Often gardeners are worried when they see needles of their conifers turn yellow in the autumn and drop off the plant. After all, aren’t conifers supposed to be evergreen?
Well, sort of…
First, let’s eliminate from this discussion the conifers that lose all their needles in the fall and from which even beginning gardeners expect nothing less, a very small group that includes larches (Larix spp.), bald cypresses (Taxodium spp.) and the dawn redwood (Metasequoia glyptostroboides). The vast majority of other conifers are indeed “evergreen”.
However, conifers are evergreen in the sense that most keep enough needles through the winter that they seem fully covered, but even so, old needles do fall off throughout the year, mostly abundantly in the fall.
How long needles remain on the plant depends mostly on the species, although environmental conditions are also a factor. In some species, needles last 2 or 3 years, while they remain on the plant for 4 or 5 years in others. The bristlecone pine (Pinus longaeva) has the longest lasting needles: they can stay on the plant up to 45 years!
Usually old needles turn yellow first, then turn reddish brown before falling, but this varies by species. And since it is the older needles that drop off, that is those on the inside branches of the tree, the loss is partly hidden, so it’s not something you always notice.
But My Conifer is Losing More Needles Than Usual!
Before jumping to the conclusion that your conifer is dying, let’s look at the other possibilities. Here they are, more or less in order of probability:
- It’s losing a normal number of needles, but you simply never noticed it before. (Many people, possibly even most, are “plant blind”: they don’t much notice the plants around them unless they begin awakening to the nature that surrounds them.)
- Your conifer is one of those whose needle drop is naturally quite visible (the various white pines, like Pinus strobus, yellow much more noticeably than other pines in the fall).
- It produced more needles than normal 2 years ago (or 3, 4 or 5 years ago) and so when it’s time for the old needles from that year to drop, the sudden loss can be quite striking.
- It produced fewer needles than normal during the current year and therefore the needle drop is not as well hidden as it usually is.
- It recently suffered from some sort of stress. (Anything that increases the stress in a conifer, such as an exceptionally dry or hot summer, will lead to greater-than-usual needle loss.)
- It really does have a problem.
Even if you do believe your conifer really has a problem, generally there is not much you can or should do in the fall, other than watering if the soil is dry. Otherwise, it’s best to wait until spring to decide what should be done (insect- or disease-treatments, fertilizer application, correcting the soil pH, transplanting to a more suitable location, etc.).
And very often in the spring, even though you were sure you had pinned down the needle loss to something important the previous fall, you discover that, ultimately, when the new needles grow in, the plant really didn’t have a problem after all.
A simple tempest in a horticultural teapot!