Never let your greenhouse drop below this temperature if you want to keep seedlings alive – plus 7 easy ways you can protect young plants against dangerous levels of cold

Pepper seedlings in a greenhouse with a thermometer.

Sowing seeds indoors in late winter can be a great way to start plants earlier in the year. Seedlings can thrive in constantly warm environments when blessed with a heated greenhouse. However, if you have an unheated space, knowing the minimum greenhouse temperature for seedlings, and protecting plants on cold nights, is important.

Seedlings will be safe as long as the minimum greenhouse temperature reads above 45°F. Cold winter nights can regularly see temperatures drop below this safe level and then it pays to protect seedlings in an unheated greenhouse.