Broccoli should be harvested when the largest individual flower buds are about the size of a kitchen match head. (Photo by Dan Gill, LSU AgCenter)

Harvest cauliflower when the curds of the head are relatively smooth, much like you see in the supermarket. (Photo by Dan Gill, LSU AgCenter)

Mustard is one of the leafy crops along with spinach, Swiss chard, leaf lettuce, collards and turnips that should be harvested frequently by breaking off the lowest, largest leaves. (Photo by Dan Gill, LSU AgCenter)

For Release On 11/13/15

By Dan Gill
LSU AgCenter Horticulturist

The vegetables we grow in Louisiana during the cool season are some of the most delicious and nutritious that our home gardens can produce. Many of the vegetables we planted in late summer and early fall are now ready to harvest – or will be soon. It is important to harvest vegetables at the proper stage for best results, so here are a few guidelines for some common cool-season crops.

Root crops are harvested when the root is the proper size. Usually, the top of the root is readily visible at ground level, but it is easy enough to brush aside the soil at the base of the leaves to check on the size of the root. Harvest radishes and carrots when the root is about 1 inch across. Carrots can be left in the ground once they are mature and harvested as needed, and the tops can be used as a parsley substitute. Turnips should be harvested when they are 2 to 3 inches in diameter, and rutabagas (a close relative) when they are 4 or 5 inches in diameter. Beets are best harvested at 2 to 3 inches and parsnips at 1 1/2 to 2 inches.

Incidentally, to get good production these plants must be spaced properly in the garden. When the seeds that you plant come up, it is very important to thin the seedlings at least as far apart as the width of the mature root in order to get good production. Leaving the seedlings too crowded is a common reason for root crops to produce small or misshapen roots.

Broccoli heads are not harvested based on the size of the head, but when the largest individual flower buds are about the size of a kitchen match head. Do not allow the heads to remain on the plant so long that some of the buds to open to produce a yellow flower. Remember that smaller side heads will develop after the main head has been harvested, so leave the plant in place for additional harvest.

Harvesting cauliflower also depends more on the appearance of the head rather than its size. The curds of the head should be relatively smooth, very much like the cauliflower that you buy in the supermarket. If allowed to stay on the plant too long, the head will begin to separate and lose quality. If you did not blanch your cauliflower by covering the head with the plant’s leaves, it may have a purple, green or yellow tint to it. This does not greatly affect the quality of the head.

Leafy crops such as mustard, spinach, Swiss chard, leaf lettuce, collards and turnips should be harvested frequently by breaking off the lowest, largest leaves (this is called cropping). Harvest the entire head of semi-heading varieties of lettuce such as bibb, buttercrunch and romaine when the head is fully developed.

Cabbage is ready to harvest when the head is solid and hard. Cabbage is one of the few crops that may be left in the garden after they are ready to harvest, although the heads may split. If you are going to leave fully formed heads in the garden, rotate the entire plant one-half turn to prevent splitting (this slows water uptake by breaking some of the roots).

Snow peas and edible podded peas are productive, delicious and well worth growing. Harvest snow peas when the pods are full size but still quite flat. Edible podded peas, such as sugar snap peas, should be harvested when the pods are full and round but before the peas inside the pod have fully developed. Both types of peas should be checked daily and harvested frequently.

Bunching onions and green shallots can be harvested anytime during the winter when the tops are large enough. Dig up the entire clump and separate off one half of the bunch, and then replant the rest to continue to grow and divide for future harvesting.

Cold protection for winter vegetables

Although winter vegetables are generally hardy, new plantings may need to be protected from hard freezes as will certain vegetables near or at harvest stage. If temperatures below 30 degrees are predicted, young seedlings should receive special attention by completely covering them with a 4-to-6-inch layer of loose mulch like leaves or pine straw. The mulch may remain over the plants for a few days, but remove it as soon as the freezing episode is over. Other protections include plastic coverings supported to keep them off the plants, fabric sheets or floating row coverings may also be used.

Although the plant itself is quite hardy, the heads of broccoli and cauliflower are prone to cold injury if temperatures below 30 degrees occur. The leaves, flowers and pods of peas may also be damaged by hard freezes. Rather than trying to provide protection, the gardener should consider harvesting all mature and nearly mature produce before the freeze.

The following lists will give you a quick guide to the ability of some vegetables to endure freezes.

Protect or harvest if temperatures are predicted to go below 30 degrees: fava beans, broccoli, cauliflower, lettuce, peas.

Will tolerate temperatures down to the mid-20s with little or no damage: Swiss chard, Chinese cabbage, kohlrabi, mustard, spinach, radishes, turnips (although the leaves of radishes and turnips are moderately hardy, their roots are very hardy).

Will survive temperatures in the low 20s and even the teens, especially if given some protection: beets, Brussels sprouts, carrots, celery, collards, garlic, onions, parsley, leeks, shallots.

Rick Bogren