Winter sowing with milk-jug mini cold frames

In recent times, some people are experimenting with homemade outdoor mini cold frames made from gallon milk jugs and plastic takeout containers — especially those sold with rotisserie chickens (left).

Every seed has a mechanism to keep it from sprouting in the wrong place at the wrong time. In the case of seeds that are in moist fruits, like these Jack in the pulpit’s, it is the ripe pulp that inhibits germination until it naturally breaks down by cold destroying the natural hormone that inhibits germination, freezing and thawing and microorganisms. I can wash the fruit off and the seeds will sprout right away.  Not all seeds need their fruit removed, but most of the hardy plants seeds need to go through a period of cold, or warm and cold and maybe warm again to germinate. I could use the refrigerator, but it is much easier to let nature do the work.

 

I made flats with openings in the bottom and medium sown with lots of seeds, for example, tiny perennial primrose seeds or hardy annuals like Nicotiana or opium poppies. I’d cover the flat with an inverted flat with small openings and place it in the shade, but where gentle rain and snow would sift onto the seeds and medium. If I couldn’t find a flat with small openings, I would fashion wire ½ inch hardware cloth cover to keep critters out (left). That would be necessary for sowing something like acorns.

Serious seed sowers like rock gardeners and professional botanical gardens, sow individual varieties in three- and one-half inch plastic pots and place them in a cold frame that remains open but is covered by screen or a similar open material (left). We’ll have to check that the pots do not dry out – especially when seedlings appear.

 

 

 

The way to make the gallon jug for seeds starts by making holes in the top for ventilation and in the bottom for drainage. I use a screwdriver heated on a gas stove but a power drill will work as well.

 

 

 

I measure about four inches up from the bottom and make several marks around the jug. Next, draw a line around the jug, but leave a space at the handle for a hinge.

Next, I make a small cut in the plastic with a box cutter, and you could use the knife to continue the cut, but I find inserting a pair of scissors is easier to guide and safer. 

 

You can see how not cutting all the way around makes a hinge by the handle. Use a piece of tape to temporarily close the cut jug. Remove the cap for more air circulation.

 

 

 

 

Here you can see the results with containers made by Joe L’ample. He fills the containers with about three inches of moistened sowing medium. I used commercial sowing medium with some added coarse perlite.

Sow seeds to a depth recommended on the packet. Close the container and duct-tape it shut all the way around. Place the jugs outdoors in a sheltered spot out of full sun, but where they will get bright light and cold.

When the seeds have germinated, cut a window in the jug to keep them from heating up too much, or open the jugs during the day and close them at night. Another helpful result is that these seedlings will not need to be hardened off by taking them inside and out every day for weeks. They are ready to go into larger individual pots, or ins some cases, right into the garden soil.