December garden tasks: Midwest

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Snow, ice and evergreens

Heavy, wet snow and ice storms cause most of the winter damage to Midwest trees and shrubs. Per Iowa State Extension:

• Brush soft snow off evergreens and multi-stem shrubs with a broom, sweeping upward from underneath so branches are not forced down further.
• Leave ice-coated branches alone. They are brittle, and knocking ice off breaks them. Let it melt.
• Arborvitae and junipers that splay open under snow often spring back once the snow melts. Iowa State suggests waiting until spring to judge the damage, then tying stems together loosely if needed.
• Before the next storm, loosely tie upright multi-stem evergreens with soft twine or strips of cloth.
• Leave large broken limbs, especially near power lines, to a certified arborist. Small broken branches can be cut cleanly back to a side branch or the trunk collar now.

If the ground has not frozen and December is dry, which sometimes happens in zone 6, give evergreens one more deep watering. Once the soil is frozen, stop.

Finish winter mulching (zones 5–6)

In zones 3–4, winter mulch usually went on in November. In zones 5–6, the ground often does not freeze for good until December, which makes this the month to finish. As the November guide explains, the mulch is there to keep frozen soil frozen, not to keep plants warm. Per Iowa State Extension, apply it after the soil has frozen.

• Spread several inches of straw, shredded leaves or evergreen boughs over perennial crowns, especially plants set out or divided this year.
• Cover strawberry rows with clean straw if you have not yet.
• Mound soil over grafted roses, then add straw on top once the mound freezes.
• Keep mulch pulled back from tree trunks so voles cannot hide while they feed on bark.

Winters with little snow are the hardest on perennials in the Midwest. Snow is the best insulation, so in an open, snowless December, mulch matters more than usual. See winter protection for perennials.

Keep salt out of the beds

Per UW–Madison Extension, salt damages plants in two ways. Spray from plows and traffic browns evergreen needles on the side facing the road. Salty meltwater draining into beds dehydrates roots and damages soil structure, and the injury often does not show until the following summer.

• Shovel before you salt, and use only as much deicer as you need to break the bond between ice and pavement.
• Use sand or grit for traction on walks next to planting beds. Illinois Extension has advice on gentler deicing practices.
• Do not pile salty snow from driveways and walks onto beds or around tree trunks.
• Put up burlap screens between busy roads and salt-sensitive plants such as white pine, spruce and yews.
• In spring, deep watering once beds thaw helps flush salt below the root zone.

Prune oaks now, and little else

Oak wilt is a serious disease across much of the Midwest. It spreads when sap beetles carry fungal spores to fresh wounds on oaks during the growing season. Per UMN Extension and the Minnesota DNR, do not prune or wound oaks from April through July. Michigan State University Extension recommends winter pruning for oaks. That makes December through March the safe window. If an oak is wounded during the risky months, cover the wound with paint or wound dressing right away. Oaks are the exception to the general advice against wound dressings.

For most other trees and shrubs, late winter is better than December. The March guide covers dormant pruning of fruit trees and summer-flowering shrubs. Per Iowa State Extension, prune spring-flowering shrubs such as lilac, forsythia and spring spirea right after they bloom, not in winter.

Fine to do now: remove dead, broken or storm-damaged branches, and cut evergreen boughs for decorating from the back of the plant.

Rabbits, voles and deer

As snow deepens, rabbits feed higher on trunks and shrubs, standing on the snowpack. Per Iowa State Extension, hardware-cloth and chicken-wire guards are the dependable fix:

• After each big snow, check that trunk guards still stick up well above the snow surface.
• Packing snow down around young trees after a storm makes it harder for voles to tunnel to the bark.
• Look for fresh gnawing on burning bush, serviceberry, apple, crabapple and roses, and add guards where you find it.
• Where deer pressure is high, keep netting on yews and arborvitae and reapply repellents during mild spells.

The Christmas tree

A fresh-cut tree that never runs out of water stays green through the holidays. Illinois Extension and Michigan State University Extension (Michigan is a leading Christmas tree state) agree on the basics:

• Pick a fresh tree. Needles should bend rather than snap, and few should drop when you shake a branch.
• Just before setting it up, cut a thin disk off the base of the trunk. Sap seals an old cut and blocks water uptake.
• Use a stand that holds plenty of water and check it every day, especially in the first week, when a fresh tree drinks heavily.
• Plain water is all it needs.
• Keep the tree away from heat vents, fireplaces and space heaters.

Afterward, cut off the boughs and lay them over perennial beds as winter mulch. Many Midwest cities collect trees for chipping.

Holiday plants and forced bulbs

Poinsettias: give them bright, indirect light and normal room temperature, away from drafts and heat vents. Water when the soil surface feels dry, and do not let the pot sit in a foil sleeve full of water. On the way home from the store, wrap the plant well. Even a short exposure to Midwest December air damages the leaves.

Amaryllis and Christmas cactus: per Illinois Extension, after blooming, cut off the amaryllis flower stalk and keep the leaves growing in a sunny window to rebuild the bulb. Keep Christmas cactus out of drafts, and do not move it while it is in bud.

Forcing hardy bulbs: per UMN Extension, tulips, daffodils, hyacinths and crocus need a long cold period, roughly 12 weeks or more, at cool temperatures above freezing before they will bloom indoors. Bulbs potted in early December and kept in a refrigerator or cold, frost-free garage bloom in March. Paperwhites and amaryllis do not need a cold period.

Planning

• Write down which vegetable varieties did well, where pests and diseases hit, and what grew where, so you can rotate tomato-family, squash-family and cabbage-family crops next year.
• Check stored dahlias, cannas and gladiolus monthly. Remove anything soft or moldy.
• Check stored squash, onions and potatoes the same way.
• Leave seed heads standing for winter birds, and keep feeders and a source of water going.

Common mistakes

Frequently asked

Can I prune trees in December in the Midwest?

Oaks, yes. Winter is the recommended time because of oak wilt. Dead or broken branches on any tree can come off now. For most other structural pruning, including fruit trees, wait until late winter (February–March), when the coldest weather is past and wounds close sooner.

Should I remove snow from my shrubs?

Brush off heavy, wet snow gently, sweeping upward from below, especially on evergreens and multi-stem shrubs. Dry, fluffy snow is good insulation and can stay. Leave ice alone.

How long does a fresh Christmas tree last?

A freshly cut tree kept continuously in water usually stays in good shape through the holiday season. The usual cause of early needle drop is a stand that went dry long enough for the cut to seal.

Can I put wood ashes from the fireplace on the garden?

Wood ash raises soil pH much like lime. Use it only if a soil test shows acidic soil, and spread it thinly. Where soil is already neutral to alkaline, as is common in parts of the Midwest, ash makes it more so.

Sources

1. How to Prevent Ice and Snow Damage on Trees and Shrubs, Iowa State University Extension
2. Winter Salt Injury and Salt-Tolerant Landscape Plants, University of Wisconsin–Madison Extension
3. Oak Wilt in Minnesota, University of Minnesota Extension
4. Prune Oaks in Winter to Avoid Oak Wilt, Michigan State University Extension
5. How to Protect Trees and Shrubs from Animal Damage Over Winter, Iowa State University Extension
6. Three Steps to a Long-Lasting Live Christmas Tree, University of Illinois Extension
7. Gift of Growth: Nurturing Your Holiday Plants, University of Illinois Extension
8. Growing Bulbs Indoors, University of Minnesota Extension

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