The lawn tomato (Solanum lycopersicum) is a tender, heat-loving plant which needs a quite long frost-free season. Gardeners usually extend the tomato season by starting plants inside and putting out well-developed transplants shortly following the normal last frost date. An early autumn frost, however, can bring a premature end to your own tomato plants, so that it makes sense to consider the possible advantages of frost protection.
The Effects of Frost
“Frost” is a common term that’s actually of little use to gardeners. Cold temperatures affect various plants in various ways, and the harshness of plant injury brought on by low temperatures is affected by several factors, such as the duration of the low temperatures, the wind speed along with also the garden’s microclimate. However, tomatoes are quite tender, therefore it is safe to assume that any night with temperatures near or below 32 degrees F will cause substantial damage on your own tomato plants.
Adequate Sunlight
Rumors can theoretically continue to grow and develop fruit with only seven hours of direct sunlight per day, but such a short photoperiod won’t sustain the vigorous development which occurs throughout the long days of summer. As fall days become shorter and your tomato plants slow down, you might discover that frost protection is not worth the effort after a certain date.
Decreasing Temperatures
Frost protection will aid your tomato plants to survive below-freezing temperatures, however, the cool nights of late summer and fall can still inhibit proper pollination and fruit ripening. In case your first few frosts occur relatively early in the season, the coming weeks might offer a lot of heat and sunlight for your tomatoes. In such scenarios, frost protection is a great idea — a small labor and time might reward you with a bountiful prolonged harvest. But when the cold weather has settled, frost protection alone will offer little benefit.
Varieties
All tomato crops are damaged by freezing temperatures, but certain varieties have a better ability to grow and ripen fruit in cool weather. These varieties will provide you the greatest return on the labor and cost associated with protecting your plants from frost. The Oregon State University Extension Service recommends the following varieties (among others) for tolerance to cold weather, particularly cool nights: Stupice, Glacier, Northern Delight, Oregon Spring and Legend.