Cover crops can protect against soil erosion, weeds

When gardeners ask me what is the average date of the first killing frost, I have to ask them where they live, exactly. In places near the Hudson River, such as Kingston or Catskill, where many of you reside, the first hard frost may not occur until mid- to late October. Sometimes, it does not happen until mid-November.

At elevations above 1,500 feet, the usual date is closer to mid or late September. By the way, a “hard frost” is the same as a “killing frost.” Frost itself, just refers to temperatures of 32 degrees, which is the temperature that water freezes at. Most of our garden plants can tolerate this temperature for many hours.

It generally requires temperatures in the mid-20s to kill tender garden crops such as squash, beans, tomatoes, eggplant and basil. Cool-season crops such as lettuce, beets, leeks, Swiss chard, cabbage and all its relatives can tolerate much lower temperatures for long periods of time. If frost is predicted for only one or two nights, you can protect your tender crops by draping cloth blankets or sheets over them overnight. Plastic tarps or drop cloths are not nearly as effective.

Typically, temperatures will return to more “normal” levels for days or even weeks

after the first few frosty nights. This period of nice weather after a killing frost is referred to as “Indian Summer.”

A hard frost does kill many insects such as mosquitoes but, unfortunately, not ticks. Some mosquitoes will also survive and can reproduce quite nicely during Indian Summer. Some, but not all, garden pests are also killed by frost.

Most of our ornamentals also vary greatly in their frost tolerance. Some of our annual bedding plants such as petunias and snapdragons are quite tolerant of frost, while others, such as zinnias, are more sensitive. When in doubt, get out the blankets!

This is a good time to plant cover crops in places in the garden that are no longer growing vegetables to harvest. Cover crops protect soil from eroding and prevent weeds from taking over while providing an excellent source of organic matter for the soil. They may be annual plants such as oats or perennial plants such as clover, alfalfa, vetch or winter rye. Legumes, such as clover, vetch or alfalfa are also capable of fixing nitrogen in the soil, which will help to nourish crops in subsequent growing seasons.

The bigger your garden is, the more important it is to plant cover crops, but even small gardens can benefit from additional organic matter and weed prevention. Some leguminous cover crops, such as clover and alfalfa, require more than a few weeks to become established and even longer before they can add any significant quantities of nitrogen to your soil. If you have a section of garden that can remain fallow for a year, they are excellent choices, but if you plan to plant crops the following spring, you should opt for non-legumes.

Winter rye, not ryegrass, is an excellent choice because it can be planted in mid-October and will still produce prodigious quantities of organic matter by the following May. The only downside to winter rye is that it will form a pretty solid sod that usually requires mechanical tillage to incorporate it in the springtime. Indeed, this grasslike cereal grain will grow to three feet tall by mid-May in most areas. You may have to cut it down before tilling it under. That is why farmers often harvest a good hay crop before tilling it in. Winter rye also seems to suppress many weeds by producing an allelopathic chemical that prevents some weed seeds from germinating.

My favorite cover crop is oats. Oats germinate even with cool soil and cool air temperatures. They also grow very quickly, producing a large quantity of biomass in a relatively short time. I also think they are pretty cool to look at! They are frost-sensitive, however, and are killed by a hard frost. They are best planted in mid-August through mid-September.

They are also very easy to incorporate into the soil the following spring and do not require mechanical tillage.

If you have bare spots in your garden now where your summer squash, beans, cucumbers, salad greens or other crops have expired, it would be a good idea to till the soil and plant some oats or other cover crop. This will save you some time next spring when you are busy with other chores!