This is the time of year when we expect to see the color of tree leaves change and drop to the ground. The fall leaf color adds beauty to the landscape and provides kids the opportunity to make leaf piles to play in (getting them to bag them is another story). However, when people see needles falling from their evergreens, they become concerned and worried their evergreens are not healthy. Since I have had a couple of calls regarding needle loss, I thought this would be a good topic for this week's column. If you have observed needle loss on your evergreens this year, don't worry, needle loss on evergreens is quite common and normal. We generally don't notice the loss because not all needles are lost each year.
Although most conifers stay green all year, they don't keep all their needles all the time. Just like the oak trees lose their leaves; most evergreens also drop needles - but not all of them. While an oak tree grows all new leaves every year, most conifers grow a new tuft of needles on each branch, to add to the several years' worth of needles it still has. Each year in the fall, it loses the oldest needles (those closest to the trunk). This is called seasonal needle loss or fall needle drop.
Some of the most noticeable examples of seasonal needle loss occur on white pine and arborvitae. The innermost needles turn bright yellow before dropping in the fall, and usually the ground under a white pine is covered with fallen needles, even though the tree is perfectly healthy. The fallen needles can serve as natural mulch under the tree.
Seasonal needle loss is least obvious on spruces and firs, which retain more years worth of needles, but even on these plants the natural loss can be noticeable in occasional years. Although some needle loss occurs on conifers each autumn, it tends to be more noticeable on some trees than others and more pronounced in some years than others. It is not unusual for needle loss to go unnoticed for many years. Stresses such as heat and drought seem to make the needle loss more severe in years like this year.
Sometimes brown needles on an evergreen really do mean trouble. Problems such as insects and diseases, or other stresses such as transplant shock, improper planting, drought or winter desiccation can turn evergreens brown. Needle browning that occurs anytime other than the fall or that includes needles other than the oldest, innermost needles, should be checked out. Some diseases cause browning of a few branches or only the bottom branches or the newest, outermost growth.
Death of the oldest, innermost needles on an evergreen in the fall may be alarming, but in most cases, it simply reflects the normal growth of a healthy tree.
Background information for this column came from a past article in the Horticulture and Home Pest News newsletter. For more information, contact the Grundy Office of ISU Extension at 319-824-6979.