LONGMONT – Rollercoasters aren’t high on my list for fun rides and I’m not at all fond of wet, freezing weather. So the spate of hot-cold-hot at the end of April has made a rather grumpy gardener out of me as I worry about my apple trees and awakening perennials.
Had it only been snow to blanket the landscape things would have been fine. But the wet, watery storms came with a blast of temperatures in the very low 30s, which for buds isn’t so harmful. But for fruit tree flowers is a nerve wracking thing.
Many plants awoke with the early warmth, stretching stems or leaves into the sunshine. Tree buds swelled and some even broke, covering branches with tender new leaves. This is fine; in many cases, the early growth of perennials and bulbs isn’t harmed by a frosty nip because the tissues are fairly hardy. Tree buds are able to withstand cold temperatures.
But once buds begin to open, they lose much of their cold hardiness; the more open they become, the less tolerant they are of frosts. Cherries, peaches, and many apples were close to flowering when this frozen blast hit them.
If the freeze hits the flower for a half hour or longer, damage to the fruit can occur. Check to see the extent of the damage to your tree. At or near blooming, freezing temperatures of 28 degrees Fahrenheit will result in about a 10-percent loss of flowers and fruit; at 24-degrees F a 90-percent loss. Several hours after a freeze and once the tissues thaw, the undeveloped fruit become brownish-black if they were damaged or killed by the cold.
If your cherry or apricot was in flower, check it for damage. The flower contains a single pistil – the female part of the flower that becomes the cherry or apricot. It’s cupped by the sepals and petals of the flower. If the pistil is brown or black, it was killed by the freeze and won’t become fruit. If it looks healthy and green the fruit is alive.
Apples have clusters of flowers, the center-most of which is the most developed. Known as the King bloom, it is the first to open as a flower. The king bloom develops the largest fruit and is considered the most desirable of the flowers to flourish. But it’s also the most likely to be killed in a frost since it opens first.
Checking for freeze damage to apples is slightly different than checking cherries or apricots. Apple pistils are located inside the base of the flower, making it necessary to tear the flower apart to see if the center of the flower is brown or black. Check both the king and side blooms separately; hopefully some of the side blooms weren’t harmed by the freeze.
Check a few of the flowers to see if your fruit crop was harmed by the ice, but don’t rip apart all of the flowers. Take a sample from various parts of the tree to give it an overall checkup. Then keep an eye on the weather because nature hasn’t settled down yet for the warmth of summer.
By Carol O’Meara, Colorado State University Extension. CSU Extension together with Boulder County Parks and Open Space, provides unbiased, research-based information about consumer and family issues, horticulture, natural resources, agriculture and 4-H youth development. For more information contact Colorado State University Extension at the Boulder County Fairgrounds, 9595 Nelson Rd., Box B, Longmont, 303.678.6238, e-mail firstname.lastname@example.org or visit ext.colostate.edu/boulder.