What Does this Cold Snap in a Warm Winter Mean for Fruit?

Mark Longstroth

Chilling and dormancy normally prevent plants from beginning growth during warm spells in the middle of the winter.  The very warm weather we have had this winter makes me think that most plants have already completed their chilling requirement and are ready to start growing.  Over the last couple weeks I have received several calls that peach and cherry buds were swelling.  This was followed by what damage will this cause?  This means that the plants chilling requirement is completed and the trees are no longer dormant.  With the warm temperatures growth has begun.  The plants are now accumulating growing degrees.

With the return of warm weather the plant begins to grow.  Once growth begins the plant cannot increase its ability to withstand cold and will be injured by very cold weather.  This week’s low temperatures fell into the teens and we might see damage.  We can use the spring critical temperature charts to estimate damage. Fortunately the range of damaging temperatures during early growth is very wide.  Depending on the type of fruit the cold temperature required to kill 10% of the flower buds is 18 to 15 degrees.  The temperature required to kill 90% of the blossoms is at or just above zero!! 

This means that even though we have seen cold temperatures into the teens and expect some damage, there are still plenty of fruit buds available to flower and bear fruit.  I do worry about raspberries which seem to start early in the winter and suffer winter injury during winter cold spells but for other crops I am not worried.

Estimating Damage to Fruit Buds

It is very hard to estimate damage in mid winter.  Generally we need to take cuttings, bring them indoors and put them in water.  After a week or so we can assess the damage.  For peaches, the dead fruit buds will fall off.  For most other fruit plants we need to see if the fruit buds will grow.  If you are in a hurry, you can slice the bud open and see if the center in green or black. A black center indicates a dead flower.  Some fruit have more than one flower in the bud, so you may see multiple black and green tissues depending on the ratio of dead and live flowers. 

Other Types on Injury to Expect

The colder the temperatures go, or the more advanced the growth stage increase the likelihood that the bark and wood are damaged.  Assessing damage to the bark and wood is much more subjective.  Here we slice the stems and see if there is much browning below the bark and in the wood.  There is often a wide range of browning if there has been damage.  Plants can regenerate killed cells from the survivors, so estimating damage here is very hard.  Some plants that appear winter injured in the early spring will grow out of it.  Others survive but take years to recover, if at all.  Severely damaged plants may grow until we get to the hot dry part of the summer and then collapse.  Young plants are the most likely to be damaged.