Purdue Extension Service

Vanderburgh County, Indiana

Recent Frosts Not Expected to be Disastrous

By Larry Caplan, Extension Horticulture Educator, Vanderburgh County, IN

For the Evansville Courier and Press, April 12, 2009

The frost event we had last week worried a lot of people. And rightly so: the frost followed several weeks of spring-like weather, and everything was in full bloom. As it turns out, I think our gardens may have dodged a bullet, and will come out in good shape this spring.

The cold snap cannot be considered a "late frost." It actually occurred right on time! The average last frost for the winter is during the week of April 6 to 15 for most of the southwestern Indiana counties hugging the Ohio and Wabash Rivers, and April 16-25 for the rest of southwestern Indiana. During these dates, on average, we see our last frost of the year, although there is still a decreasing chance of a frost up to two weeks after these dates.

What caused all the panic was the month of spring-like weather, with temperatures well up into the 70s, before the frost. This brought nearly all of our fruit and landscape trees and shrubs into leaf and/or full bloom, probably the most delicate stage of growth they could be in, as far as frost injury goes.

This was very similar to what happened in 2007, when we had record low temperatures down into the teens on Easter weekend, after a month of abnormally warm weather. Unlike 2007, though, our temperatures didn't dip much lower than 30 degrees in Evansville, so while we had the potential for disaster, we luckily didn't get exposed to damaging temperatures.

For the most part, I expect that by now all we are seeing are some frosted leaves that may be a little brown or black along the edges. We probably lost a few blooms on apples and peaches, but that's OK! Fruit trees routinely produce way more blooms than the tree can support, and gardeners and farmers need to thin out the excess fruit to get a high quality crop. The frost merely helped a little.

Probably the plants that got hurt the most were tender annual flowers and vegetables that were planted much earlier than is recommended. I understand the desire to get out into the garden and start planting SOMETHING when the weather warms up, but tomatoes and most summer annual flowers cannot tolerate temperatures at or below freezing.

This is why Purdue offers a free publication entitled the "Indiana Vegetable Planting Calendar". It illustrates when the safe times are to plant over 50 common vegetables. Some gardeners complain that these dates are way too conservative, and that they can get their gardens in much earlier than that. Maybe so; but if you follow these guidelines, you won't have to spend money on frost prevention items, or replanting the garden.

For more information on gardening and frost protection, contact the Purdue Extension Service at (812) 435-5287.