Evergreens might also shed needles this season
It’s normal for deciduous trees and shrubs to drop their leaves in autumn. Many homeowners don’t realize that it’s also normal for evergreens, such as pines, to drop some needles.
“Needles don’t last forever,” said Sharon Yiesla, plant knowledge specialist at TheMorton Arboretum in Lisle.
“They live for a few years, and then they fall off.”
Shedding their oldest needles every fall is a regular part of the life cycle of evergreen trees and shrubs. New needles — which are actually a kind of leaf— will growin spring.
“Most homeowners don’t notice as long as the tree sheds its old needles gradually,” Yiesla said. “But they sometimes become concerned if it seems to lose a lot of needles at once.”
The needle loss is often most conspicuous on pines because of their open branching habit, and because pine needles grow— and fall— in bundles of two or more. That makes the loss more obvious.
Spruces and firs discard needles, too, but the loss is less apparent because of their dense branching and tight, pyramidal form. They also shed needles singly in the interior of the tree where it’s hard to see.
The life span of an evergreen needle depends on the tree species. White pine (Pinus strobus) has bundles of five long, slender needles that last for two or three years before they turn yellow, then brown, and drop to the ground.
Austrian pine (Pinus nigra) and Scots pine (Pinus sylvestris) usually discard their needles after three years, and red
pine (Pinus resinosa) after four.
Some needles are discarded every year, but a tree may sometimes lose more needles in dry years, when it is stressed by drought. A large fall of old needles this autumn may also mean therewas an especially large crop of new needles a few years ago
Yew(Taxus) needles turn yellowand drop in late spring or early summer of their third year. Arborvitae (Thuja) sheds small fan-shaped branchlets, rather than individual needles.
“As long as your tree is only losing older needles, it’s normal,” Yiesla said.
On any branch, the needles or branchlets closest to the trunk are the oldest. Needle browning is only a sign of trouble if it’s happening anywhere else.
“If needles are turning brown and dropping all over the plant, itmay be stressed by drought, which is causing the needles to dry out,” Yiesla said. “That often happens on newly planted evergreens that haven’t been watered often enough.”
When an entire pine tree turns brown, it may be a sign of disease, such as pine wilt. Needles that turn brown in patches along a pine tree’s branches may be a sign of certain fungus diseases;
Austrian pine and Scots pine are especially susceptible. Certain fungal diseases can also cause a spruce to lose needles fromthe bottom up.
A single brown branch or a large brown patch on any evergreen may indicate winter damage or an insect infestation.
“Because brown needles can. be a symptom of so many different things, you should always seek expert help to get a firm diagnosis before you attempt any treatment,” Yiesla said. The Arboretum’s Plant Clinic can help find the source of the problem.
Most often, however, there is no problem. “As long as your tree is just losing older needles in the middle on a regular basis, it’s going through its normal pattern of growth and renewal,” she said. “There’s no reason to be concerned.”
The needles that fall to the ground will do what they’ve always done— create a layer of nourishing, insulating needles over the tree’s roots, like the floor of a pineywoods.
For tree and plant advice, contact the Plant Clinic at TheMortonArboretum (mortonarb.org/plantad vice or plantclinic@mor tonarb.org). Beth Botts is a staff writer at theArboretum.