The average person sheds 100 hairs a day. Cat and dogs’ shedding is stimulated by the light changes occurring around the equinoxes.
Trees also shed. We understand deciduous leaves turning color as the light wanes and falling from the tree with the first frost. What is less understood is evergreen needle cast, or shedding of the two- or three-year-old needles from the branches.
Master Gardeners get calls from concerned homeowners who say, “My tree looks ratty,” “My arborvitae (or substitute cedar, pine or fir tree) is dying from the inside out,” or “What can I spray on my tree to prevent it from dying?”
All evergreen lose needles, and some trees are just more obvious about it, which is what promotes the concerned calls. It is a natural process, and in the same way that the change of light stimulates our pets’ shedding, the lower light stimulates needle cast. You will notice it in late August. Longer needle pine trees such as Scots pine, Austrian pine or white pine create the most dramatic die back.
The older needles closest to the trunk die. Their photosynthesis job is completed. The newer needles have shaded out the older needles. Generally between one-quarter and one-third of the needles on a branch are shed. The shedding starts at the top of the tree and moves down to the bottom branches over several weeks or months. In drought years, more needles may be cast off. The needles go through a color change sequence from green, to red, brown, yellow and, finally, tan during this natural process.
Remember that the deciduous “evergreens,” the larch and dawn redwood trees, lose all their needles every year.
As a child, did you ever have a secret hideaway inside the longer, pendulous branches of a large cedar or pine tree? Space for a secret fort had been created over the years as the branches elongated and inside needles and small branches were sloughed off.
This is all reassuring, yes? But what if the needles at the tips of the branches turn brown and become brittle? This is not needle cast. Most likely, some type of environmental stress is causing the damage.
Environmental stressors can be:
♦ Excess heat because of temperature extremes or because of reflection from asphalt or other hard, dark surfaces.
♦ Insect infestation or fungal disease can cause branches tips to die. There are specific times of the year when these pests can be dealt with.
Man-caused problems can be:
♦ Drought because a drip watering system does not provide sufficient water for the extensive, spread-out root system.
♦ Tip damage caused by either over-spraying herbicide or heat-volatized herbicide.
♦ Uptake by the roots of pre-emergent herbicides such as Casaron.
♦ Root injury created by trenching or construction. This can cause significant needle dieback.
♦ Root injury caused by compaction. Parking vehicles on the lawn under the shade of a tree compacts the soil and kills roots. Compaction also prevents water penetration into the soil, so the roots suffer drought.
Want a better idea of what could it be? You can bring samples to the WSU Master Gardener clinic for an accurate diagnosis. Clinics take place Monday and Wednesday from 1 to 4 p.m. at 400 Washington St. in Wenatchee.
A WSU Master Gardeners of Chelan County column appears weekly in the At Home section. Bonnie Orr is one of four columnists featured.