Spring sunshine and snowy temperatures
Wow! We are glad to see the questionable weather moving on. As you can imagine, cold, clear spring nights can be rather nerve wracking for any gardener, but keeping a greenhouse warm throughout those nine hours of darkness is a considerable challenge.
Because none of our greenhouses have a true heating system, we rely on passive measures to retain as much heat as possible. One method we found that helps somewhat is to fill a black rubber bucket (available at Rural King 
) with water and as that warms throughout the day, it will slowly release the heat throughout the night.
We also use a tarp to surround the plants as well as adding flat pieces of styrofoam to create a sort of “box” around the plants. This helps tremendously.
The amazing part of all this is, as much as I hate the up and down swings of the thermometer, the plants need this process too. Granted, some tender annuals need extra protection, but all garden and perennial plants are stronger after coming through a few of these nights.
So as much as I cringe to admit it, even the craziness of spring weather improves the quality of the plants we will be selling and planting in a few weeks.
