Whether you're starting seedlings or nurturing full-size productive plants, a greenhouse can extend your growing season, deter pests and help your plants flourish. Greenhouses can be small for just a single seedling or large enough for a full crop.
A greenhouse allows you to start a seedling earlier in the season, making it hardier when you plant it in your outdoor garden. To make your own little greenhouse, you'll need two 1-liter soda bottles, one just slightly larger in diameter than the other. Slice the smaller plastic soda bottle a little more than halfway up, and invert the uncapped top end inside it. Fill the inverted end with soil and seeds; the soil should be no less than 3/4 inch from the top edge. Cut the bottom end off the second bottle just above the curved bottom, and use this to top the potted bottle.
Leave this seed starter in a sunny window or, if the weather is warm enough, outside. This 1-liter bottle is enough for one seedling. Two-liter and gallon bottles can accommodate two or three seedlings at a time.
Using the same soda bottles, you can cut the bottom edge off and stick the top end over a small plant in a flowerpot or outdoor garden. Be careful to vent these bottle greenhouses (remove the cap) in very warm and sunny weather, as the inside temperature can be more than 20 degrees hotter and too hot for a delicate plant to handle.
Small portable greenhouses can be made out of picture frames, old windows or even fish tanks. If using picture frames, glue, nail or tape together the frames into a long rectangular prism, with one long side open. Over the framed sides, glue glass or heavy clear plastic (as these materials will let light in). Place your structure, which should resembles a sort of see-through upside-down planter box, directly over an outdoor planting area. Alternatively, you can use this greenhouse inside and use small flowerpots with drainage and a surface onto which they can drain.
When building a small A-frame greenhouse from scratch, you'll need hinges, glass or heavy clear plastic, wood frames and triangular wood panels. The triangular wood panels will close off the opening and keep pests out. Hinge the cover to the main body so you have easy access to water or prune the plants. Note that the ground under the greenhouse will stay warmer and freeze less often than open planting areas.
Larger greenhouses can be made using garden fencing, plastic hoops and PVC piping. No matter what size greenhouse you want to build -- small and portable or big enough to walk through -- build a sturdy bottom frame first, as this will help to set the stability of your structure. For a large greenhouse set upright pipes into the ground and lashed or bolted to the frame no more than two feet apart. Connect hoops or flexible PVC from side to side using the uprights to anchor them. Run a single plastic pipe down the middle of the curved framework; use plastic or nylon wire ties to connect this. Cover the entire structure with heavy plastic sheeting, preferably one piece or large overlapping pieces. Anchor the plastic to the frame and hold down with bricks around the perimeter. Never build a flat roof, as it could collect rainwater and cause a collapse.
If you don't have a backyard in which to plant your garden, you can build a small and very utilitarian greenhouse on your patio or balcony. Use a metal open grille shelf unit. Make sure it is sturdy enough to hold the weight of several potted plants. Put the shelf unit in a sunny spot and cover it with heavy clear plastic. Use wire ties or duct tape to hold the plastic in place, but be sure to leave an overlapping flap, which you can use for access to your plants. Line the shelves with as many plants as can fit without overcrowding them. Remember that any greenhouse you build has to provide enough room for growth.
Enjoy the bountiful fruits of your labor.