By Marilyn Loser

2014 September 24

It’s officially fall and I’m thinking about what I need to do for my trees to help them with their transition to winter dormancy.  Going dormant is the way most temperate perennial plants (this include trees) survive the cold of winter. 

“You can compare dormancy to an extended period of "rest" for plants, when their metabolic processes, such as photosynthesis, respiration and transpiration slow down,” says Amanda Sears, a county extension agent in Virginia. “Most temperate perennial plants will enter dormancy in autumn as daylight shortens, temperatures (including soil temperatures) become cooler, terminal buds are set, and perhaps as a result of drier conditions during late summer and fall.”

Sears continues, “It is important that landscape maintenance activities not interfere with the plant's natural process of becoming dormant.” So what does this mean in Alamosa?

Mulch: For me, it means making sure my trees that are not planted in the lawn have a 4” layer of organic mulch.  I still like the shaggy bark mulch that doesn’t blow as easily as wood chips.  If the layer has been in place for some time, I make sure it is loose so moisture can seep through and not run off.

The two maple trees I planted this summer, a Tatarian (Acer tataricum ‘Hot Wings’) and an Autumn Blaze (Acer x freemanii - rubrum), are turning a beautiful red.  The roots of young trees are especially susceptible to the extreme temperature changes we witness daily during Alamosa winters. The mulch layer can help mitigate the rapid temperature changes as well as reduce the rate of soil water evaporation.

Tree wrap: One maple still has the protective cardboard tube around the trunk it came with.  I will wrap the other tree trunk with tree wrap up to the first branches.  This might give some temperature protection – like putting on a light sweater.  More importantly, the protective layer will help prevent winter sunscald on the southwest side of the tender trunk. Any winter wraps should be removed in the spring.  Leaving them on can encourage pest or disease damage.

Water: During fall, I water trees less, but I don’t want the soil to completely dry out. In fact, I’ve also been watering them during our recent winters that have been warm (for Alamosa!) and dry.  According to Jim Skiera, Executive Director of the International Society of Arboriculture, “Winter droughts require watering as much as summer droughts. If temperatures permit, an occasional watering during the winter on young trees can be a lifesaver. But be sure to water when soil and trees are cool but not frozen.”

And there are tree care practices to avoid in the fall.

Fertilizing: Most sources say to avoid fertilizing trees in the fall as this stimulates growth just when trees are trying to slow down. According to University of Minnesota Extension website, “Most trees experience a single flush of growth during spring followed by slower growth throughout the summer and fall.” Therefore, it’s a good idea to have nutrients available to the tree as this growth is about to occur. “The most beneficial time to apply fertilizer is from when the ground is workable in the spring until just before trees start growing in early May,” says the website. “On sandy soils, applications should be split, half in early spring and half in mid- to late May.”

Pruning: Some resources suggest that fall, after leaf drop, is a good time to prune trees.  I now agree with those that say you should wait until trees are more dormant to prune – say, January or February.

"As I try to stress every year at this time [fall], pruning them now stimulates new growth just when the plants are trying to go dormant, and this severely weakens the plants," says Mike McGrath, host of Philadelphia’s “You Bet Your Garden” radio show.

“Fall is considered a poor time to prune most woody perennials,” reports Sears. “Pruning will remove terminal buds (the bud at the end of stem) that help to maintain dormancy in many species. The presence of the terminal bud suppresses the growth of lower buds through a process called apical dominance. If you remove the terminal bud, it may encourage lateral buds to initiate growth in a plant that has not yet fully entered a dormant state. If this occurs, it will be hard for the plant to achieve dormancy, leaving the plant more prone to winter damage.”

“When I grow up I want to be a tree, Want to make my home with the birds and the bees… I’ll let my joints get stiff, put my feet in the ground, Take the winters off and settle down” by John Gorka in the song “Branching Out”