Cover strawberries for winter

Perhaps the last garden chore of the season is tucking in the strawberry planting for winter. Strawberry plants have already set their buds for next spring’s flowers and the crop can be lost unless you protect them from harsh winter conditions. A fully dormant strawberry plant’s flower buds can be damaged at temperatures below 15 deg. F.
In addition to flower bud damage, the alternate freezing and thawing of the soil that commonly occurs in winter and early spring can cause plant roots to break and the plants to be heaved right out of the ground.
Mulching strawberry plants will insulate them from extreme low temperatures, minimize soil heaving and decrease excessive drying (desiccation) of the plant crowns. But be sure to wait until plants are dormant before you pile on the mulch. Applying mulch too early can cause the crown of the plant to rot. Plants should be mulched before the temperature drops below 20 deg. F, usually by late November or early December in most parts of Indiana.
Several materials can be used for winter mulch, including clean (weed-free) straw, chopped cornstalks, hay, corncobs or bark chips. Tree leaves and grass clippings are not recommended, since they tend to mat down and smother the plants. About 2-3 inches of mulch, after settling, should provide adequate protection.
Put a note on your garden calendar to uncover the plants in spring as new growth begins. Rake off most of the mulch as soon as the first new leaves develop. The new growth will probably look a little yellow at first but will green up with exposure to light. Rake the mulch between the rows to provide weed control and a source of emergency cover in case frost threatens. Mulching around the plants will also help keep the berries clean.

Strawberry Plants And Frost: How Do You Protect Strawberry Plants In Cold

Strawberries are one of the first crops to make their appearance in spring. Because they are such early birds, frost damage on strawberries is a very real threat. Strawberry plants and frost are fine when the plant is dormant during the winter, but a sudden spring frost when the plants are blooming can wreak havoc on the berry patch. Protecting strawberry plants from frost is of paramount importance, but HOW do you protect strawberry plants?

Strawberry Plants and Frost

Frost can decimate an entire berry crop, especially if the berries have been exposed to warming temperatures. A freeze following warm spring weather can be devastating. And strawberries are particularly susceptible to frost damage since they are often in bloom before the last frost free date.

Strawberry blossoms are most sensitive to frost right before and during opening. At this juncture, temperatures below 28 F. (-2 C.) will damage the blossoms, so some frost protection of strawberries is integral to the harvest. Frost protection of strawberries is less important when the flowers are still in tight clusters and just barely peaking from the crown; at

this point they will tolerate temps as low as 22 F. (-6 C.).

Once fruit begins to develop, temperatures below 26 F. (-3 C.) may be tolerated for very short periods, but the longer the freeze, the higher risk of injury. So, again, it’s important to be prepared to protect the plants from frost.

How Do You Protect Strawberry Plants from Frost?

Commercial farmers do a couple of things to protect the berries from frost and so can you. To protect them from winter temps, mulch over the strawberries in the fall to early winter with straw or pine needles. In the spring, move the mulch between the plants after the last frost. This will help retain soil moisture, retard weeds, and prevent dirty irrigation water from splashing on the fruit.

Overhead irrigation is another popular method for protecting strawberries plants from frost. It sounds crazy, but it works. Basically, the farmers are encasing their entire field in ice. The temperature of the ice remains at 32 F. (0 C.) because as the water becomes ice it releases heat. Since strawberries aren’t injured until the temperature falls below 28 F. (-2 C.), the berries are saved from frost injury. The water must be constantly applied to the plants, though. Too little water can cause more damage than if no water is applied at all.

Another interesting fact on protecting strawberries from frost is that soil retains heat during the day and is then released at night. Wet, thus dark soil, retains heat better than dry, light colored soil. So a wet bed serves yet another purpose.

Also, row covers can provide some protection. The temperature under a cover may equal that of the air, but this takes a while and may just buy the berries enough time. Water can also be applied directly over the row cover to protect the flowers inside with a layer of ice.

Where your berries are located can also provide them with some protection. Our strawberry patch is on the south side of a garage with a significant overhanging eave, which serves to protect the berries.

Although strawberry plants can be quite cold hardy, they need protection to survive the winter. In North Carolina, growers use floating row covers to protect strawberries in the winter. In Indiana, straw mulch is a more traditional way of winter protection for strawberries grown in a matted row system.

After two relatively mild winters in 2015 and 2016, I heard successful stories about growing strawberries with the plasticulture system and using row covers for winter protection in Southern Indiana. Can the system also be successful in a colder winter, like the one that just passed? Our ongoing strawberry study will provide the answer. This article provides an update from this project comparing strawberries covered with straw mulch (about 4-inch thick) and row covers (two layers of 1.5-oz/yard2 row cover laid on wire hoops) this past winter (Figure 1).

Figure 1. Strawberries were covered with straw mulch and row cover. Picture were taken on Jan. 9 2018.

Temperature

Between Dec. 27 to Jan. 6, we had the coldest nights of the season in Vincennes, IN. The recorded lowest temperature was around -5°F. The lowest temperatures under row covers were 10°F, while under straw mulch, it was about 15°F. At the dormant stage, strawberries are hardy to 10°F. The plants under row covers encountered the threshold temperature thus we lost 3 out of 192 plants and a few plants were injured. Note the difference of plant growth of the same variety under row covers (Figure 2).

Figure 2. Different size of Chandler plants under row covers. Picture was taken on Mar. 27 2018.

Temperature fluctuations were the greatest under row covers. Temperatures under the row covers reached 50°F on sunny days, even when the outside air temperate was quite cold. Temperature fluctuations were the smallest under straw mulch, and ranged from 15°F to 32°F. The accumulated heat under row covers suggests the plants could potentially come out of dormancy early and be subject to cold damage.

Relative Humidity

Relative humidity was the highest under straw mulch, while lowest under row covers. The high relatively humidity explained why the majority of the leaves were rotted when we removed the straw in the spring. The rotted leaves and the remaining straw provide the perfect condition for the development of Botrytis fruit rot. Compared with the strawberry plants covered with straw, the plants under row covers were much cleaner. We removed the dead leaves on these plants, which is a strategy effective in controlling Botrytis.

We will have more updates on the project as the season progresses. Watch for opportunities to see our research at upcoming SWPAC field day on June 13, 2018.

This article was also published on Facts for Fancy Fruit https://fff.hort.purdue.edu/

Row covers gaining popularity in strawberry production

“His words were ‘I want to sleep!’” says Poling.

This grower had relied on overhead sprinkler irrigation for spring frost protection until he started experimenting with row covers in the late-1990s, he says. The all-night watering sessions required for frost protection with overhead irrigation were eliminated with row covers.

Now, the only reason he has to use a sprinkler system might be for evaporative cooling and an occasional late-season windborne freeze during bloom, says Poling.

“A floating row cover of 1.5 ounce-per-square-yard weight can do the same job as overhead sprinkler irrigation for frost protection,” he says.

You can also save a lot of money on the fuel bill for pumping water,” he adds. And by keeping the crop “dry” with covers, it isn’t necessary to spray nearly as often for botrytis during the bloom period.

The distinct disadvantage of overhead irrigation for frost protection is that it uses such a significant volume of water. It also causes erosion in the row middles and ends, and it washes pesticides from the strawberry and leaches fertilizers from the field.

By comparison, strawberry row covers conserve water, reduce soil erosion, and reduce fertilizer leaching. They can also reduce spraying relative to conventional overhead sprinkler irrigation.

There are important limitations to using row covers for certain types of cold protection, especially when temperatures are expected in the low twenties or the teens during bloom.

Sprinkler irrigation has been the accepted practice for frost protection for many decades, says Poling. “If a grower did not have an adequate water supply for overhead sprinkler irrigation system, he or she was advised not to go into strawberry production.”

The water requirement for an overhead sprinkler irrigation system is usually estimated on the basis of three consecutive frost or freeze nights, he says. For example, 5.4 acre-inches of water would be needed for sprinkling at the rate of 0.18 inch per hour for control down to 24 degrees F., for 10 continuous hours each night over three nights. Or 1.8 inch per night for three nights equals 5.4 acre-inches.

“An irrigation pond would need to hold about 150,000 gallons of water for each acre of plasticulture production under these conditions,” says Poling. “That’s a lot of water.”

Exciting development

The fact that small growers have demonstrated row covers can be used for late-season frost and frost/freeze protection without overhead irrigation is a fairly exciting development, says Poling.

“Farmers with relatively limited water supplies can now grow strawberries in the plasticulture system and achieve full crops in most seasons using the covers.”

For more information on strawberry row cover management, go to the North Carolina Strawberry Information Portal at www.ncsu.edu/enterprises/strawberries.

These row covers are known as spunbound or non-woven fabrics, says Victor Lilley, vice-president of Reddick Fumigants, Inc. “They are most commonly made of polypropylene or polyester,” he says. “They are manufactured by melting the appropriate plastic or combination of plastics and spraying fine filaments onto a belt.”

The belt conveys them to a bonding roller that presses and fuses them together where they touch.

Improvements in manufacturing over the last 20 years have made possible the availability of large covers that can be laid directly on plants. “Such covers can improve earliness, yield and quality,” Lilley says. “For plasticulture strawberry growers, the benefits are in the areas of over-wintering protection and late-season frost/freeze protection, and they also promote fall growth of plants in colder climates.”

Row covers give the greatest benefits when they are fitted to one’s individual strawberry production system, he says. “Geographical location, proper management of the covers with regards to application and removal timing and the management and use of covers with overhead irrigation for late-season freezes,” he says.

Strawberry growers in mild climates like the Coastal Plains and Piedmont typically use row covers for late-season frost or freeze protection. Most growers in these regions view row covers as insurance policies: They may not be needed, but are invaluable when they are.

When covers are used for only short periods such as this, their exposure to the elements is greatly reduced, so less expensive lightweight row covers can be utilized. The benefits of lightweight covers (0.5 ounce per yard) for freeze protection can be greatly enhanced if they are used in combination with overhead irrigation.

Growers in colder climates like the mountains should use row covers as part of their strawberry production system and should consider the heavier and better-quality materials due to the length of time these materials will be exposed to the elements.

Some cold-weather growers apply covers as early as December, leaving them on until well into late February, thus extending their exposure to long periods of time.

Temperatures in these areas have been known to dip low enough to cause plant mortality if row covers are not available to protect and shield plant crowns.

For these reasons, medium to heavy covers should be considered, says Lilley. “But they should not be too heavy: Covers that block more than 50 percent of available light can actually slow growth and advancement of one’s strawberry crop.”

Lilley’s company, TriEst Ag Group was recently formed from a merger of Hendrix & Dail Inc. of Greenville, N.C.; Reddick Fumigants LLC of Williamston, N.C., and Hy-Yield Products Inc. of Rocky Point to service southern farmers’ fumigation needs. You can reach the TriEst main office at 800-637-9466.

[email protected]

Although strawberry plants can be quite cold hardy, they need protection to survive the winter. In North Carolina, growers use floating row covers to protect strawberries in the winter. In Indiana, straw mulch is a more traditional way of winter protection for strawberries grown in a matted row system.

After two relatively mild winters in 2015 and 2016, I heard successful stories about growing strawberries with the plasticulture system and using row covers for winter protection in Southern Indiana. Can the system also be successful in a colder winter, like the one that just passed? Our ongoing strawberry study will provide the answer. This article provides an update from this project comparing strawberries covered with straw mulch (about 4-inch thick) and row covers (two layers of 1.5-oz/yard2 row cover laid on wire hoops) this past winter (Figure 1).

Fig. 1 Strawberries were covered with straw mulch and row cover. Picture taken January 9 2018

Temperature
Between Dec. 27 to Jan 6, we had the coldest nights of the season in Vincennes, IN. The recorded lowest temperature was around -5°F. The lowest temperatures under row covers were 10°F, while under straw mulch, it was about 15°F. At the dormant stage, strawberries are hardy to 10°F. The plants under row covers encountered the threshold temperature thus we lost 3 out of 192 plants and a few plants were injured. Note the difference of plant growth of the same variety (Figure 2).

Fig. 2 Different sizes of Chandler plants. Picture was taken March 27 2018

Temperature fluctuations were the greatest under row covers. Temperatures under the row covers reached 50°F on sunny days, even when the air temperate was quite cold. Temperature fluctuations were the smallest under straw mulch, and ranged from 15°F to 32°F. The accumulated heat under row covers suggests the plants could potentially come out of dormancy early and be subject to cold damage.

Temperatures 12/2/17 to 1/6/18

Relative Humidity
Relative humidity was the highest under straw mulch, while lowest under row covers. The high relatively humidity explained why the majority of the leaves were rotted when we removed the straw in the spring. The rotted leaves and the remaining straw provide the perfect condition for the development of Botrytis fruit rot. Compared with the strawberry plants covered with straw, plants under row covers were much cleaner. We removed the dead leaves on these plants, which is a strategy effective in controlling Botrytis.

Relative Humidity 12/2/17 to 1/6/18

We will have more updates on the project as the season progresses. Watch for opportunities to see our research at upcoming SWPAC field days.

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