Results on Overwintering Plants

Pop-up greenhouse

Last fall I moved a number of plants indoors for the winter, and others into my little pop-up greenhouse.  Those I cherished most, or were most in need of warmth, like the lemon tree, geraniums and  the jasmine, ended up in the house.  Other plants that went into the greenhouse for the winter included one pot of mint, a potted patio tomato, the papyrus plant from the pond, petunias, rosemary, basil, parsley, and the stacking planter of strawberries.

This greenhouse is just a layer of heavy plastic, and is unheated, so it has been an interesting experiment to see what difference it could make in helping plants survive the winter.


Here in southern Kansas, it is hardiness zone 6, which means it typically gets as cold as 0 -10 below zero Fahrenheit in the winter.  I had read that a cold frame that was two layers of plastic with air between could protect plants enough that it was like two zones warmer in the winter, which would make it like an area that only gets to 10-20 degrees in the winter.  So I added a layer of bubble wrap inside the greenhouse on three sides and the top, though not across the front with the door where I would need to go in and out to water. 

Left: mint that stayed outdoors all winter
Right: mint that was in greenhouse

I have also read about solar greenhouses, where dark-colored containers of water absorb solar heat during the day, and re-radiate it at night to help keep a greenhouse warmer than outdoors.  So I added small plastic containers (1-2 gallons) painted dark colors and filled with water along the edges of the greenhouse where the sun coming through the plastic walls would heat them.

All of the plants moved into the greenhouse flourished much longer than those left outside. The basil was the first to die; in early December as I recall. The tomato plant continued to live and bear a few tomatoes into December before it succumbed to the cold.  (Fresh homegrown tomatoes for Christmas, anyone?) The petunias lasted about that long as well.

The mint and parsley slowed their growth, but stayed green all winter; I was able to harvest a few sprigs along for use in cooking.

This spring, the mint returned to active growth much sooner than the similar mint plants left in a sheltered location outside over the winter.  The rosemary and parsley are flourishing.

Stacking planter with strawberries

The strawberries in the stacking pots did fairly well.  Strawberries in the ground are winter-hardy, but I wondered how they would do in the stacking planter, where the roots had such a small volume of soil to insulate them and to protect them from the cold. I had left it outside the winter before, and practically none of the plants survived.  This past winter, in the greenhouse, nearly all of the plants survived.

Although the pop-up greenhouse is not at all like a "real" greenhouse with double-pane windows and a heat source, it does make a real difference in the survival of plants through the winter.  It is also very useful in hardening off plants.  It has been a worthwhile and affordable alternative to the full-fledged greenhouse I hope to have someday.