Tomato Plants and Temperature
Most tomatoes are warm season plants and should only be planted after the danger of frost has passed. Tomato temperature tolerance for extreme heat or cold snaps is of extreme importance to the development of blossoms and subsequent fruit set. Blossom drop will occur in the spring if daytime temperatures are warm but night temps drop below 55 F. (13 C.). In the summer when temperatures soar over 90 F. (32 C.) with nights over 76 F. (24 C.); again, the tomato plant will suffer damage to immature fruit or loss of flowers. Additionally, when nights become too warm, the pollen grains of the tomato flower begin to burst, thwarting pollination, hence no fruit set. This is doubly true when the air is saturated with relative humidity. The growing temp for tomato seedlings should be maintained at constant temps of between 58-60 F. (14-16 C.), whether starting in the greenhouse or indoors, and then not transplanted until the last frost has passed.
Cold Hardy Tomatoes
There are specific tomato varietals bred for cold hardiness which will tolerate conditions at or below 55 degrees F. (13 C.). The best choices for colder climates are short to mid-season tomatoes. These tomatoes set fruit not only in cooler temps, but also reach maturity in the shortest number of days; around 52-70 days. One of the most popular is called Early Girl, but there are many different cold hardy varieties to choose from. Some examples of hybrid tomatoes for cool climates are:
Celebrity Golden Nugget Husky Gold Orange Pixie Oregon Spring Siletz
Heirlooms varieties include:
Bush Beefsteak Galina Glacier Gregori’s Altai Grushovka Kimberly Legend Manitoba New Yorker
These are just to name a few. A little research should turn up a dizzying list to choose from.
Heat Tolerant Tomato Varieties
Just as there are those of us who live in cooler climates, there are also those who live where temperature conditions run to the more extreme heat index. There are tomato varieties bred for those conditions as well. Some examples of hybrids which are heat tolerant are:
Bella Rosa Big Beef Florida Fourth of July Grape Heat Wave Homestead Manalucie Mountain Crest Porter Sanibel Solar Fire Spitfire Sunbeam Sun Leaper Sun Chaser Sunmaster Super Fantastic Sweet 100
Heirlooms include:
Arkansas Traveler Costoluto Genovese Green Zebra Quarter Century Sioux Super Sioux
Tomato Frost Protection
Besides planting cold hardy tomato varieties, some tomato frost protection may be provided by using plastic “mulches” or covering which will trap the heat to keep the fruit warm if temps drop below 55 F. (13 C.). Dark plastic coverings will raise the temps by 5-10 degrees while clear warm the tomatoes by up to 20 degrees. This may be just enough to save the tomato crop.
