Sunday, September 23, 2018

Fall Needle Drop by Mary Small

Fall needle drop on Black Hills spruce, photo by Donna Duffy

Spruce trees often get attention in the fall. Their inner needles turn yellow or brown and drop off. To put your mind at ease, it’s not unusual for these conifers to shed interior needles beginning in late summer and continuing well into fall.  This is normal evergreen behavior. 

In fact, all conifers (“evergreens”) including spruce, pine, fir, juniper and arborvitae lose their oldest needles every year. Contrary to what the name implies, “evergreens” are not really green forever. Their needles generally have a 2–4 year life span, although spruce trees live about 5-7 years. 

While needle loss occurs every year, the process is usually gradual, over a period of several weeks or even months, depending on species and weather. It’s so gradual, that you might not even notice the needle drop. Some species can shed needles in a fairly short period of time, making it look as though they’re in serious trouble. And environmental problems, like drought, can make needle drop happen more quickly than it would if the tree was healthier.

There is no need to treat evergreens for this condition.  This fall and winter, ensure all evergreens are irrigated monthly in the absence of rain or snowmelt. Apply water so it reaches the absorbing roots.  For established plants, these are located a distance of two to three times the height of the plant away from it. For newly planted trees, apply water to the planting hole and just outside it. Always irrigate when the soil is unfrozen and able to absorb the water.  Studies show that fall-applied water has great benefit.  Roots are still active and can absorb water as long as soil temperatures stay above 40 degrees Fahrenheit. 

If evergreen needle drop is occurring on outer needles or both inner and outer needles, a closer look is needed.  Branch samples may be brought to the Jefferson County Extension Plant Diagnostic Clinic, located on the Jefferson County Fairgrounds, for diagnosis.  Jefferson County residents will be charged a $7 fee, non-Jefferson county, $10.

For more information, check out these CSU PlantTalk resources: