Lawn and garden season is back!
The weather is getting warmer, the days are getting longer, the snow is melting and we are anxious to get out and scratch around in our gardens and see what has survived the cold of winter. But we who live in Minnesota, know that we must still wait much longer before we can plant or actually see any plant growth. It is this patient waiting that makes us such aggressive and committed gardeners when we can finally can get out and work. One thing that we should do now before April 1, is prune our deciduous trees and shrubs (unless they are the type that will be blooming on old wood).
Shrubs which bloom on old wood should not be pruned now because they will not bloom this spring if the part that bears the blossom is cut off. In zone 3 this would include bridal wreath, chokecherry, crabapple, flowering plum or cherry, forsythia, lilac, ninebarks, spirea, viburnum, and weigelas. These should be pruned immediately after they have bloomed so they have time to develop a healthy growth for next year's branches and flower buds. If you are in doubt that you will prune off the blossoms, wait until your plant has bloomed and if it needs to be cut back, prune it then.
Deciduous trees respond best to pruning just before waking up from dormancy in late winter or early spring. This leaves fresh wounds exposed for only a short time before new growth begins the wound sealing process. This is also the best time to see winter damage and make pruning decisions without leaves obscuring plant branch structure. Autumn or early winter pruning is more likely to result in drying out and die-back at the pruning sites.
When pruning trees and shrubs, always make and angled cut just above and parallel with the angle of the visible bud. If the cut is too close to the bud, it will cause the bud to dry out and die. If the cut is too far above the bud, a stub will remain which will eventually die, rot away, or provide a possible entryway for disease.
Pruning helps to keep your trees and shrubs in top condition. Check your trees for dead and broken branches, and branches that are rubbing together. Wounds such as these cause irregular surfaces which usually affect more surface area and thus take longer to heal than clean cuts. This allows more opportunity for pest and disease to enter.
If you have chokecherry or cherry trees which have black knot disease, these should be cut back six inches into live healthy wood (usually evident by the presence of visible buds). If you are not sure if a branch is dead or alive, gently scrape the bark with your pruners to reveal the color of the growth layer underneath. Green means it is alive, brown means it is time to prune. By cutting off the diseased part, you stop the advance of the disease. If you are working with diseased branches it is a good idea to dip your pruning tools in alcohol or a 10 percent bleach solution between cuts.
Thinning or removing entire stems or branches is another pruning technique that is done to keep shrubs and trees productive and encourage new growth. Remove old decrepit stems that have declined in flower production or that have grown too tall. These should be pruned back to the ground or to a vigorous shoot near the base. This will increase light and air circulation in the center of the plant, and stimulating new shoots to grow. Some of the young stems also may need to be removed to allow room for this new growth. Shrub trimming should be done on a regular basis to that the shrub will uniformly renew itself over time.
Suckers are vigorous vertical stems that ruin a tree or shrubs appearance. There are two types of suckers, water spouts (which originate on branches), and root sprouts (which grow from the base of the tree). Water sprouts create too much shade within the crown of the tree and slow flower and thus fruit production. Root sprouts compete with and eventually overgrow the trees trunk. If it is a grafted tree, the root sprouts will not have the desired form, leaves, flowers, or fruit, because it will be a sprout from one of the parent tree. Suckers need to be removed back to the growing point. If a sucker is not removed all the way back to its growing point, new suckers will start growing from the base of the original sucker.
To avoid oak wilt disease DO NOT prune oaks during April, May and June. If oaks are wounded or must be pruned during these months, apply a wound dressing or latex paint to mask the odor of freshly cut wood which attracts beetles that spread oak wilt disease.
Kyle Schulz is a Wadena County Master Gardener from Sebeka, and the regular gardening columnist for the Wadena Pioneer Journal.