Before plunging into the topic of growing fall vegetables, there are two important and relevant horticultural terms you should understand: warm-season and cool-season vegetables.

A warm-season vegetable completes its life cycle in one growing season. Warm-season vegetables are often transplanted when the soil has been warmed, and in some cases, may also be directly seeded into the soil.

Examples of warm-season vegetables include tomatoes, eggplants, beans, cucumbers, peppers, sweet potatoes, watermelon and summer squash.

A cool-season vegetable needs the cooler temperatures to germinate and set seed. Cool-season vegetables may also be referred to as fall or shoulder vegetables because not only are they some of the first to be planted in the spring but may also be planted later into the season. These fall crops are excellent candidates for use with season extenders and tend to be leafy greens and root crops.

Common cool-season vegetables include Asian greens, asparagus, beets, broccoli, Brussels sprouts, chives, cabbage, carrots, cauliflower, Swiss chard, kale, leeks, lettuce, onions, parsnips, peas, radishes, spinach and turnips.

Cool-season crops may grow in warmer temperatures, but the quality of the produce may suffer from the higher temperatures. A good example of this is the radish left in the soil too long. The radish will become fibrous, spicy and will also bolt. Bolting or “going to seed” is caused by a change in temperature and-or day length.

You may have heard people say that certain vegetables taste sweeter following a light frost. This is called “winter sweetening” and is a phenomenon you often see in vegetables that grow naturally in cold weather.

While the first frost of fall will kill lots of plants, there are many varieties, root crops in particular, that will survive these much colder temperatures. This is because, in part, to their ability to convert starch into sugar.

Over the course of the growing season, these vegetables store up energy in the form of starches. When temperatures start to drop, they convert these starches into sugars, which act as an anti-freezing agent for their cells.

This change doesn’t happen overnight, but as long as you pick your root vegetables sometime after the first frost of autumn, chances are good that they’ll taste a lot sweeter than if you’d picked them in the summer.

Carrots, turnips, rutabagas and beets are all roots that get sweet with frost. Some other vegetables that get sweet in winter are cole crops such as Brussels sprouts, broccoli, kale and most leafy greens.

Some vegetables can remain in the garden. Parsnips and horseradish can be left undug, or stored, in the garden over winter. These vegetables withstand freezing, but alternate freezing and thawing damages them. If you store them in the ground, mulch them lightly at the end of the growing season.

Keep them covered until outdoor temperatures are consistently low. Then remove the mulch to permit thorough freezing. After they have frozen, mulch them again deep enough to keep them frozen.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613.