Tomato seeds are pretty much indifferent to cold. Ill.: ndgbotanicals.com, clipartlook.com & jewel1067.com, montage: laidbackgardener.com
Question: I don’t understand how tomato seeds can survive the cold winters while I live, down to -15 °F (-25 °C), then come up and produce plants in the spring!
Tomatoes come from northwestern South America, a tropical region. How do tropical seeds survive such cold weather? And it’s the same for eggplants.
Does this mean that the seeds have a greater cold tolerance than the plant does?
Question: Yes, that’s exactly the case.
The secret is that the seeds of most plants go fully dormant and, during deep dormancy, are not bothered by extreme cold. Tomato seeds have even been stored in liquid nitrogen at -321?F (-196?C) and sprouted afterwards.
That’s why seed companies can ship seeds with no special protection even under the worst cold of winter without fear for their survival. (Read Yes, You Can Order Seeds in the Dead of Winter.)
Now, there are some plants whose seeds never go completely dormant. (Clivia seeds, for example.) These seeds won’t tolerate frost and can’t be shipped in cold weather, but they’re exceptions rather than the rule. The majority of seeds, even those of tropical plants, will tolerate freezing without difficulty as long as they are fully dormant.
Seeds Survive, Plants Die
On the other hand, when plants are in full growth, they’re all sensitive to frost to a certain degree. Even a fir tree from the Far North, perfectly capable of tolerating temperatures of -31 °F (-35 °C) in the middle of winter, will suffer severe cold damage if a significant frost occurs while it’s growing. But any cold-hardy plant slowly goes dormant in the fall and its resistance to cold gradually increases as temperatures drop. It eventually reaches a point where it can withstand severe cold, although exactly how much cold depends on its natural degree of hardiness, a factor that varies from one species to another.
On the other hand, nature never taught tomato plants and eggplants to prepare for oncoming frost, so they continue to grow late into the fall, as long as the weather permits. Unlike their seeds, the plants are totally intolerant of freezing and even the slightest touch of frost will damage their tissues if not out and out kill them. But their mature seeds can live on, ready to replace them when spring comes.
So, the next time a comet hits the earth and the resulting years-long impact winter wipes out most of the animal species, many plant seeds will simply wait the cold out and germinate when warmer weather returns.
Ain’t nature wonderful?