After a long Minnesota winter, most of us can hardly wait for spring blooms and early vegetables. Aside from spring flowering bulbs, you can add some early color and interest to your landscape with cold-tolerant blooming annuals. Since early spring always holds the chance of frost, choices are limited to annuals that are hardy. But, as you will see, there are many from which to choose.

Some annuals have a built in ability to survive much colder temperatures than others. The key to making use of a plant's cold tolerance is to acclimate it before planting. Ask when you buy your annuals. If you find them displayed outdoors, they are probably already acclimated, but ask to make sure.

If you buy tender plants or have grown your own, you will need to acclimate them to insure their cold tolerance. Begin by keeping the plants outdoors during the day any time the temperature is 40º or warmer. After several days they should be able to handle the cooler temperatures. Be prepared to move the plants indoors when the weather changes, especially at night. Depending on the variety, once acclimated, these plants should be able to withstand a light frost.

Cool weather annuals thrive only when the weather is cool. Once it gets hot, they are done for the season. Cold tolerance is simply based on the ability to withstand low temperatures. Some cold-tolerant annuals are also cool weather plants, peaking by early to midsummer. Examples of cold-tolerant/cool weather plants are spinach, lettuce, radishes, peas, pansies, godetia and calendula.
In our area, most gardeners have good luck with snapdragons and sweet alyssum. Petunias, too, are actually fairly cold tolerant when acclimated and some varieties will bloom on and on.
Acclimated pansies can tolerate several degrees below freezing, so they are usually the first to be planted. Most other bloomers tolerate light frosts, but not freezing. Acclimated cold-tolerant vegetables can be planted as soon as the ground is workable.

All the annuals mentioned will do fine in containers, but keep in mind that they will not have the benefit of the warmth in the ground to help them on cold nights. You might want to wait an extra week or two before planting containers, or fill them with the hardiest of the plants available.
Covering the plants with something lightweight will give you a few degrees insurance. Be sure to remove the cover before the sun hits the plants Watch for white patches on the leaves. That happens when either the plant was not fully acclimated or it was just too cold. Give the plant a few days to recover, then snip out any leaves that are still white or have browned.

There are things to help increase the cold tolerance of my annuals. Keep them as healthy as possible. Make sure they aren't water stressed and fertilize very lightly while it is still cold to avoid lots of tender new growth. You may also find that annuals that withstand 2-3 degrees of frost in the fall are damaged when it gets that cold in spring. Why? Growing through the season, plants become very adaptable and tough and they have had time to adjust to the gradually cooler temperatures before a frost hits. Annuals that have been properly acclimated in spring are young, with tender tissue, making them less tolerant at that point in their lives.

Wall-O-Water really works when used according to directions. It provides about a two week head start on the season. The key is to follow directions, set up early and let them warm the soil for several days before planting. There are several other types of caps and covers that will offer a few degrees of protection, but Wall-O-Water can offer as much as 15-20º.