I had first posted these instructions on February 24th and March 13th 2019: How to turn milk jugs into mini-greenhouses. Since I use milk for cappuchinos, I save the plastic jugs throughout the year.
Preparing the ½ gallon and gallon milk cartons for starting seeds:
- using a mat knife, cut them horizontally just under the handle. Pierce holes on the bottom of the bottom half. Invert top and put aside. Keep individual units together. I have found that I can never make a straight cut, so each one is unique.
- Procure a big bag of peat moss, and a large bag of vermiculite or perlite. I have my own buckets of compost I’ve kept defrosted since the late autumn. I’ll make a mixture of these three ingredients, moisten, and get ready to plant.
- Before planting, I have to sort through all the seeds I’ve saved and bought, a continual organizing process every spring.
Since it is too cold to work outside, I’ll spread newspaper in the studio, and fill each of the seventy-five or so plastic jugs that I have with the planting mixture. It’s not difficult, it’s just that everything takes time, more time than one thought possible. It’s important to make sure each the contents of each container is moist, but not wet. I make the mixture in left over five gallon white buckets. Make a bucketful, fill the jugs, see how many times I have to repeat that.
Have ready: white duct tape, clear tape, and waterproof markers. I made the mistake one year of unwittingly using markers that soon blurred beyond recognition, thus making it difficult to know what to plant where. I’ve solved that problem. Not only to I use permanent markers, but also now use clear waterproof tape on top.
Planting a few seeds in each jug fit the top half on the bottom and use the white tape to make sure it fits snugly. Write what you have planted and date. Put clear tape on top of that. You have created a little personal greenhouse, the only opening for moisture and air, the pour spout.
Put all the containers outside in the elements in a sunny location. Yes, that means in the snow, rain, or cold, whatever. Do not let them dry out if there is too long a dry spell. The seedlings will sprout later in the spring, when they are ready. They will be among the hardiest plants in your garden. I have used this method for both vegetables and flowers to great success.
Good luck.
Last year, 3/22/2019, there was snow on the ground when I put them out:
Later in the spring, when the time is right, the plants will sprout. You will know when the right moment comes to open the container, letting the seedlings adjust to there ambient air before dividing and planting. 
