A tree without leaves

How Do Trees Know When to Wake Up?

Illustration by Adelaide Tyrol

We take for granted that trees drop their leaves in fall and open their buds in spring, with a glorious burst of flowers and leaves. Indeed, florists know that apple branches cut in March and brought inside will flower in a vase in just a few weeks. Yet if you were to cut branches from the same tree in November and bring them indoors, they would never sprout. What accounts for the difference?

Trees survive sub-freezing winters by becoming dormant, a gradual process that begins long before winter. As summer gives way to autumn, cooling temperatures and lengthening nights tell trees to stop elongating their twigs and make resting buds instead. As growth slows, so does chlorophyll production, and leaves begin to change color. A layer of cork starts to form across the base of the leaf stem, cutting off nutrients and eventually causing the leaf to drop.

Lack of growth and dying leaves however, do not mean that a tree is truly winterized. Trees, or their cut branches, may still be roused into sprouting in early fall, as they are only in a state of pre-dormancy. This condition is a general response to environmental stress. In other words, pre-dormancy is brought on not just by lengthening nights but also by some other stress, like drought. Those occasional trees that we notice turning color and dropping their leaves in midsummer are stressed. They are shutting down their metabolic activity, but in this pre-dormant state, they would still recommence growth if conditions again became favorable.

However, in temperate zones, the onset of fall brings shortening days as well as cold, and together these signals send trees into the next phase of dormancy, called true dormancy, which begins a few weeks after growth cessation.

Trees sense day length (actually night length) through phytochrome, a blue pigment that exists in two interconvertible forms. Native phytochrome converts to ‘activated’ phytochrome when hit by a photon of red light. In the dark, the activated phytochrome reverts to the native form. The amount of time in the dark required for all the activated phytochrome to return to the native state is how plants measure the length of the night. Long nights lead to the production of abscisic acid, which inhibits bud growth, promotes cork formation at leaf bases, and stimulates the complex ‘hardening off’ process that transforms the delicate live tissues of trees into something that can withstand severe cold.

Once truly dormant in late fall, trees will not respond in any fashion to warm temperatures. Before becoming receptive to wake-up calls, a certain amount of time in the cold must first accrue. This is referred to as the number of chill hours. Extreme cold, however, is not necessary. Trees start racking up chill hours at 44 degrees F, and it is generally accepted that below 30 degrees F, chill hours don’t accumulate. It’s the time spent between 44 and 30 degrees F, generally through fall to midwinter, that counts. This hints at some yet-to-be-defined biological counting process that grinds to a halt once tissues and cells are below freezing.

During true dormancy, trees become progressively more resistant to freeze damage through cellular changes and accumulation of frost- and stress-protective compounds.
Like many insects and amphibians that also withstand our northern winters, trees evacuate water from their cells, turn starches into sugary antifreezes, add fatty acids to keep their cell membranes supple, and take advantage of pure water’s super-cooling properties to withstand temperatures far below where water would otherwise freeze.

While it is not known how trees ‘count’ their genetically programmed chill-hours, recent research shows that some genes, including those that protect cells from the stress of dehydration, remain active during dormancy. At the end of chill-hour accumulation, the activity of these genes decreases while other genes become active, producing, among other things, antioxidants and vitamin C. These compounds get rid of hydrogen peroxide, an oxidizing agent that builds up during true dormancy and would damage plant tissue it if were still around once the trees resumed growing.

In New Hampshire and Vermont, trees have typically accumulated their necessary chill hours by sometime in January, when changes in gene activity herald entry into the post-dormant phase. At this point, they are held in check by the cold, not the length of the day. And because the post-dormant phase includes the coldest part of the year (January and February), freeze resistance actually reaches its peak during post-dormancy, then declines gradually as the cold eases.

The arrival of warm temperatures in April, more than increased day length, induces trees to open their buds. Usually the timing is appropriate, though unseasonable early warmth can sometimes fool trees, as in the early opening of apple blossoms and oak and maple leaves in April and May of 2010. All three species suffered from a late frost in May.

Li Shen is an adjunct professor at the Dartmouth Medical School and a member of the Thetford conservation commission.

It really hasn’t been feeling – or looking – like spring lately.

Its hard to get into the spring spirit when most people have had to stay bundled up because of the cooler weather, we even had some snow and slush Monday.

There are some buds on some trees, but you’ll have to wait awhile until the blossoms and leaves come out. Trees usually begin to leaf the third week of April. That’s not the case this season, though – temperatures have been too consistently cool.

The warm spells that we have felt this month hasn’t been long enough for the plants, flowers, and trees to really bloom, and even for some people’s grass to turn green.

This season, we will begin to see trees flowering in late April, and into early May. Magnolia trees will begin to flower, and then the leaves will begin to pop on the maples and oaks.

Some trees here in the Pioneer Valley are beginning to show buds. Gary Courchesne from G&H Landscaping explained, “They are starting to. The buds are swelling and the seed pods are starting to drop off, and you’ll start seeing them in parking lots and driveways. The foliage will follow, we just need a little more heat.”

Warmer air looks to be coming this weekend and into next week – and likely more buds.

Where’s the green? Slowest start to spring in many years

WATCH ABOVE: The mosquito-like pest abound this season thanks to last year’s wet Summer and Fall. Peter Kim reports.

TORONTO – Do you remember looking out your window last May and seeing the blue skies and green leaves? How about this year?

If you’re like a lot of people, you’re likely tired of looking out your window at the brown, broken, and seemingly lifeless branches of trees that dot the streets. Though some buds are making a slow appearance, they seem to be taking their sweet time.

READ MORE: Weather challenge–Who had the worst winter in Canada?

Tom Hildebrand, a forester with Toronto and Region Conservation Authority said that it’s not as bad as it may seem.

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“We’re not really that far behind,” he told Global News. “Last year was exceptionally early, the last couple of springs have been early… We’re maybe a week behind what would be considered the normal for the last 10-15 years.”

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According to Environment Canada, the daily average temperature for Toronto in the month of April is 7.1. The past few years have indeed, been either close to average or significantly higher: in 2010 the daily mean temperature for the month of April was an incredible 10.5 C. In 2009, it was 7.8 and 2008, 9.5. From 2011 to 2013, it was closer to average. But this April it was a full degree colder. The last time that happened was 2007.

This spring has gotten off to a slow start, in part due to the long and cold winter we had.

“The trends that we saw from the winter to the first part of the spring, it’s just been a continuation,” Geoff Coulson, warning preparedness meteorologist with Environment Canada told Global News.

Coulson said he’s noticed the buds just starting to emerge on the trees. “There’s a beautiful cherry blossom tree…and those cherry blossoms are just finally starting to come out,” Coulson said. “They’re not out, but they’re starting.”

In Toronto’s High Park, the cherry blossom watch is in full swing. According to High Park Toronto‘s website, the blooms are still two weeks away. “Cold mornings and high winds don’t help out this spring.”

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Hildebrand said that, though the leaves aren’t out yet on the trees just yet, that’s close to normal for this time of year. Also, he stressed that the growth of trees isn’t really tied to temperature, but more to the length of the day.

Last year on May 1, there was at least some green on the trees. Nicole Mortillaro

The trees may also be dealing with the effects of the ice storm at the end of December. Though the trees wouldn’t have lost any of the stored energy they would need in the spring, the buds would typically be located at the top branches — the ones that were damaged. That wouldn’t be seen so much in forests, but more so in our backyards or on the streets.

“A slow spring is always better than an early one,” Hildebrand said. That’s because in an early spring the buds may begin to come out, but the insects aren’t around to pollinate them.

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Coulson said that temperatures are expected to continue to be a degree or so below normal.

As for what’s ahead, Coulson said that for now, forecasters are calling for more seasonal temperatures in July.

“Again, that’s a long look into the future, and things could change by then.”

© 2014 Shaw Media


The only life showing on this cherry tree is a leaf bud emerging from the trunk.

(Submitted photo)

Q: We have three 6-foot weeping cherries that we planted last year. Two are pink and one is white. The two pink trees grew, leafed and blossomed normally this year. The white one has no leaves… just small buds that are brittle and appear to be dead. The tree apparently is still alive though, because I can see small leaves coming off of the main trunk. Is there any hope for a comeback?

A: I’ve been seeing a fair amount of winter dieback like this lately on cherries, Japanese maples and other trees.

It’s a good sign that you’re seeing at least some buds pushing out of the trunk of the white-blooming cherry. However, it’s a bad sign that the buds in the branches are all apparently dead.

The question now is whether there’s enough life left that the tree will continue in recovery mode or just give up and die – possible when summer’s heat arrives.

If this were a person, your “patient” would be in the intensive care ward with a prognosis of “not out of the woods yet.”

The best scenario is that the winter damage was severe enough to kill off this year’s buds but not so much that it killed all of the branches. If that’s the case, you’ll see new leaf buds emerging from the branches in the next few weeks.

More likely is that the branches are dead and won’t push any new growth. You might get a feel for that now by bending a few branches to see if they’re still pliable and green inside (a good sign) or brittle enough that they snap and are brown throughout (a bad sign).

I’d wait at least a few more weeks to give the tree every chance for a comeback. But if June comes and goes and the branches are bare, all you can do is prune them off.

Then it’s a matter of seeing what’s left. You may find that all or most of the branches are dead, and that a few shoots emerging from the trunk are all you have left.

If that’s the case, it’s a judgment call of whether you let the poor emaciated thing try to grow back into some kind of semblance of a tree or just cut your losses now and replace it.

I usually lean toward mercy and patience, giving trees with a near-death experience a year or two to see which direction they’re heading.

There’s nothing you can spray or do to hasten the recovery. If the soil is lacking in nutrients (determined by a soil test), adding an appropriate fertilizer might do some good. But fertilizer isn’t medicine, and pumping a lot of fast-acting nitrogen around the base of it to “stimulate growth” may do more harm than good.

Term for the state of a deciduous tree during winter?

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KidZone ScienceTrees

© Contributed by Leanne Guenther

(note: Links to printables found at the bottom of this page)

Trees are an important part of our world. They provide wood for building and pulp for making paper. They provide habitats (homes) for all sorts of insects, birds and other animals. Many types of fruits and nuts come from trees — including apples, oranges, walnuts, pears and peaches. Even the sap of trees is useful as food for insects and for making maple syrup — yum!
Trees also help to keep our air clean and our ecosystems healthy. We breathe in oxygen and breathe out carbon dioxide. Trees breathe in carbon dioxide and breathe out oxygen. We’re perfect partners!
Trees do lots for us, our environment and other plants and animals in nature but we don’t just love trees for practical reasons. Trees can also be very beautiful — tall enough they seem to touch the sky and so big around you can’t even hug them. Thousands of artists, professional and amateur alike have painted pictures of trees and thousands of poems, songs and stories have been written about them. I would guess that just about everyone on earth has at some point in their life stopped to enjoy the beauty of a tree.

Types of Trees:

There are two main types of trees: deciduous and evergreen. Deciduous trees lose all of their leaves for part of the year. In cold climates, this happens during the autumn so that the trees are bare throughout the winter. In hot and dry climates, deciduous trees usually lose their leaves during the dry season.
Evergreen trees don’t lose all of their leaves at the same time — they always have some foliage. They do lose their leaves a little at a time with new ones growing in to replace the old but a healthy evergreen tree is never completely without leaves.

Parts of a Tree:


The roots are the part of the tree that grows underground. Trees have a lot of roots — the size of the root system is usually as big as the part of the tree above the ground. This is necessary because the roots help support the tree. It takes a lot of roots to hold up a 100 foot tree!

Besides keeping the tree from tipping over, the main job of the roots is to collect water and nutrients from the soil and to store them for times when there isn’t as much available.


The crown is made up of the leaves and branches at the top of a tree. The crown shades the roots, collects energy from the sun (photosynthesis) and allows the tree to remove extra water to keep it cool (transpiration — similar to sweating in animals). The crowns of trees come in many shapes and sizes!


Leaves are the part of the crown of a tree. They are the part of the tree that converts energy into food (sugar). Leaves are the food factories of a tree. They contain a very special substance called chlorophyll — it is chlorophyll that gives leaves their green colour. Chlorophyll is an extremely important biomolecule, used in photosynthesis — leaves use the sun’s energy to convert carbon dioxide from the atmosphere and water from the soil into sugar and oxygen. The sugar, which is the tree’s food, is either used or stored in the branches, trunk and roots. The oxygen is released back into the atmosphere.


The branches provide the support to distribute the leaves efficiently for the type of tree and the environment. They also serve as conduits for water and nutrients and as storage for extra sugar.


The trunk of the tree provides its shape and support and holds up the crown. The trunk transports water and nutrients from the soil and sugar from the leaves.

Parts of the Trunk:

Inside the trunk of a tree are a number of rings. Each year of the tree’s life a new ring is added so many people refer to them as the annual rings. The rings are actually made up of different parts:


The outside layer of the trunk, branches and twigs of trees. The bark serves as a protective layer for the more delicate inside wood of the tree. Trees actually have inner bark and outer bark — the inner layer of bark is made up of living cells and the outer layer is made of dead cells, sort of like our fingernails.

The scientific name for the inner layer of bark is Phloem. The main job of this inner layer is to carry sap full of sugar from the leaves to the rest of the tree.

A number of handy things are made from bark including latex, cinnamon and some kinds of poisons. Because bark is a protective layer for the tree, keeping it safe from insects and animals, it isn’t surprising the strong flavours, scents and toxins can often be found in the bark of different types of trees.


The thin layer of living cells just inside the bark is called cambium. It is the part of the tree that makes new cells allowing the tree to grow wider each year.

Sapwood (Xylem):

The scientific name for sapwood is xylem. It is made up of a network of living cells that bring water and nutrients up from the roots to the branches, twigs and leaves. It is the youngest wood of the tree — over the years, the inner layers of sapwood die and become heartwood.


The heartwood is dead sapwood in the center of the trunk. It is the hardest wood of the tree giving it support and strength. It is usually darker in colour than the sapwood.


Pith is the tiny dark spot of spongy living cells right in the center of the tree trunk. Essential nutrients are carried up through the pith. It’s placement right in the center means it is the most protected from damage by insects, the wind or animals.

Printable Activities and Worksheets from KidZone.ws:

  • Autumn Leaf Collection Book
  • Botanical Prints and Illustrations
  • Information About Trees:

Information About Trees – page 1
(color) or (B&W)
Information About Trees – page 2
(color) or (B&W)
Information About Trees – page 3
(color) or (B&W)

  • Parts of a Tree Worksheet:

Fill in the blanks:
Parts of a Tree Worksheet
(color) or (B&W)
Parts of a Tree Worksheet
(color) or (B&W)

  • Parts of a Trunk Worksheet

Fill in the blanks:
Parts of a Trunk Worksheet
(color) or (B&W)
Parts of a Trunk Worksheet
(color) or (B&W)

Links to Printable Activities and Worksheets from Other Websites:

  • Aesop’s Fable: The Plane Tree
  • Arbor Day Ideas
  • Parts of a Tree
  • Picture Clue Read and Trace Worksheets
  • Poetry:
    • The Beech Tree
    • Trees
    • What Do We Plant?
  • Tree and Leaf themed coloring pages
  • Tree and Leaf themed crafts
Check out the Spanish version of this section >

Why Does My Tree Only Have Leaves on One Side?

One of the best parts of summer? Relaxing beneath trees’ cool, shady canopy.

But if your tree has no leaves on one side, your favorite summer spot looks far less appealing. Even worse, your tree is likely suffering.

What could be causing the lack of leaves?

Our reader, Jim, recently asked this question. “Half of one of my maple trees has leaves. The other half looks like it started, but then there is nothing. Is this normal due to a long winter? Is there a problem, or is the tree dying?”

Like Jim, you may be wondering why your tree is growing this way. Below we explore causes and solutions for trees not leafing out.

Only half of my maple tree has leaves. Is this a sign of maple decline?

Reduced leaf growth is a sign of a declining maple tree.

Other symptoms of maple tree dieback include:

  • Reduced twig growth

  • Small, dead branches in the upper tree canopy in late spring or early summer

  • Dead, brittle or decaying roots

  • Fall colored maple leaves in July or August

Over time, larger and more visible dead branches will appear, causing crown dieback in maple trees.

What causes trees to only have leaves on one side?

Consider what your tree was exposed to before its lack of leaf growth: Harsh weather? Insufficient planting space? A nearby construction project?

If your pre-construction planning didn’t account for the safety of your trees, they could suffer. Construction damage can cause soil compaction and/or root damage to the tree.

Sparse leaves are also linked to abnormally cold winter temperatures and soil moisture. For example, frozen soil and frigid winds could cause one side of the tree to suffer more injury. A weakened tree is also more susceptible to diseases and pests.

Another cause of canopy thinning is girdling roots—which wrap around other roots or the tree’s trunk and cut off the flow of water and nutrients. When nutrient uptake is compromised, you’ll see the effects in the tree’s canopy.

What are the solutions for a tree that does not leaf out?

Be sure to treat your trees with water, fertilizer and pruning as part of their plant health care program.

Dig deeper into the best solution for your tree by requesting a tree inspection. Your local arborist will pinpoint the specific cause of tree decline and recommend treatment.

Deciduous Tree Leafing Problems: Why Won’t My Tree Leaf Out?

Deciduous trees are trees that lose their leaves at some point during the winter. These trees, especially fruit trees, require a period of dormancy brought about by colder temperatures in order to thrive. Deciduous tree leafing problems are common and can evoke anxiety in homeowners who become fearful that their favorite trees will not recover. Diagnosing trees not leafing out is not an easy task and one that follows a process of elimination.

Why Won’t My Tree Leaf Out?

Trees not leafing out? A tree with no leaves when spring comes indicates a tree in some degree of distress. It is best to do a thorough investigation before jumping to any conclusions regarding the lack of growth.

A tree with no leaves can be attributed to bud issues. If the tree has some leaves, begin your assessment of buds that never broke. If you cut into the bud and it is brown and dead, it is an indication that it has been dead quite a long time. If the bud is brown on the inside but still green on the outside, the damage is probably due to cold damage.

You can also check the branches to see if they are still alive. If there are many buds dead, but the branch is alive, then the tree has been suffering for some time. The problem could be due to stress or a root problem.

Suspect disease when there are no buds at all. Verticillium wilt, caused by a fungus, is common in maples and can be diagnosed if the wood is streaked. Unfortunately, there are no controls for this problem.

Some trees, like fruit trees, fail to leaf out simply because they did properly chill over the winter.

How to Get a Tree to Grow Leaves

How to get a tree to grow leaves is not a simple task and is typically dependent on the reason behind the leafing out problem. The best way to get a tree to grow leaves is to practice proper care and maintenance. Following a regular watering, feeding and pruning schedule will ensure that trees remain as healthy as possible.

Proper irrigation will sometimes help promote health in a tree that is suffering stress. Taking up grass and other vegetation around the tree also helps to reduce the competition for nutrients and is a profitable practice for keeping trees vital.

Some things, however, cannot be controlled, such as the weather.

Getting Professional Help for a Tree With No Leaves

If you have trees that have not leafed out, it is always best to seek the guidance of an expert before making any decisions on treatment. Check with your local Cooperative Extension Office for help with diagnosis and treatment for deciduous tree leafing problems.

Many things can lead to the death of a tree, including old age, insects, various diseases, and fungus. At A & E Tree, we know that for the most part, many trees live for decades or even centuries. However, if you are a Kansas City area homeowner who suspects a tree in your yard is not doing so well, there are a few ways to determine whether or not the tree is dead.

Trees are important for many reasons. Not only do they beautify your landscape and provide shade, they are also used in everything from buildings and wood floors to paper. The death of a flower, shrub, or other plant in your yard may not be as important as the death of a tree, that somehow seems sad and even alarming.

How long do trees typically live?

The life of a tree depends on the species in many cases. For instance, while an oak or pine tree may live for two or three hundred years, a maple tree often lives as long as a century. Ornamental trees usually have a shorter life span, living on average 15 to 20 years. When a tree is dying due to old age, there is little you can do about it.

Given the severe drought in some areas of the country and torrential rains/flooding in other areas, it is no wonder that many trees die. Just like other plants, trees need nourishment and water, but too much or too little water can be devastating.

When you suspect a tree in your yard is dead or on its way, there are a few things you can do to confirm your suspicions – or hopefully, learn that the tree may not be on it’s last “limb.”

A lack of leaves either on the entire tree, or a particular section. During spring and summer months, most trees are covered with healthy leaves. If your tree doesn’t produce leaves, or leaves are only present on a portion of the tree, it could be a sign that the tree is dying.

Another symptom of a dead tree is brittle bark or a lack of bark. When a tree starts losing its bark or has lost its bark, chances are the tree is dead.

Dying limbs are another indication a tree may be dead. If sizeable limbs appear dead or fall off of the tree, or the trunk becomes brittle/sponge-like in substance, it could indicate the tree is dead.

Your tree doesn’t produce buds or leaves in spring months. If the tree looks like a brittle piece of wood with no leaves coming out in spring or early summer months, there is little doubt it has lived out its lifespan. Another sign of a dead tree is a twig or limb that cracks when you break it off, with no green tissue inside the twig/limb. When you find only brown or tan pulp that’s dry and not softer green pulp in the middle, most likely the tree is beyond help.

If you do determine that a portion of the tree in your yard is dead, but other areas seem to be alive, the best thing you can do is to have the dead area pruned or trimmed away. Pruning away any dead portion of the tree helps relieve stress, and allows the portion that is still living to receive more nutrients. It also reduces the risk of insect infestation.

Suspect a tree in your eastern Kansas yard is dead, or on its death bed? Give A & E Tree a call today. Dead trees are not only unsightly, they can be a danger to your home and family as well!

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