Cover your fall vegetable garden? It depends

Richard Bogren, Fontenot, Kathryn

Commercial strawberry growers use row covers over strawberries to keep the blossoms from freezing. One row is not covered to show the plants under the cover. Home gardeners can use a similar procedure to protect their strawberry crop. (Photo by Kiki Fontenot)

News Release Distributed 11/13/13

By Kiki Fontenot
LSU AgCenter horticulturist

BATON ROUGE, La. – November weather in Louisiana can be extremely variable. One day we are wearing flip flops and T-shirts; the next, temperatures are dipping into the 30s.

Avid vegetable gardeners welcome cooler weather because with it come harvests of broccoli, cabbage, cauliflower, kale, spinach, turnips, beets, radishes, carrots and many more cool-season crops.

But what about the weather? Beets, carrots, cauliflower, Swiss chard, Chinese cabbage and lettuce will tolerate light frosts, whereas broccoli, cabbage, Brussels sprouts, collard and mustard greens, peas, radish, spinach, onions and turnip crops will tolerate a hard frost.

The LSU AgCenter does not generally recommend covering these crops during a light freeze or when night temperatures drop into the 30s for only a few hours at a time. But you can follow some good practices to protect your fall vegetable garden.

– Mulch perennial vegetables like asparagus. Any mulch will work, but leaves and pine straw are preferred materials.

– Water plants if a frost or freeze is expected. Drought-stressed plants will not tolerate harsh environmental conditions as well as healthy, well-watered and fertilized plants. Even though it’s cool, plants still require regular irrigation. Don’t saturate soil, but keep it evenly moist.

– Freezing temperatures will affect cauliflower. If you can see the developing head, gather all foliage together and tie it with twine to cover the head. This practice is called blanching and will also prevent developing heads from turning yellow when exposed to direct sunlight. Uncovered heads turn a light lavender color in freezing temperatures.

If a freeze occurs and your fall crops have a thin layer of ice on the leaves, don’t break them off. This will damage the plant, reduce photosynthesis and reduce overall yields. Simply wait for the sun to melt the ice, then water at the base of plants to perk them up.

A few cool-season edibles need more TLC (tender loving care) when the temperatures drop.

Strawberry crops need to be covered when temperatures drop below 32 degrees if the plants have flowers on them. The plants themselves are hardy down to lower temperatures, but the flowers are sensitive. Losing flowers means losing harvests.

To prevent lost flowers, gardeners can cover strawberries with light-colored or white floating row covers known as weather protection cloth. This cloth can be purchased at most local hardware stores and must be anchored to the ground around the plants with sandbags, bricks or other heavy objects. If the cover is not securely attached to the ground, the air temperature around the plant will dip below freezing and cause damage.

If row covers aren’t available, mulch around your strawberry plants with pine straw, which can be raked over the plants to protect flowers. When temperatures warm up, remove the covers or pine straw from the tops of plants. Strawberries can remain covered for a period of time without negatively affecting plant development, but you might notice a slight increase in insects below the covers. Check your plants regularly.

Young citrus trees also need to be protected against freezing temperatures. Temperatures must reach the mid- to low teens before killing these trees, but fruit production will be reduced if temperatures dip into the 20s.

Unlike strawberries, a citrus tree should not have mulch or grass growing around its base. Keep the ground bare. If you only have one tree and you expect many nights of below-freezing temperatures, you can build a greenhouse-like frame around the tree and cover it with a clear plastic. This structure must be opened in the early morning to prevent sunlight from burning foliage under plastic.

An easier approach to frost protection is to cover the graft of the tree – the portion of the trunk that buttresses out – with insulation. If the top of the tree (scion wood) is not killed, it may grow back. Otherwise, the tree can be re-grafted. If the bottom portion (root stock) of the tree is lost, re-grafting is not an option.

Some gardeners build up soil around the base of the tree to cover the graft. This works when the tree is younger and the mound of soil reaches 18-24 inches high and 2 to 3 feet wide. Copper fungicides must first be applied to the base of the tree before mounding soil to prevent rots. Don’t forget to remove the soil mound in early spring.

If you are still nurturing warm-season crops such as eggplant, tomatoes and peppers, a cold snap is sure to take these crops out. Few avid gardeners will cover these crops with hoop houses or row covers to try to extend the season. But I see this as a good time to practice crop rotation. Say goodbye to the warm-season crops and enjoy the bounty of cool-season veggies.

Rick Bogren

11/14/2013 1:12:52 AM
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