The beginning of spring does not always mean the end of sub-freezing temperatures — but growers can prepare for those cold temperatures.
According to the University of Missouri Extension, the median date for the last spring temperature of 32 degrees is between April 3 and April 9 in Butler County — meaning that it can occur later than that up to 50% of the time.
“Growers should be aware that (the median date is) an estimate,” said Juan Cabrera, horticulturist for the University of Missouri Extension in Butler County. “Something may happen that we might have a frost date later on after that. And I think that’s based on a likelihood of how often a frost happened on that date in the last 30 years.”
Gardeners define a light freeze or light frost as temperatures that fall just a few degrees below freezing for a few hours, while a killing frost is when the temperature drops below 28 degrees for a longer time. While a light frost might not affect some hardy plants, a killing frost will kill the top growth of most perennials and root crops.
Brian Hobbs, owner of Hobbs Nursery in rural Poplar Bluff, said that he has seen morning lows dip into the lower 30s as late as May.
“My father, a man of great knowledge who passed away in 2016, always told people to wait till the middle of April,” Hobbs said, “but you do get people that get anxious because of the warmer temperatures happening now.”
Hobbs advises covering plants and other tender items of vegetation with protective fabric if the temperature drops.
“If you do have plants, vegetables and other blooming items, you can cover with blankets or type of frost fabric,” Hobbs said. “A lot of times if you have a heavy frost, if you spray the frost off with water before the sun hits the plant or tree, it will melt the ice crystals from the frost, which burns the plant or blooms.”
Cabrera said that growers can protect their vegetation with row covers, which can be made from transparent bottles or milk jugs.
“They can cut the bottle and just put them on top of the plants in the evening around 4 to 5 p.m., to prepare them for the frost temperatures in the night,” Cabrera said. “Then early in the morning, they can take those jugs off because if they leave them covered during the day, they can get too hot and it might kill the plants.”
One of the more unique ways that peach growers protect their crops during cold temperatures is to spray water on the trees, which coats the leaves and buds with a layer of (ironically) protective ice.
“Orchards do use water to protect trees from damaging effects,” Hobbs said. “It actually insulates the blooms.”
However, there are some plants and crops that aren’t bothered as much by the cold.
“There are some crops that can be planted anywhere between three to six weeks before the last frost date, such as the cool season vegetables,” Cabrera said.
Cool-season vegetables include cabbage, lettuce, broccoli, cauliflower, kale, carrots, potatoes and beets.
“The reason why they’re planted right now is because they don’t do well during the summer temperatures,” Cabrera said. “That’s why they’re called cool season crops. … (For example, with lettuce), hot temperatures send a trigger signal to the plant to produce flowers and seeds, and the lettuce becomes bitter.”