Earl

If you are thinking about wintering the trees, you don't need lights for the juniper or maple or willow because they are dormant. The only reason to use a greenhouse for "outside" trees is to keep them freezing too hard. Check out the many threads about wintering trees.

I don't think you would need lights for the Dracena, either. I'm no great expert but i think light until 3 or so would be fine. Heat would be more of an issue. They can't taking freezing or even near freezing--needs house temps.

Now if you are going for tropical plants in general to get real bushiness you may need more light but flourescents aren't going to do it, unless it is for one or two trees. They have to be just inches about the trees to do any good. You will need halogen or one of the other very bright greenhouse lights. Check out greenhouse sites like Charlies. Or start doing searches on greenhouses and you will find out all sorts of good info.

Don't know if that helps or not. If not, give us more info about why you are thinking about a greenhouse, your climate, whether you plan to heat it, etc.

Earl