Now that it's officially spring and beginning to get warm, it's time to think about how to keep your greenhouse cool during the hot summer months. Remember, a solar greenhouse is a giant solar collector, and if it's not shaded in some way, it will keep collecting heat all summer long.

If you've designed it properly, facing true south with lots of south glass and minimal glass on the east and west sides, you're off to a good start. If the roof overhangs the south side, you're even better off because less summer sun will enter the windows. A properly designed greenhouse will be ready to face a hot summer with few overheating problems.

You'll want lots of light in the greenhouse, just no direct sun light. Once sunshine passes through glass it changes from light energy to heat energy. The plants inside will still need plenty of indirect light.

You can plant shade trees in the yard to the southeast and southwest of the greenhouse. Don't plant evergreens or others that don't shed their leaves in winter or you'll also block winter sun. Plant trees that fill out with lots of leaves but will drop them all and pass lots of light through sparse branches in winter.

You can also plant tall flowers such as sunflowers along the south exterior of the greenhouse. What a perfect way to shade the glass! They'll grow about six feet tall and provide plenty of summer shade.

Any fast growing vine would also provide shade. Use a vine that can be pruned back in the fall but grows quickly in the spring. Or, plant your peas and beans along the south side. Just don't plant anything permanent that will grow tall and shade the glass during the winter.

You can also make removable shade screens. It's a bit of work, and you'll need a place to store them during the winter, but they work well, admitting diffuse light that plants love without admitting direct light.

Whatever method you choose, plan ahead. July is not the time to think about shading! You'll have to make shade screens in April and May or plant vines and sunflowers in early spring if you want your greenhouse to perform well in summer.

A final option is to design a greenhouse that converts into a screened porch in summer. Most of the glass will need to be removable (another storage problem) or you'll need to use mainly operable windows. Neither is a good option for winter as all operable and removable windows leak air. If you choose this method, be sure to purchase windows with extremely low infiltration or caulk and seal the panels of glass well in the winter.