud out – unless you want a summer crop from everbearers. One grower mows one row and lets the other row stand in order to get a small summer crop and a fall crop. In a high tunnel, because the season starts early and is extended, and because primocanes are coming in earlier, the summer crop and fall crop can overlap, which won’t happen in the field. That can be a management problem, as you try to cut summer-fruiting canes out to enable primocanes to develop. When summer cropping in a tunnel, have only three to five canes per linear foot, and keep rows narrower than the top of the bed.


Raspberries are highly perishable. Harvest them when they’re cool and dry – first thing in the morning, after the dew dries.

Pick into shallow containers. Half pints are standard, with fruit no more than four-deep so that bottom fruit aren’t crushed.

If raspberries must be held, refrigerate them immediately, as close to 32 F as possible and with air moving through them.

Harvest regularly: three times per week in summer, twice per week in fall. A raspberry is ripe when it separates easily from the receptacle but before the fruit color darkens.

Labor is often an issue, and people generally don’t like to do pick-your-own with raspberries, said Handley. Pickers have to be careful to pick only ripe berries, not to pinch or bruise them as they pick. Also, the crop is ready when a lot of other farm work is going on.

Extending the Harvest

A high tunnel alone will extend the harvest by a couple of weeks. In a good year, by growing both summer fruiting and primocane types, a July through November harvest is possible. Soft-pinching the primocanes also gives another two to three weeks – and can stagger the harvest of any particular cultivar. Growing early, mid and late-season varieties also staggers the harvest. Using row covers on fall nights will add a few degrees of protection and keep fruit producing a little longer.


Tunnels greatly reduce disease pressure, as plants and fruit stay drier, which inhibits development of grey mold (but powdery mildew loves high tunnel conditions). Keep plant density a little narrower and ventilate tunnels well to encourage air movement. Oxidate helps control powdery mildew well.

Two-spotted spider mites do well in tunnels, causing lower leaves to turn yellow or bronze, weakening plants, and, in high enough populations, moving to fruits – which customers won’t like, and which can reduce shelf-life of fruits. Mites are visible with a hand lens. To control them, release mite predators early – they are very effective in high tunnels. Asked about spraying water to control them, Handley said water with a mild soap solution applied about twice per week, with about six total applications, will work, but be sure plants dry within an hour to limit disease problems.

Aphids carry viruses. Their damage shows up as puckering. Eliminate alternate hosts growing near tunnels, such as wild brambles. Pick off leaves, rogue plants showing symptoms, or use several sprays of soapy water, being sure to get good coverage.

Japanese beetle populations are reduced in high tunnels. If they do appear, hand-pick them early in the morning, before they’re too active.

The spotted wing drosophila, a small fruit fly, is a new pest from Asia that lays eggs on ripening fruit. Raspberries are its favorite fruit here, and it thrives in the humid conditions along coasts.

Populations explode around the second to third week in August, so later-fruiting varieties are most susceptible. Damage can approach 100 percent.

“We had people walking away from their raspberry plantings this year because they could not keep this thing in check,” said Handley. The larvae destroy the shelf-life of fruits; a single fruit can have 30 maggots in it.

The only control available now is regular, frequent spraying as soon as fruit starts to ripen. Entrust does a very good job, but its label does not allow for frequent applications. Pyrethrum is not the best control material, but alternating it with Entrust will reduce the buildup of resistance. “If you spray Entrust three times a week,” said Handley, “you’ll run off label quickly, and the insect will start building resistance.”

Adding 2 pounds of sugar in 100 gallons of water with the pesticide gives much better control of the insect, he added; when sensors on the fly’s feet touch the sugar, the insect’s tongue goes down and hits the pesticide. More than 2 pounds of sugar, however, encourages molds on plants.

Fine screening (not regular window screening but the finest ProtekNet, for example) can exclude this pest, but you have to block every opening – and then watch the greenhouse temperature, because the fine screening reduces air movement. One participant said that an NRCS grant can help pay for Proteknet, which costs about $600 for a 5-foot-wide roll. Fedco carries it.

Don’t let fruit fall on the ground, said Handley; and put fruit in the refrigerator as soon as it’s in the home so that eggs won’t hatch. (Eggs seem to need temperatures of 50 F or above to hatch.)

Some native parasitic wasps are attacking pupae and adults. Handley did not know if they give enough control to suppress the pest.

Better traps and baits for traps could lead to a trap-out strategy – i.e., surrounding fields with traps to prevent flies from entering fields.

Blueberries are the drosophila’s second favorite fruit. Burning blueberry fields may help a little, but people are moving away from burning and spraying, Handley noted.

Control weeds before planting. Landscape fabric, plastic mulch, mowing turf or cultivating can control weeds between rows. Keep weeds away from sides of tunnels, too, so that they don’t blow seeds into the tunnels.

Advantages and Disadvantages

Growing raspberries in high tunnels produces larger fruit, yields two to three times those in fields, and provides better shelf life because fruits never get wet. Raspberries are in high demand at local markets, restaurants and schools, and the long harvest season can mesh with some off-season prices. So the profit potential is very good if labor costs can be controlled.

However, the crop requires a relatively high initial investment, and labor for picking a pint can be $0.50 to $1.50 or more – and harvest occurs when kids are back in school. Additional labor is required for handling, grading, delivery and marketing. Raspberries have slightly lower per-acre value than tomatoes and cut flowers.

Bottom Line

Cornell University shows a 10-year cash flow net of $42,889 (excluding marketing costs) for a 30- x 90-foot tunnel. (www.fruit.cornell.edu/berry/production/pdfs/hightunnelsrasp2012.pdf)


High Tunnel Raspberries and Blackberries, Cornell University, Department of Horticulture Publication No. 47 (2012 rev), by Cathy Heidenreich et al. www.fruit.cornell.edu/berry/production/pdfs/hightunnelsrasp2012.pdf

Raspberry and Blackberry Production Guide for the Northeast, Midwest, and Eastern Canada, 2008, NRAES-35, https://host31.spidergraphics.com/nra/doc/Fair-Use-Web-PDFs/NRAES-35_Web.pdf. Handley says this publication is a little out of date regarding varieties.

Ginger seed pieces from East Branch Ginger. Photo by Polly Shyka.

Fresh Ginger

Ginger Dermott and Daniel Price of Freedom Farm in Freedom, Maine, talked about growing ginger (Zingiber officinale) in a hoophouse. Freedom Farm raises 15 acres of mixed vegetables and a small beef herd.

Dermott and Price grew ginger in a 17- by 44-foot hoophouse in 2011 and, in 2012, doubled the production space. They got about 11 pounds of product for each pound of planting stock in 2012.

They order disease-free, certified organic planting stock for about $9 per pound from East Branch Ginger in Pittsboro, N.C. (www.eastbranchginger.com), which represents Puna Organics in Hawaii (www.hawaiianorganicginger.com). Puna ships stock to growers; it arrives around March 1. In 2011 they grew the Big Kahuna variety, which takes a lot longer to “wake up,” and in 2012, Ruhi, which wakes up sooner.

Ginger is grown somewhat like potatoes, said Dermott and Price. They greensprout mature, cured ginger root (actually rhizomes) for six weeks in their walk-in cooler, heated to 75 to 85 F with a space heater. They put about an inch of half Living Acres NP mix combined with half peat into lily crates; the mix is not too heavy or wet. The planting stock is set in the crates tightly, on top of the soil mix, and then covered lightly with a little more soil and peat mix so that a little skin of the stock is showing. They mist the crates about once per week and keep them in the dark. When green sprouts emerge, standard incandescent lights in the cooler are turned on.

When “a lot of green” appears, they move stock to a propane-heated seedling house. It grows slowly there initially because of the 65 F nights. Once the soil temperature in the Inflation Buster hoophouse reaches 55 to 60 (around June 1), they transplant stock there, where, “once it takes off, it really takes off,” said the growers. With soil temperatures over 90 for extended times, the crop rots in the ground, so Northern growers have an advantage over Southern.

Freedom Farm’s ginger at the Common Ground Fair. English photo.

They planted about 35 pounds of rootstock in each 17 x 44 house. The recommended planting rate is 30 pounds per 100 linear feet, but they planted about 40 pounds per about 200 feet.

Their stock was planted in six rows, 5 inches apart within rows, with rows 3 feet apart. They cut a furrow about 4 inches deep, transplanted the stock, and filled the furrow until the ground was level.

They initially fertilized with fishmeal, then switched to a product by Organicare called PURE, a 1-5-4 material with 6 percent calcium. Ginger is a heavy feeder, they said. Treat it like alliums, giving it less fertilizer more often. Every time they hill (every two weeks), they add a little fertility.

They hill by rototilling the paths and hoeing the loosened soil, making sure no pink roots are exposed. Hills are ultimately about 8 to 12 inches high, and plants reach about 4 feet in height.

The first year they buried drip irrigation, but that wasn’t washing fertilizer into the hill well, so they switched to an overhead sprinkler the second year. They emphasize that the soil should not be too wet.

Ginger has few pests. They suggest rotating out of the house every couple of years.

They harvested from early September 2012, through September, and sold about 400 pounds just at the Common Ground Fair. They need to grow more to meet the demand.

One 800-square-foot house took about 32 pounds of stock and produced 343 pounds of ginger, sold at $15 per pound and grossing more than $5,000 (more than $6 per square foot). The crop takes just a couple of hours per week of labor to hill and fertilize.

Harvest involves loosening the soil on the edge of the hill, digging the roots (they grow down about the depth of a fork and don’t grow outward that much) soon before market, clipping the tops, cleaning up the roots coming off the bottom, snapping the roots into half-pound sizes and putting them in clear plastic bags. Other farmers are selling fresh ginger by the ounce for about $1.25 to $1.50. Their Portland Farmers’ Market customers were very excited about the crop and didn’t flinch at the price. They bring a display piece with tops still attached. They sold to restaurants for the same price. They sell tops for $2 per bunch for juice and tea.

They are producing ginger for fresh use, not for storage, because Maine doesn’t have a long enough growing season for the latter. Fresh ginger is less fibrous and thinner-skinned than storage ginger. “It’s like cutting a stick of butter,” they said. “You don’t have to peel it.”

Fresh ginger can be used right away, kept for about a week in the refrigerator, or frozen raw. “Pull it out frozen, grate as much as you’re going to use, and put it back in the freezer,” said the growers. One person tried drying the crop but it didn’t do well. Storage ginger might be possible if plants were brought indoors to develop thick skins, but they don’t transplant well.

Traditionally fresh ginger is pickled in rice wine vinegar. It’s also candied and is “incredible for juicing,” said Ginger. Since the mother root does not produce well when replanted, Ginger suggested clipping it off and using it in lactofermented products or ginger beer.

East Branch’s website has recipes.

Marcia Ferry said Peacemeal Farm sold its fresh ginger for $12 per pound. They sold out at the farmers’ market right away, and a lot of customers froze their ginger.

Winter Sprouting Broccoli

Becky Sideman of the University of New Hampshire Cooperative Extension talked about producing winter sprouting broccoli, a crop she encountered in early March 2003 at a farmers’ market in England. This is Brassica oleracea, like the regular broccoli we grow in summer, but it is grown under a different time schedule – e.g., planted in August or September, overwintered and then harvested as early as February and up to April in England. Also, instead of a single head, it produces many small shoots.

“The flavor of sprouting broccoli in spring is phenomenal,” said Sideman. Purple and white varieties exist. Newer hybrids can be planted in spring or fall.

Sideman and a coworker trialed winter sprouting broccoli because from September through April it might fill tunnels used for summer tomatoes. They trialed 10 varieties started on different dates, from August 1 to September 15, in high tunnels in Durham, N.H. (zone 5b), with and without black plastic, and with different types of row covers. The crop is grown outdoors in England in areas that correspond to our zone 8a to 9a, with an average minimum winter temperature of 14 to 23 F.

Early varieties tested were ‘Red Spear’, ‘Bordeaux’, ‘Santee’; midseason were ‘White Sprouting Early’, ‘Burbank’, ‘Colusa’, ‘Red Head’, ‘Red Arrow’; and late were ‘Ninestar’ and ‘Claret’. Many of these are unavailable or very difficult to find now, said Sideman. ‘Santee’, ‘Burbank’ and ‘Colusa’ are hybrids but many older varieties are not, so saving seed and selecting from them is possible, if their seed can be located.

Three-week-old transplants were set in staggered double rows in 30-inch-wide raised beds, with 9 inches between each plant within rows and 3 feet between row centers. The first year, the ground was fertilized with compost and manure before planting to receive approximately 50 pounds of N per acre. The second year, a slow-release organic fertilizer was used.

Plants in tunnels, with row covers, have survived when minimum outdoor temperatures were -19 F, in tunnels, -5 F, and under tunnels plus row covers, +5 F. Plants in tunnels were covered with heavy (1.25-ounce) spunbonded polyester row cover from late November to early March. One grower heated a house to about 35 F and his crop looked great, said Sideman.

“I am quite certain the plants will not survive our winters unprotected,” said Sideman. “I also found that they did not survive when protected only by low tunnels (e.g. Johnny’s Quick Hoops with heavy rowcover plus plastic).”

Harvest the entire long shoot – leaves, sprouts and all – from March 20 to mid-May, said Sideman. “The whole thing is very tender and delicious.” Most varieties were harvested over three to five weeks, but ‘Santee’ – the most readily available variety and the most uniform – was harvested for only a couple of weeks.

Typical yields were 5 to 8 ounces per plant. Sideman says yields up to 10 ounces per plant may be possible with closer spacing and “a cushier environment.” If you can keep a house around or above freezing, yields should be higher, said Sideman. She also thinks wide beds with plants spaced about 6 inches apart would increase yields. White varieties yield more but are not as attractive as purple, so might be harder to sell.

No significant differences in mean total yield occurred when transplants were set in mid- or late September or mid-October.

Sideman says that she tries to get plants in the ground by late September, although “the jury is still out on the best transplanting date.”

Marketing is easy. Sideman gave samples to chefs, who were ecstatic. They were able to use sprouting broccoli for anything for which they would use asparagus or broccoli. Sales techniques could include using a catchy name, such as asparagus broccoli, selling in mixed color bunches and packaging a set amount in bags.

Growers need an early market, such as restaurants , specialty markets or spring CSAs (but they need to get a high price for the crop). Consumers need to be educated to use the whole stalk.

Economically, sprouting broccoli gets tough competition with spinach for an unheated house in winter. In 2008, in a 30- by 60-foot tunnel, Sideman harvested 136 pounds of sprouts from a layout designed for research and not for maximum commercial production. At her spacing of 2.25 square feet per plant, her tunnel could house 800 plants, yielding more than 200 pounds. At Farmer to Farmer, she suggested a minimum price per pound of $5 to $8.

One limitation with this crop is the small number of varieties available – Johnny’s and High Mowing have ‘Santee’, a purple-sprouting variety that does not need vernalization. Other limitations are the relatively long growing season for a short harvest season; moderate yields; and the marketing efforts required.

An aphid explosion one year was controlled with predators, and the insects were confined to older, outer leaves, which aren’t harvested. Sideman warned that growers should consider the possibility of insect pests carrying over to summer crops.

Asked about overwintering regular broccoli, Sideman said some people are overwintering ‘Happy Rich’, a Chinese broccoli cross. ‘Tendergreen’ might survive. In her experiments, ‘DeCicco’ survived but lacked quality in spring.

For more information, see Winter Sprouting Broccoli – A new crop for high tunnels? by Clifton Martin and Becky Sideman at https://extension.unh.edu/Agric/Docs/BroccoliSheet2010.pdf.

– J E

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