The gardener’s vocation entails staying in tune with nature’s rhythms, which often means beating one of nature’s most challenging events: the late frost. Gardeners anticipate a late frost like a solitary walker peering over his shoulder when traveling down a dark alley. Jefferson County lies in Zone 6 on the United States Frost Zone Map, with an average late-frost date falling between March 30 and April 30. You never know if the assailant will appear, but it is better to be prepared then caught unaware. According to many garden authorities, it’s best not to risk the frost at all. Scott Horton of Smoots’ nursery, says, “Go ahead and get your beds ready, dress them with some top soil or mulch, and pull weeds, But a good rule of thumb for our area is to hold off planting until Mother’s Day.”
It’s another story with perennials. Just when warm days have things looking great, a late frost can ruin your season. During spring’s warm days, the sun heats the Earth, which radiates heat back into the atmosphere at night. The coldest temperatures are just before dawn after most of the heat has radiated upward. A night sky filled with clouds absorbs heat and helps reflect it back to Earth. Calm, clear nights, pleasing to the astronomer, pose the greatest danger to the garden. On these nights there is little wind to blend rising warm air with falling cold air, and no clouds to trap and radiate the heat.
The best way to avoid frost damage is to plant varieties that can withstand frost. Pick the brain of a good nursery person or take a look around your neighborhood and see what thrives. Horton suggests planting pansies or kale since both are hardy varieties for our climate. Once you have selected the plants best-suited to your location, follow the weather forecast. When frost comes, you want to know ahead of time. Even the easiest of frost-protection measures takes planning.
According to the University of Arizona’s Frost Protection Guide (UAFPG), keeping plants well-watered is the first line of frost protection. Injury from frost occurs when ice crystals form on the leaf surface and draw moisture from the leaf tissue—causing dehydration. By watering, the gardener can decrease dehydration damage. Humidity also helps to slow temperature change.
The University of California Agriculture and Natural Resources website suggests that loose mulches and cultivated soils tend to be less insulating than tightly packed materials or soils. The air spaces in these soils causes rapid heat loss. Loose mulch also limits the soils ability to absorb heat.
More extreme measures of frost protection range from using fans to create breezes, which keep cold air from settling, to covering plants with cloth or paper to insulate them. Covering plants before dusk also helps trap heat radiating from the soil. If you don’t have time to make frames around the plants, say local gardeners, drape a cover of newspaper, cardboard, plastic tarps, bed sheeting, or any lightweight material directly onto the plants. Remove the covers in the morning, once the frost has thawed, to let the light and fresh air back in and to prevent overheating by the sun.
Gardenhelper.com suggests painting plastic milk jugs black and filling them with water. Water loses heat more slowly than soil or air. They suggest placing the jugs throughout the garden to allow collected heat to radiate throughout the night. Potted plants should be brought in because their roots are unprotected. If this is not possible, mygardenhelper.com recommends wrapping potted plants in burlap or bubble wrap.
If these strategies fail, expect your garden to show signs of damage. Death of fruit, flowers, and dormant flower buds are symptoms of frost damage. Leaves, shoots, and stems may also die back. Greenwood nursery.com highlights a common theme heard from gardeners: Be patient. Nature can take a while to help plants recover. Fight the urge to do anything too drastic. Water your plants after a frost attack. They will need water to help them re-leaf after losing the first tender leaves to frost. It is better to avoid any major pruning on frostbitten plants because they can take up to a year to return to their normal growth pattern. And pruning, like fertilizing, can add to the stress.
Late frost is nature’s random way of reminding the gardener who is in control. Still, the best strategy for protecting annual plants from frost is to wait until after Mother’s Day to put them in the ground.
