All greenhouses are “solar” greenhouses–they gather heat from the sun! But, over time, solar greenhouse has come to signify only those structures that are specifically built to collect heat during the day and release heat at night, making supplemental heat unnecessary. Here at the nursery, only one of our six growing structures is a solar house. The smallest greenhouse here, built on the south side of the house, needs no supplemental heat to stay above freezing all winter. It’s amazing what you can grow in it. We use it to start seeds, overwinter tender stock plants, take cuttings in the fall–we even grow food in it. Lettuce and peas–all the cool season crops–do just fine in this greenhouse in the winter. On sunny days it’s so warm it helps to heat the rest of the house. On the coldest nights, when we’re trying to germinate seeds in January and February, we leave the door between the greenhouse and the house open (taking away some of its solar cred.) Surprisingly, strawberry plants produce all winter in this little house,
giving new meaning to the term “everbearing strawberry.” The two above are almost ripe enough to pick. Here’s another picture taken today, a flat of cuttings that I started back in October. 
They’re rooted now and in February when I need the space for starting more seeds, I’ll move them out to a cold frame. By that time they’ll be big enough to get along on their own. Called Bonsai Crassula by some, the scientific name for it is Crassula sarcocaulis var. rupicola. Rupicola means of rocks, and is a specific name for more than one plant that we grow. Like most succulents, this one is easy to grow from cuttings, but we orginally grew it from seeds from the Denver Botanic Gardens. There is a plant there that has survived a number of winters outside in the Rock Alpine Garden. I think it makes a great trough plant, and I can imagine it as a bonsai, too, but I’ve been afraid to leave it outside in my garden. Winter here is not the same as winter in Denver. Still, it survives in an unheated cold frame, and that says something about its hardiness. Our cold frames protect plants from wind and dessication, but not from cold! The potting soil in the pots is frozen solid right now, I checked yesterday.
The solar greenhouse was the first greenhouse we built at Perennial Favorites, and it cost less than $500. That was many years ago, and everything costs more now…but if you can figure out a way to build your own greenhouse, you won’t regret it. On sunny days it’s as good as a trip to Hawaii. You can putter around your flowers, or sit a lawn chair by the winter lettuce, and nibble your way to happiness.
For more inspiration, check out Penn and Cord’s website. They are greenhouse builders and growers extraordinaire! http://pennandcordsgarden.weebly.com/greenhouses.html
