Answer: The answer to your question would really depend on what you are trying to grow. For instance, most annuals will not tolerate cool temperatures and the seeds need a soil temperature near 70 or higher to germinate. Greenhouses actually tend to gain heat during sunny days and need to be vented, then need heat on cold nights.
Usually, too, healthy plants are not necessarily going to have pests or diseases right off the bat -- but if you look at your plants daily you will notice anything unusual (little bugs on the growth tips or flying about, holes in foliage, discoloration, or similar changes or "symptoms").
You might find the following extension articles interesting:
Hobby Greenhouses at
and Greenhouse Information Page at
I hope this helps you get started!
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