With low temperatures threatening to again fall around freezing this week, it's a good time to learn how to revive "frozen" plants. Photo by Rita Bricker

By Rita Bricker

Rita Bricker

Warmer weather is coming, so what can we do about those ugly, shriveled and dried plants that suffered from the cold over the winter? We can repair them, that’s what.

What happens when it freezes? Light frost (32 degrees or slightly above) occurs when water vapor freezes on the surface of plants. It generally causes only cosmetic damage to leaves on all but tropical plants. A hard frost, on the other hand, freezes water in the plant cells, dehydrating the plant. When the warming sun comes up, those tissues defrost quickly and burst, killing leaves and stems, and even creating cracks in the bark of some trees. Plants appear limp, dried out, or even blackened.

So how can we revive those damaged plants?

Rule 1: WAIT! The average last-frost date for our zip codes in climate zone 9 occurs during the month of February. In fact, there is a 50-percent probability that our temperature could drop below 32 degrees as late as March 6. Be patient and watch the weather projections for frost events before attempting to revive damaged plants.

Rule 2: Continue gently watering your plants as normal because frost has sucked the moisture from the tissues. But do not over-water, as that could stimulate growth in a plant that is in a weakened state.

Rule 3: Resist the temptation to fertilize your plants at this time. As with over-watering, this could stimulate early growth in an already-stressed plant.

How can you tell what’s dead and what is still viable? Scrape a stem or an area on the trunk. If the underlying tissue is green, it’s alive; if it is brown it’s dead. You can also try bending a branch. It will break if it is dead, but flex if it is still alive.

If just outer growth shows damage, lightly prune affected areas, trimming off dead flowers, leaves, and branches. Cut back damaged stems a few inches into healthy wood, but don’t remove more than is necessary. Renewal pruning is called for if most of the upper growth is damaged; this means severely cutting back affected areas to within a few inches of the ground. If any part of the plant is black, slimy, mushy, or smells bad it needs to come off.

Cactus can freeze completely in a short period of time, so throw out any that has blackened or turned mushy as it will not recover. It may be hard to gauge damage to succulents like agaves until summer because they may continue to grow from the central bud deep within the plant even if there is extensive damage to the outer leaves, so give them some extra time.

And if you need to replace freeze-damaged plants, keep in mind that our Master Gardener plant sale is coming up on March 2. We will have a great variety of hardy locally-grown vegetables, flowers, and cactus/succulents for purchase at reasonable prices.

This column appears in the February issue of InMaricopa.