Answer: Occasionally bulbs are up and then frozen when grown in the soil. Generally this does not harm them. I often have a hard freeze after the bulbs are up and budded or even blooming. So I'm not surprised that they survived and bloomed happily.<br><br>As far as heating the greenhouse: You were forcing the bulbs to bloom earlier than their natural blooming time and needed the heat in order to speed up their blooming. If you'd rather not do that, forget heating the greenhouse and let them flower naturally in the spring. However, I don't think that's your intention.
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