A two liter clear pop bottle will make a quick, inexpensive greenhouse, perfect for starting a few seeds or propagating a plant cutting. I really like these for cuttings. They create a perfect starting climate for cuttings.
Start the project by using a clean two liter pop bottle. Use a serrated knife and cut near the bottom of the bottle. Most plastic bottles have a clear line about two inches from the bottom, where the straight sides begin to taper down.
Make the cut at least an inch above this line, so you’ll be able to fit the two sections back together. The pop bottle may want to move or pop on you so use extreme care when cutting.
Finish the cut either with the serrated knife or with scissors. I find scissors are easier for me to use.
You can place potting soil directly in the bottle bottom or use min pots. Little peat pots will work well. Some people make pots from toilet paper rolls cut down to 3 inches in height.
Plant your seeds or cuttings. If you use a rooting liquid or powder on the cutting they will root much quicker.
If needed, water the pots, and then fit the top of the bottle in place. There’s a trick to this – slide most of the top inside the base, then press your fingers against the last section to make an indent; this will enable you to slide the rest of the top inside the base. When you release the indent, that section should spring back out, creating a close seal all around. But if you don’t get a good seal, don’t worry – the plants won’t mind a little fresh air.
Set the bottle greenhouse in a sunny windowsill and observe the humidity level over the next few days. I also like to set the bottle on a TV or refrigerator if the area gets sunlight. You get bottom heat this way, which is beneficial to many plants.
A slight film of moisture collecting on the sides of the bottle will add humidity to the air in the bottle, which is good. But if water starts to run down the sides, open the top of the bottle for a while to reduce the humidity. Too much liquid will cause soggy soil and possibly soil mold.
When the last frost date approaches, you can begin setting the bottle outside on warm days. This will allow the plants to adjust to full sunlight. For the last week or so before planting, you should also remove the top of the bottle. This will let the seedlings harden off and acclimate to the sunlight and wind. This is a very important step and overlooked my many gardeners.
I also use clear pop bottle in the garden in early spring to cover small seedlings at night for protection form the cold and even insects.