Native plants, though unpopular, rarely get shocked by changes in the weather
As the saying goes: Everybody talks about the weather, but no one does anything about it. Take the coldest time of year. Do you know how low the mercury really plummets?
This is no idle question for a gardener, because the coldest night of the year puts a major limitation on what plants we grow. And gardeners never seem satisfied growing only native plants, which are rarely caught off guard by the weather.
For a rough estimate of how much cold to expect in winter, consult a U.S. Department of Agriculture hardiness zone map. You’ll find this map, showing the United States overrun with squiggly lines connecting locations with the same minimum temperatures, in the back of most gardening books and magazines.
Note that these minimums are averages. Some winters will be colder than the average, others warmer. And your plants will respond to actual temperatures, not the expected average temperature.
Don’t fault the map if your hybrid tea rose dies when it was supposed to be hardy. The map is not detailed enough to account for microclimates that differ from neighborhood to neighborhood. Wind, elevation, change in latitude, and nearness to water or buildings can push the temperature a few degrees one way or another. All other things being equal, the temperature drops a degree — and spring arrives four days later — for every 70 miles north you travel or 400 feet you climb. But not always. When the air is calm, low-lying areas can be the coldest spots. That’s because cold air, being heavier than warm air, flows downward — perhaps right into your garden. So even if your garden and a friend’s are in the same general hardiness zone, microclimates can make actual temperatures different.
Do you know what temperatures really are in your own garden? Glean this information by getting an accurate thermometer, then mounting it at a suitable location. Keep it off your house, where it will pick up radiating heat, and out of the sun. The north side of a gatepost to your garden is ideal.
Because lowest temperatures typically arrive late in the night, then creep away by morning, make sure to bundle up and go outside at about 4 a.m. whenever you think the night is really cold. A better idea is to purchase a minimum-maximum thermometer, which records — until reset — the high and the low temperature.