Protecting your spring plants from low temperatures and high winds

When it comes to gardens —- flowers or vegetables — there are two elements of eastern Idaho’s spring weather that should be considered every year — temperature and wind.

Temperature

Temperature can be broken into two subcategories — air and soil.

Air temperature

Eastern Idaho ambient temperature fluctuates a lot in the spring. There will be several days of balmy 60, 70, or 80 degrees.

Then a cold front moves in and frosty or freezing temperatures take over. The average last frost in Idaho Falls is around May 22, Pocatello is May 16, Ashton is June 11. Keep in mind, that is average and there may be a later frost in any given year. This is most critical for tender plants such as tomato, pepper, squash, beans, cucumber, zinnia, heliotrope and impatiens.

Some plants survive light frosts and can be planted any time around, or shortly before, the last spring frost date, including carrot, potato, corn, beet, cauliflower, petunia, marigold, nasturtium, and lobelia.

A few will survive temperatures as low as 24⁰F (some even colder), and can be planted 4 – 6 weeks before the last spring frost date. These include spinach, broccoli, leek, onion, garlic, pea, radish, kale, cabbage, Brussels sprout, and kohlrabi.

If you decide to plant early, plan on protecting your tender plants. Local gardeners are quite creative with their plant protection devices. A simple low tunnel with a row cover of a spun cloth such as Reemay or Agribon type material can offer several degrees of protection. If you place a gallon jug filled with water between the plants under the row cover, you can overcome temperatures in the low 20s.

Other protection devices could be a Wall o’ Water, cloche, milk jug with the bottom cut off, or even a bucket over the plant when it gets cold. Whatever you use, be sure to anchor it against the wind.

Soil temperature

Cold soil temperatures may slow down plant growth even if ambient temperatures are warm. The soil in a raised bed will warm faster than the surrounding soil. Clear plastic over the soil will raise soil temperatures. Cold frames, low tunnels and plastic mulch will also bring up soil temperatures. A high tunnel is an excellent way to raise soil temperatures over a large area if you are willing to make that investment.

Wind

The average top wind speed in Idaho Falls is 21 mph. The worst of that is in the spring, with frequent gusts over 60 mph. This kind of wind destroys young plants, whether they are hardy or tender. Narrow-leaved plants, such as onion, leek and garlic are less affected by the wind.

The good news is that all the devices mentioned for frost protection will also protect young plants from the wind. So even if you plant at a schedule that will reduce the chance of frost damage, you will have more success if you also guard against eastern Idaho spring winds.

Welcome to eastern Idaho, and protect those plants from our gusty winds and late spring frosts.