Cold frames and grow racks can serve as miniature greenhouses for people without a lot of gardening space. They can be used on roofs, patios and balconies, although some cold frames on the market are actually a greenhouse by another manufacturer's definition, mainly by virtue of their size and price.
For about $70, you can get a 4-tier grow rack with a powder coated steel frame and vinyl cover with a zippered door and adjustable shelving. Some grow racks are quite attractive as well, and make a nice addition to a patio, deck or gazebo. What a great idea for a Mother's Day or Easter present for the green thumb in the family!
Cold frames for starting your seedlings or prolonging your herb garden season are really quite easy to make yourself with a few pieces of plywood and some heavy plastic.
For durability, use a naturally rot-resistant wood like cedar, and a salvaged storm window for the cover. If you paint the inside of the walls of the cold frame white or silver, it will increase the amount of light inside the frame, but be sure to use paints or sealers that are not toxic for your plants.
You'll want to situate your cold frame on well-draining ground and orient the window to face south for maximum sunlight exposure.
To learn more about the greenhouse cold frames and grow racks, check out the shopping links at the top of this page.