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Protect plants from late spring frosts

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By Dennis Morgeson

We know far too well that late spring frosts and freezes are very common in Kentucky. These late frosts always seem to follow a long warm stretch that has made many of our trees, shrubs, flowers, and fruit trees start to grow. Nurseries and garden centers sell tomato plants among many other frost sensitive plants much too early.

Homeowners buy frost tender plants on a warm April day when it is in the 80’s thinking frost is long gone only to have their prized plants killed two days later. This is great business for the nurseries, however, not so great for the gardener on a budget.

The terrific thing about trying to force the season is knowing that there are several things you can do to help protect your plants. Keeping your plants just a few degrees warmer than the air temperature can mean the difference between a nice harvest and beautiful flowers or brown dead plants with no fruit. Below are some general procedures that may help increase the likelihood of you plants surviving a late spring frost.

 • Water your garden well before nightfall. Humidity slows     temperature change. The soil will release moisture during the night, and keep the air around your plants somewhat warmer.

 •  Even the slightest breeze can keep frost from forming when the temperatures are at the threshold of freezing. By keeping the air moving, it keeps colder air from settling around your plants, which will keep frost from forming. To keep the air moving, position a fan near your plants. Be sure to protect the fan and the connections from the elements.

 •  Cover your plants before it gets dark. By covering your plants when it is still light you are trapping some heat around your plants. This residual heat can keep the temperature around your plants above freezing at night. It is best to have a stick or frame to keep the covering from actually touching the leaves of your plants. Be sure to allow the covering to touch the ground on all sides, this will trap more heat. Use a light weight material such as newspaper, blankets, bed sheets, or remay fabric (tobacco canvas). If you use plastic don’t allow direct sunlight to shine on it in the evening when you apply it, or in the morning before you take it off. Just a few minutes of direct sunlight on plastic can cause the temperature to spike under it to well over 100 degrees F.

 •  A burning light bulb can also help keep plants from freezing. Be sure not to allow it to touch the foliage or trunks of plants. A light bulb under a plant with a covering over it can keep the temperature above freezing under that cover in temperatures as low as the mid-twenties.

 • Filling old milk jugs with water and allowing them to warm in the sun can also give off enough heat around small plants to keep them from freezing if they are put close to the plants and are covered with some material such as a sheet or piece of plastic.

 • Small individual plants can be covered with jars, milk jugs, paper cups, or even an upside down flower pot or bucket. Anything that can trap heat and keep frost off of your plants leaves will help.

 • Potted plants are even more susceptible to cold temperatures than plants planted directly into the soil because the entire plant is exposed to the cold temperatures not just the top. These plants can be covered like other plants, however to be safe, just put them indoors for the night. A garage or out building will work nicely.
With a little effort and common sense you can protect your plants and your pocket book from our late spring frosts. Also, avoid buying plants too early. Our average last spring frost in central Kentucky is generally between April 30 and May 5. A good rule is to wait until Derby Day before planting frost sensitive plants. We generally have 150-160 frost free days, plenty of time for growing most crops.
With all of this said, it sure is hard to resist trying to be the first in the neighborhood to get a vine ripened tomato. 

Happy gardening!