Tree Care Diary – December

Tree Crowns in Wintertime


Can’t I just stay inside where it’s nice and warm?

Well yes of-course. In fact, trees have survived millions of winters and are generally well-adapted to cooler winter conditions. Much is happening underneath the tree bark right now to ensure your trees preserve their energy for the growth spurt next spring and protect themselves during the harsher climate of winter. However, that pretty ornamental tree you bought from the nursery or that perfect shade tree may be growing on the raggedy edge of their hardiness zones. And most newly planted trees will benefit from some love and attention in your yard this December.

Our advice embraces both physics and sustainable organic solutions. We take into account what trees are already doing to protect themselves and what wildlife does in your yard in winter. By reinforcing helpful animal behaviors and reducing some negative ones, your trees stand a better chance of surviving this harshest of seasons.

Your tree has 5 main survival objectives in winter:

i). to reduce metabolic rates
ii). to preserve energy in the form of carbohydrates (sugars) gained from photosynthesis during summer and early fall.
iii). to increase water uptake
iv). to prepare for the growing season in Spring (bud production)
v). to protect against damage caused by the harsher and colder winter climate

What are the trees doing to look after themselves in winter?

Right now, in early December, your trees are moving fluids around, adjusting levels of metabolites, hormones, proline and lipids to achieve the 5 aims above. Their success will determine the health, growth rate and fruit production of the tree in the summer growing season. They even have their own version of antifreeze. And when the temperature drops even lower, trees have mechanisms to ensure that dangerous ice crystals do minimal damage to the tree’s living tissues.

What you can do to help?

Our advice for tree care this winter is necessarily generic to thousands of tree species across many different habitats, elevations, temperatures and soil conditions across USA.

So your job is to make it personal. Get to know your trees in your garden. What species are they? What care do they need at this time of year, if any? What is the condition of the trunk, branches, roots etc? Walk around them and look at them. Do you see any problems? Are there broken branches? Is the tree weeping or oozing fluids? Are there any holes small or large? Your observations will determine what’s best for your tree. Share what you see with your local arborist or with us at Tree Top Pros. We’ll advise you if action is required or if it’s best to leave well alone. There are also things that only we can see, soil tests we can conduct and invisible cavities we can detect.

Why bother?

Your trees are valuable to you aesthetically. Matures trees in good condition add up to $10,000 to the financial value of your home due to their landscape appeal. They make your community a better place to live. They host local wildlife and are very good for the wider environment we all share. Your trees are worth looking after this winter.

So mindful of your trees’ top 5 priorities, we shall focus on things you can do in your own yard. Most of your winter attention will go towards trees less than 3 years old or newly planted specimens.

Our best 11 tree care tips for the month of December

1. WATER  – Give your trees a drink. Droughts in winter can deny trees the water they seek at this time of the year. So occasional watering during the winter on young trees, in particular, is recommended. However, only irrigate your trees when soil and trees are cool – not frozen. Before any watering, use your finger and wiggle it around in the soil at the base of your tree. If there’s moisture there already, you can avoid additional watering. Be aware that waterlogged tree roots can drown the tree and kill it.

2. MULCH – If the ground isn’t already frozen, you can add a 3 inch layer of organic mulch around your tree. This will help retain water in the cold dry winds and reduce stress on the tree’s roots from temperature extremes. We covered mulching in our November Tree Care Diary but it’s not too late to do it in December assuming your yard is ice-free. Keep the mulch away from the tree’s root flare at grade otherwise you’ll do more harm than good.

3. PROTECT YOUR TREES FROM TREE PESTS – Insects that over-winter on trees can be killed by severe frosts and ice. But many survive. Begin preventive applications for leaf diseases. Apply dormant oil applications to limit pests during the growing season. Try and use only organic, bio-degradable products which cause less harm to bees and other important pollinators.

Better still, invite more birds into your yard. Birds have a voracious appetite for caterpillars, beetle larvae/ pupae and termites that prey on your trees so you’ll need them around in the spring and summer. Start now in winter by bribing them with nesting cover and bird-boxes, bird food, fat balls and a bird bath too.

This more detailed article from the Wildlife Farm Alliance says that: “The overwhelming majority of songbirds are beneficial during nesting season because they feed pest insects to their hungry nestlings.”


Birds love moving water so install a small fountain for them too if you can stretch to it. As your yard becomes a haven for birds, they will reward you in spring and summer by scouring your trees for bugs when pests explode in numbers.

Feed the birds this winter
Feed birds in your yard this winter…

…and they will eat the tree pests next Spring and Summer

Attracting birds into your yard also works if you have fruit trees.


The trick for you is to enhance your yard habitat for birds that eat pests whilst making it less attractive for those birds that are likely to become pests themselves when fruits appear.

4. PRUNING – If your trees are small (less than 30 feet high), only trim away dead, broken or damaged branches in December. Leave structural pruning until late January or February.

And if you have oak trees or elms and they need attention, call your local arborist now for an appointment before the end of February. These species must only be pruned in the winter months of December, January and February. Note that some arborists get booked up early for large trees.

Back to your small trees, do not prune them if it means climbing a ladder; it’s just too dangerous. Working at elevation is always best left to the professionals. Improper tools or lack of tree knowledge can and does lead to deadly accidents. The Tree Care Industry of America (TCIA) reported more 211 casualties from tree-related incidents in 2018. Of these, 119 were deaths, most of whom were civilians. The best bet is to call in a professional arborist for the big jobs.

5. PROTECT FROM SUN – Protect those young trees you planted in fall. The sun on those bright cloudless days in winter will scald those exposed, young whips with thin bark. In bad cases, the sun will split and peel the bark of the young tree. This allows in pests and infection into the living structures beneath the bark. Use burlap to wrap the main stem from top to bottom. Remove the wrap in the Spring when leaves begin to shield the young tree’s trunk and branches from the sun’s rays.

6. PROTECT FROM BEING EATEN – Again we’re talking about protecting:

i). young whips/ saplings planted in the fall this year and the year before; and
ii) evergreen trees such as Green Arborvitae

Realize that they are both now food for deer, rabbits and mice. Deer damage alone now amounts to $2 billion every year, nationally. Deer can also attack pets and introduce disease-bearing ticks to your yard. Protect your trees by installing a simple flexible tree guard around each one. Biodegradable guards are better for the environment but plastic guards will do the job equally well.

Metal cloth (a type of wire mesh) can also be used. Ensure none of the tree guards you use come into contact with the tree at any point. Place 3 wooden or cane stakes around the young tree. Then wrap and secure the metal cloth around the stakes so it forms a protective triangle against bark nibblers.

You could also try applying deer and rabbit repellent to your trees. Make sure that any products you buy do no harm to pets and to the environment. Note that the repellents are best sprayed by a professional.
Remove the tree guards in spring. There’s much less danger from deer and rabbits when their more usual food sources return in abundance in springtime.

7. PROTECT FROM SALT and ICE MELTING PRODUCTS – Avoid dispensing rock salt or ice melts anywhere near your trees. Also avoid using large quantities on any sidewalks and parking areas in close proximity to trees or other landscape plants. This is because the sodium chloride in rock salt dehydrates the tree’s roots, needles and buds through osmotic action. If a mistake is made with rock salt, remove any visible salt from the base of the tree out to its drip line. Then water your tree to flush out the salt from the soil.
Keep large snow piles away from tree roots as much as possible as these will contain salt spray from road applications. If unavoidable, treat with fresh water after the piles have melted.

In future, opt for magnesium chloride-based melts instead. These are much better for your trees.

8. PROTECT AGAINST DESICCATION – Relative humidity halves approximately for every 20ºF drop in air temperature. This means that cold air can hold a lot less moisture than warm air. As a result, cold dry winds in winter can cause ‘winter burn’ damage to broadleaf evergreen trees such as rhododendrons, yew trees, boxwood and hollies. The damage is exacerbated if the soil is frozen as this compromises the tree’s ability to replace lost moisture from leaves from its roots.

Therefore, in late December consider spraying such trees with an anti-desiccant compound. Such materials form a barrier over leaf pores. This reduces water loss through transpiration yet is thin enough to allow the evergreen leaf to continue to breath.

The anti-desiccant works best if applied in late December and again late January. Again, choose products that are both biodegradable and organic. As a rule, anti-desiccants usually only work if sprayed within a specific temperature ‘window’ and if it doesn’t rain before drying.

9. PROTECT CITRUS TREES AGAINST FROST DAMAGE – Many varieties of citrus trees are vulnerable to frosts that creep into even the most southerly states some years. Much tree research in this area has been done as citrus groves are commercially important crops in states like Florida and California.

For home-owners, the advice is straightforward. If a freeze is expected, irrigate your citrus tree the day before. Water has a much higher heat capacity than dry soil. So moist soil is able to retain heat for longer and radiate it back to the tree at night when frost risk is highest.
Also rake back any mulch as soon as you hear of a high risk of frost in your area. Mulch will act as an insulator lowering the temperature of the tree at night. Removing the mulch allows the soil to warm the tree.

Additional pro-active steps are needed when sharp frosts are forecast. Wrap the central leader and other main branches of your citrus tree in layers of cloth from top to bottom. Take special care to protect the area on the trunk where the tree was grafted onto the root stock. As soon as frosts abate and warmth returns, remove the cloth.

10. PROTECT FROM SNOW DAMAGE – Multi-stemmed evergreen trees such as Juniper, Yew and Green Arborvitae are particularly susceptible to damage from heavy snowfall, says the University of Minnesota.
The remedy is simply to tie the main central branches together with any flexible and biodegradable material such as hemp twine. Remember to remove in the Spring otherwise it could damage the tree bark and lead to trunk deformities and restricted growth.

Where you see other trees suffer from heavy accumulations of snow, gently use a broom to brush the snow off with an upward sweep. Brushing downwards or shaking branches may cause them to snap off.

tree after ice storm

11. PROTECT YOUR TREES FROM ICE STORMS – Protection is not really possible because usually the whole tree is affected. Also, tree branches covered in hard ice are relatively brittle. So trying to shake ice off a tree limb could lead to the branch breaking/causing hidden damage. Tree branches flex and a sudden reduction of weight when ice is knocked off may cause damage to the tree’s vascular structures.

If the ice storm is bad and you notice some boughs are damaged, remove them with proper pruning techniques as soon as conditions allow. In most cases, the shape of the tree will return once the ice melts.
Cabling and bracing trees and their large branches are a way of reducing damage from expected, severe storms. This is specialist work only performed by trained arborists.

Please see our Tree Care Diary Disclaimer here. Despite our best efforts, our tree care advice cannot be applied ubiquitously for all regions and locations in the USA due to latitude, longitude and elevation differences. In case of doubt, always seek advice from your local certified arborist.

Tree Care Diary - May
Tree Care Diary - November