Great for winter sowing or just getting a bit of a jump on the season when overnight frosts are still a possibility, these mini greenhouses are quick and easy to make with 2 bottles from the recycling bin.
If you've never heard of winter sowing, head over to wintersown.org for the scoop. The basic idea is that instead of the time/resource intensive methods of starting seedlings indoors before transferring them outside, you just chuck your seeds outside during the depths of winter and when conditions are right they will sprout by themselves. Providing the seeds with an enclosed environment that traps heat but still lets in the rain and lets excess moisture drain away allows the seeds to sprout earlier than they otherwise would, giving you a jump on the season with very little work or expense.
But if you missed your chance to sow the seeds in winter (oops!) you can still start your seeds during the spring as much as a month or two earlier than you would be able to plant them unprotected. Just be sure to dribble a little extra water inside if the soil looks dry, and to remove the top on unexpectedly hot days so that your seedlings don't cook. If you normally plant seeds indoors, try putting some outside at the same time and compare the results.
There are lots of different styles of recyclable containers you can use. This article covers one particularly convenient one made from two 2-liter soda bottles.
First rinse out two bottles and use scissors or a utility knife to cut them each in half.
Take one top part (A), turn it upside down and put into a bottom half (B). Take the other top half (C), cut a slit part the way up (shown in red below). Spread the slit slightly so that the top half can now slide snuggly over the A-B assembly. D is not needed.
Note that your cut should be situated so that the mouth of (A) is at least an inch or two above the bottom of (B), so that excess moisture can drop down into the resevoir.
To plant, remove the top, fill (A) with soil, water and place your seeds at the proper depth. Put them outside where they get some sun, preferably in a crate or otherwise wedged into place so that they don't get blown over.
Be sure to label your containers, unless you don't mind being surprised!
Before you know it, you'll have some hardy seedlings ready for transplanting to their final locations. Keep the bottle tops handy for a while; you can pop them over your seedlings if a late frost threatens wherever they happen to be planted out.
Good luck, and happy gardening!