Living in Southern Texas, I tend to forget that this time of the year is supposed to be cold. We are still hitting 90+ regularly here after all. Still, I learned a lot from years of living in Northern climates. The great destroyer is frost. Light frost will kill off most annuals and all tropicals. Hard frost kills back just about everything that isn’t an evergreen.
Sure, Texas isn’t suffering from much of that problem. In truth, I have been working out ways to encourage more light frosting locally to improve the quality of kale, cabbage and other Brassicas. Still, most of the US is suffering from impending frost or has already gotten it. The most common solution is row covers. These allow air to flow freely, let in light and still keep out the frost.
A recent conversation on a forum brought to my attention that at least a number of people didn’t know of any other methods to prevent frost. Short term freezes in the garden itself can also be prevented by spraying down your crops with water. It sounds counter-intuitive, but when you spray plants with water right before a freeze, the water itself leeches heat into the plant while in the process of freezing and prevents the plant itself from freezing. It only works for a very short time, but can often stave off minor assaults by Jack Frost.
The method I prefer is simply finding a way to create an overhang where air movement is limited. Seven feet up, the structure can still hold back light frosts with ease and even prevent some heavy frosts from hitting. It doesn’t prevent the ground from freezing, but for plants that are winter hardy, it can prevent leaf loss. (Leaves, you know, like your kale and cabbage.) You aren’t going to save a tomato this way, but you can save a number of other plants. I’ve managed to keep an annual alive through the winter to become a biannual this way.
The evidence of it working can be found in most homes. More accurately, on the front of most homes. A porch with an overhang and where wind doesn’t blow through any long openings is perfect. Put a few plants at various points on the porch through the winter. The ones on the outer edge will still catch some frost, but the closer to the house you are, the less frost there will be. Ambient heat from the house doesn’t hurt, but if you have a well insulated house, this should still be effective. This effect is sometimes seen under large trees with full branches. Frost will form on the boughs of a pine, but not on the spot under them most of the time.
Have something you want to keep going, but know winter is going to take away prematurely? Pot it up and keep it on the porch. It probably won’t live through the whole winter, but you can certainly extend its lifespan by keeping the frost at bay. Another option is to add thermal mass around the plant. This can be especially successful if there is a reflective surface between the plant and the sun, with the thermal mass behind it. Through the day, the thermal mass is collecting solar heat and at night it is releasing it.
Done well, plants can gain several planting zones northward in their survival ratings. You may not have the funds or space to dig a pond and set up a large thermal mass wall, but you can probably stack a few dark stones around your plants to help keep the air warm enough around them that frost won’t form there. You won’t be affecting the microclimate enough to make a huge impact, but it should at least have some measurable difference between the spots where you do this and other parts of your property.