By: Teo Spengler
Deciduous trees drop their leaves in winter, but when do conifers shed needles? Conifers are a type of evergreen, but that doesn’t mean they are forever green. About the same time as deciduous tree leaves turn colors and fall, you’ll also see your favorite conifer dropping some needles. Read on for information on when and why conifers drop needles.
A conifer that sheds its needles may cause you to panic and ask: “Why is my conifer shedding needles?” But there is no need. A conifer shedding needles is completely natural.
Conifer needles do not last forever. The natural, annual needle shed allows your tree to get rid of the older needles to make room for new growth.
When do conifers shed needles? Do conifers shed their needles frequently? Generally, a conifer that sheds its needles will do so once a year, in autumn.
Every September through October, you’ll see your conifer shedding needles as part of its natural needle drop. First, the older, inner foliage yellows. Soon after, it falls to the ground. But the tree is not about to defoliate. On most conifers, new foliage stays green and does not fall.
All conifers do not shed the same number of needles. Some shed more, some less, some all needles, every year. And stress factors like drought and root damage can cause more needles to fall than usual.
White pine is a conifer that sheds its needles dramatically. It drops all needles except those from the current year and sometimes the prior year. These trees can look sparse by winter. On the other hand, a spruce is a conifer that sheds its needles inconspicuously. It retains up to five years of needles. That’s why you may not even notice the natural needle loss.
A few conifers are actually deciduous and drop all of their needles every year. Larch is a conifer that sheds its needles completely in the fall. Dawn redwood is another conifer shedding needles every year to pass the winter with bare branches.
If the needles on conifers in your backyard yellow and fall frequently—that is, at times other than fall—your tree may need help. Natural needle drop occurs in fall, but diseases or insects that attack conifers can also cause needle death.
Some types of woolly aphids cause needles to die and drop. Fungi-based diseases can also cause needle loss. The fungi generally attacks the conifers in spring and kills needles in the lower part of the tree. Fungal leaf spots and spider mites can kill conifer needles too. Additionally, heat and water stress can cause needles to die.
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Despite being called evergreen, the needles on evergreen trees don't stay green forever. The label "evergreen" refers to the trees' habit of not dropping their leaves, or needles, before winter the way deciduous trees do. But while evergreens are never totally without needles, they do regularly shed older needles as newer needles fill in. Some diseases and pests can harm evergreen needles, causing them to yellow and drop. But if it's the older inside needles that are yellowing and dropping, it's probably the normal fall needle drop, sometimes referred to as seasonal needle drop.
Softwood or coniferous trees can be harmed or killed by disease-causing organisms called pathogens. The most common tree diseases are caused by fungi, though some diseases are caused by bacteria or viruses. Fungi lack chlorophyll and derive nourishment by feeding on (parasitizing) trees. Many fungi are microscopic but some are visible in the form of mushrooms or conks. Other factors affecting tree disease include climate and where the tree or trees are planted.
Not all parts of a tree may be affected or exhibit symptoms. Disease may strike the needles, stem, trunk, roots, or some combination thereof. In some instances, trees can be saved by applying pesticides, trimming the diseased portions, or removing neighboring trees to provide more room. In other cases, the only solution is to remove the tree entirely.
Vicky advises you to check how fast a conifer grows and what its eventual height will be. Many only grow a few centimetres a year. And dwarf varieties will remain dwarf.
Conifers are generally easy care, but they prefer acid or neutral soil.
Fergus Garrett told us that he had started experimenting by using conifers in pots, mainly outside the front door of Great Dixter. So if your soil is very alkaline, you can put the conifers in pots with ericaceous compost.
I think I counted five different species of conifer in this grouping of pots at Great Dixter, although they’re not all in this photograph.
In both cases, the trees can look eerily similar. Luckily, there are two ways you can determine once and for all if your tree needs more or less water.
Precise-as-can-be check: Below your tree, dig 6-8 inches deep and grab a handful of soil. Your soil should be cool and moist. If it’s sopping wet, you’re overwatering. If your soil isn’t drenched or sandy, roll into a ball. If it crumbles, your tree needs more water. Poke the soil ball a few times. If it doesn’t budge, you probably have clay soil.
If your tree has too much water, it’s struggling to breathe. That excess water commandeers spots air pockets previously held. So, your tree roots are getting too much water and not enough oxygen. That’s a double whammy that could lead to root rot, fungi or long-term tree stress.
Fix. If you have clay soil, mix in compost to help it drain better.
Inspect. After it rains, see if there’s water pooling around your tree and find out where it’s coming from. Is water running downhill and landing at your tree’s base? Does your rain spout empty right near your tree? If you spot an environmental cause like this, it may be best to move the tree entirely.
Conifers, commonly referred to as “evergreens,” don’t regain needles permanently. In our Lake States region, most species lose their older needles every fall giving the trees a somewhat unhealthy appearance which should be no cause for concern.
Although referred to by many people as “evergreens,” trees with needle-shaped leaves are better identified as a “conifers.” This conifer classification includes tree families such as pine, spruce, fir, hemlock, cedar and others. Most of the tree species within these groups retain their needles to remain green year-round.
However, all conifers loose at least some of their needles every year. Most retain needles through several growing seasons but shed some of their older, less efficient, needles each fall. Prior to shedding these needles change color from their healthy green to yellow, orange and brownish-red depending on the species. Early in the shedding process, while the needles are still attached to the branches, these trees may have an unhealthy appearance which can cause unnecessary concern. Fortunately, needles lost in the fall from healthy trees should be replaced by new growth the following spring.
A good growing season followed by a few more moderate growing years will cause a greater percentage of the needles to be shed in some fall seasons than others, but is still no cause for alarm.
The larch family group of conifers, which includes the Michigan native tamarack (Larix laricina) species, are an exception to other conifers. This family of trees is fully deciduous, meaning they lose all of their needles every fall. Bare-branched all winter, they green up the following spring.
If whole trees or entire sections of conifer trees – other than larches – have needles changing color, this may be cause for concern. In contrast, needles at the base of the branches near the trunk changing color and falling off in the fall is just part of a natural process and should not be of concern with regards to tree health.
For additional information on how trees adapt to our area’s winter conditions visit the Michigan Forests Forever Teachers Guide.
This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).
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Tamarack trees are unusual conifers in that they shed all their needles each fall after turning a bright copper color.
People often call me asking why their pine tree is dying. The first question I always ask is whether all the needles are turning brown and falling off, or just the needles on the inside of the tree.
Pine trees and most other conifers are certainly defined as evergreen, but this does not mean the needles last forever. Here I will explain some basic differences between your maple and your pine.
“Broadleaf” and “conifer” are two terms used to describe tree leaves. Every tree fits loosely into one of these two categories. Broadleafed trees, such as maple and oak, have wide, flat leaves. Conifers, such as spruce and pine, have narrow, long needles. These are two different strategies at accomplishing the same task — photosynthesis.
Without going into advanced botany, here’s how they work:
— Needles give conifers an advantage on nutrient-poor growing sites and in cold, windy climates such as the Rocky Mountains.
— Large, flat leaves give broadleaf trees an advantage in nutrient-rich, hot climates such as the rainforest.
There exists an abundance of climates between those two examples where both types may thrive, including northern Indiana, which is relatively nutrient-rich but has cold winters and well-defined seasons.
Here in the northern U.S., all native broadleaf trees such as maples are deciduous, which means their leaf drop is influenced by the shortening of daylight hours and cooling daily temperatures and occurs on an annual, predictable basis. However, in the southern U.S., many varieties of broadleafed trees are evergreen, such as rhododendron and live oak, and do not shed their leaves for winter, just as most conifers do not. So, not all broadleaf trees are deciduous.
Most conifers such as pine, spruce, fir and cedar are evergreen, which means their needles (needles are a type of leaf) do not all drop at once, but rather are shed as the new season’s growth takes over responsibility for photosynthesis. This trait varies between species and is influenced by environmental factors, but when you look at any pine or spruce, you are usually seeing the needles produced only in the last 3 to 5 years. All the needles produced before that time have been shed as they age, wear down from the elements, become inefficient or are shaded out by the tree itself.
An exception among conifers present in northern Indiana would be the the tamarack, which loses its needles each fall after turning a beautifully bright copper color.
Both needles and broadleafs have advantages and disadvantages. Most yards have that certain spot where you just can’t seem to keep your favorite type of tree alive. Consider planting the opposite and you may find it thrives. We are fortunate to live in a climate that allows for a unique diversity of trees.
KEITH O’HERRIN is the City Forester for the City of LaPorte. He can be found at the Park and Recreation Office at 250 Pine Lake Ave. or reached at 326-9600.