Master Gardener Sue Morris: Pruning tips for when winter takes its sweet time leaving
Tips on when to prune trees — and what to look for as the season turns to spring — after snowpack and ice throughout the winter.
Are you ready for spring? It seemed like it would never get here and as of this writing, it hasn’t gotten here yet. Makes me think of something I just read: “The only thing I’m growing this spring is older and more irritable!”
With all the snow and ice pack this winter, it has made pruning trees very difficult. There are some evergreen shrubs that have been weighed down by ice and snow since November. What are they going to look like now? Be very careful, it might be too late now to do some pruning.
Pruning in late winter before spring growth starts will minimize the length of time fresh wounds are exposed before the tree starts active growth and can seal the wound.
If you want to avoid Oak wilt (a fungal disease), you need to prune from November through March. Do not prune oaks at all from April through October.
Prune apples, flowering crabapple, mountain ash, hawthorn, serviceberry and cotoneaster trees between February through April to reduce the spread of fire blight.
Some trees will “bleed” sap if pruned in later winter. This doesn’t hurt the tree, but it makes you feel bad when you see it. Wait to prune maple, butternut, black walnut, ironwood and beech in late spring or early summer after leaves have fully expanded.
You may have noticed that birch trees bleed sap when pruned in late winter but the University of Minnesota says this timing is preferable because it helps avoid attracting bronze birch borers, which are active during the growing season. This varmint girdles susceptible birch trees, blocking the vessels that move water and nutrients through the trees.
Shrubs grown for foliage or bloom in summer should be pruned in late winter or early spring before new growth starts. Deadhead a third of older branches to encourage new growth. Remove winter dieback. Spring blooming shrubs (i.e., lilac) should be pruned immediately after spring bloom in order to prevent cutting off buds for next year’s bloom.
Watch for sunscald, winter dieback
Not only are there be problems with the early ice and heavy snow that affected our shrubs this winter, there are two other things that affect them — sunscald and winter dieback.
Sunscald is when there are dried or cracked areas of dead bark usually on the south side of a tree with thin bark.
This happens when winter sun heats up tree bark and stimulates cell activity and then when a cloud or building blocks the sun, the bark temperature drops rapidly and the active cells in the plant are killed and the bark cracks forming a frost crack. This usually occurs in young and/or newly planted trees. Older trees have thicker bark that insulates and keeps tissue dormant and cold hardy.
The best way to prevent this from happening is to wrap the trunks of young and thin-barked trees with white guards or wrap for the winter and remember to remove the guards in the spring after last frost. Don’t use dark tree wrap, as that will absorb heat from the sun and defeat the purpose.
Winter dieback is another problem but there isn’t much that can be done to protect trees and shrubs from that.
Choose hardy plants for our zone 4 and those that will match your site conditions. Our winter temperatures and conditions vary in Minnesota. Because of this, there is not much that can be done to protect trees and shrubs from dieback. However, you can take management steps to reducing dieback. Choose hardy plants with growing requirements that match your site conditions. Avoid pruning, fertilizing and overwatering in late summer. (Don't use fertilizer after Aug. 1.)
Remember we have had drought the last couple of years. It has been said that drought stressed trees can take up to five years to be affected and by that time we have forgotten about the drought and wonder what is affecting these trees.
Greet spring with rhubarb
Nothing says spring like freshly-baked rhubarb muffins.
Hopefully, by now, rhubarb is soon ready to harvest. (This column was written the first week of April while my rhubarb was still under two feet of snow.)
Rhubarb can’t be grown in southern states, as it needs our cold and dormant winters to survive. After this winter, the rhubarb should be thriving. Here is my favorite recipe:
- ¾ cup brown sugar
- ½ cup oil
- 1 egg beaten
- ½ cup buttermilk
- ½ tsp salt
- 1 tsp vanilla
- 1 ½ cup sifted flour plus 1-2 tbsp
- ½ tsp soda
- ½ cup nuts
- 1 cup rhubarb chopped fine
Mix as given. Recipe should fill 12-14 muffin cups.
- ¼ cup brown sugar
- 1 tsp cinnamon
- ½ cup nuts chopped
Dust topping over muffin cups. Bake at 350 degrees for 15 to 20 minutes.
Master Gardener Sue Morris has been writing this column since 1991 for Kandiyohi County newspapers. Morris has been certified through the University of Minnesota as a gardening and horticulture expert since 1983. She lives in Kandiyohi County.
Julie Weisenhorn, Extension horticulture educator with the University of Minnesota, contributed to this article.