Answer: This is always a difficult determination to make and may require some experimenting. Some plants such as tomatoes are best protected from temperatures below 40 or even 45 degrees, while others such as snapdragons are more cold tolerant and are fine into the 30's. You might move some of them earlier than others but stand ready to cover them with a garden blanket or row cover should a frost threaten. Should a hard freeze threaten, you might want to move them back in again. It might be a good idea to use a min-max thermometer to check how cold the greenhouse gets compared to the outdoor temperature, as well as to check how hot it gets on a sunny day. The smaller greenhouses tend to have big temperature swings and there is a danger of overheating as well as cold.
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