How will this warm winter affect my plants?

How will this unusually warm winter affect my garden, lawn, trees and shrubs? Will pests be a bigger problem? Can I still prune my fruit trees?

Plant dormancy is affected by day length and temperature. Plants slowly start moving into dormancy in late summer, acclimating as seasons progress.

Acclimation is a physical and physiological process that protects plants through the winter. Though cold temperatures have some effect, dormancy is most influenced by longer nights (photoperiodism) and causes hormonal changes that prompt the plant to rest an appropriate length of time.

The length of dormancy depends on the plant species and the duration of low temperatures. It’s critical that the plants don’t de-acclimate too soon or they can experience cold damage. In general, dormancy is overcome when the buds of trees and shrubs experience 24° to 50° F for approximately 4 to 8 weeks at which time the plants break bud.

Garden

• Spring bulbs like tulips, daffodils and crocus are commonly seen emerging from the soil, especially on the south side of landscapes where the soil warms early in the season. These plants often emerge even when snow is on the ground. In the event cold weather returns, you may see a little cold damage on the leaves, but the plants won’t be harmed otherwise.
• Hardy perennials have been reported by some gardeners emerging from the soil even in December. Like the buds, you may see some cold damage on the leaf edges if temperatures drop, but the plant should survive.
• Because of the swings in temperatures, provide plants with extra care as we move into the growing season to reduce plant stress.
  • Mulch plant roots and water if the soil is dry.
  • Prune appropriately to encourage good form and to open up canopies to light and airflow. This will reduce the potential for insects to take up residence and for fungal leaf spot diseases to emerge.
• Keep good records of how the plants in your yard and garden tolerate these extreme temperatures. Because unpredictable, erratic weather conditions are likely to continue in the future, documentation of which species perform well with these weather patterns can be used to inform future plant selection for a more resilient landscape in the coming years.

Trees and shrubs

Which trees and shrubs are likely to be impacted by this weird winter?

It depends on the species and the genetic origin of the plant material (provenance).

• Some of our northern trees and shrubs are adapted to a lengthy winter period and are not easily tricked into waking up early with an unseasonable warm-up. Unfortunately, there is little documentation that helps gardeners know specifically which plants fall into this category because of the variables involved.
• The plant’s growing conditions also play a role. A microclimate such as a southern exposure foundation planting is likely to experience warmer local conditions than those with a northern exposure. The same plant species growing at each site may respond differently to the weather patterns. 
• The recent warm temperatures combined with longer day length triggered bud break on a few species, particularly those growing in protected microclimates. If temperatures remain above freezing, this tender new growth may survive. However, if night temperatures dip into the 20’s or less, and day and night temperatures fluctuate, the tender new growth will likely die.

Plant health going into winter

Plant health going into winter plays an important role in whether a tree or shrub is impacted by winter temperature changes.

• While we can’t do anything to prevent plants from “waking up” early, we can support the health of our plants throughout the year to help them survive challenging conditions associated with erratic weather and climatic trends.
  • If a plant is stressed by drought, disease, or other damage, it will struggle to recover from cold damage.
  • If it is healthy going into winter, then it will likely be able to initiate new growth from axillary side buds when temperatures become more consistent in spring. 

Lack of snow, lack of insulation

• Similar to mulch, snow helps to insulate tree and shrub roots from extreme swings in soil temperatures (freeze-thaw cycle).
• Without much snow, a layer of mulch can be applied with the added benefit of protecting the roots year-round. If you don’t have bark mulch readily available, a layer of leaves can do the trick. 

A good fence is the best defense

• Reduced snow cover exposes the branches at the base of the plants, making them easy for animals like rabbits and voles to browse, girdling stems and trunks.
• Protect trees and shrubs with adequate physical barriers like hardware cloth fencing around the base of your trees and shrubs to prevent animal browse. 

Should I be watering my tree if day temperatures are routinely warm?

• Do not water frozen soil.
• Start watering plants when the ground is completely thawed, your trees are actively growing, and especially if conditions are droughty.

Can I prune my trees and shrubs now?

• During more typical weather conditions, February is often ideal for winter pruning. In most cases, trees and shrubs can be pruned up until just before bud break.
• However, this year many trees and shrubs have already surpassed that phase and winter pruning activities should be delayed.
• If your tree or shrub is showing signs of emerging from winter dormancy, like exhibiting swollen buds or if buds have already opened up, then it is best to hold off on winter pruning for this season. 

Lawns

• The most important thing regarding lawns right now (and every early spring) is patience. The lawns are not typically growing yet and any damage or stress caused by doing too much this early (like dethatching) could stress them if there is another cold snap. 
• Even though air temperatures are warmer, soil temperature is the key driver for when the lawn will start growing. Lawns really won’t start waking up until soil temperatures get above 45°F (this generally happens when air temperatures are in the 50s and 60s consistently). Our current soil temperatures are still in the high 30s for most of Minnesota. 
• It is too early for a pre-emergent herbicide (crabgrass preventer) application. These products work best when applied right before summer annual grassy weeds begin germinating (around soil temperatures of 50°F). Check out the Turf Dashboard for help on when is the best time for applying a crabgrass pre-emergent.  
• The lack of snow cover for most of Minnesota this winter may or may not affect our lawns.
  • Snow mold pressure may be lower this year, but the risk of other winter injury is still there.
  • The lack of insulating snow cover can mean lower soil temperatures and increased winter desiccation (drying out).
  • We won’t know the extent of any winter injury (if any) for several weeks when things come out of dormancy.
• So besides being patient, what else can people do with their lawns?
  • Right now is still a great time to dormant or frostseed any areas that might be thin. There are surely going to be several more freeze/thaw cycles that will help work the seed down into the soil for you, ensuring optimal seed-to-soil contact. 

Insects

How insects are doing with this warm winter depends on which bug you are talking about.

• Some bugs aren’t in Minnesota right now, for example, the migratory Monarch butterfly. Counts of their populations in Mexico and California are starting to come out but will be unaffected by what is happening this winter in Minnesota.
• Insects that spend the winter here overwinter as eggs, immature (like caterpillars or grubs), pupa, or adults. They might be underground or hiding in bark, in a hollow stem, or in a pile of leaves. This creates a lot of variability in how each species will respond. One thing they all share is that they can’t make their own heat; they are totally dependent on the environment for the warmth they need to move, grow and eat. 
• If the ground is still frozen in your area, insects that are underground, like the white grub of Japanese beetle, will still be hanging out in the cold temperatures.
• The insects that spend the winter in our houses, like brown marmorated stinkbug and multicolored Asian ladybeetle, might start to wake up and slowly crawl around the house. The insects, like us and our plants, are waiting out the weird winter, and they can’t do anything about it.
• If we want to help insects get through this winter, one thing we can do is leave stuff where it is. It can be tempting to get into spring cleaning now, but if we tidy up leaves and dead stems we left in the fall, we are also going to get rid of the bees and butterflies that spend the winter in those materials.

Fruits 

Warmer temperatures (above 50 degrees F) in February and March can have more influence on trees coming out of dormancy sooner than warm temperatures in December and January when the trees, in general, are in a deeper dormancy.

In Minnesota, fruit trees are pruned when they are dormant. This reduces the potential for fungal and bacterial disease damage and gives the plants time as they exit dormancy for the pruning cuts to heal.

Factors gardeners and growers might want to consider when deciding when to prune include how many trees they have to prune for the season.

• If you have acres of trees, you might want to start earlier. Consider the temperature and moisture levels outside when making pruning cuts.
• Most fungal spores need moisture and temps above 50 F to be active. This is why we recommend pruning on a colder, dry day.
• If you are concerned about fire blight on wood, be sure to disinfect tools between cuts.
  • See Cleaning and disinfecting tools.

A note about apple tree pruning

• While pruning grapes during budswell or later can create a risk of introducing trunk diseases and potentially knocking off developing buds due to their sensitive nature, apple trees can be pruned closer to budswell or even at bloom.
• For some growing systems, this method of late pruning can be an effective way to control how many apples will set that year on a given tree.
• Apple branches exhibiting fire blight canker are most effectively pruned and removed when a tree is dormant.
• See Growing apples in the home garden including our pruning apples video series.