Dear Master Gardener: New trees were planted along Highway 371 last fall after road construction and seem to be struggling to survive. Should they have been planted in the spring instead of the fall? Kentucky coffee trees and swamp white oaks were planted. How common are they in this area?
Answer: Some shrubs and trees are off to a slow start this year, so they may be slow to bud out. Kentucky Coffeetrees in particular have a long dormancy period. In our area, bareroot trees and shrubs are best planted when they are dormant in the spring or in the fall. Balled and burlapped and container-grown plants can be planted throughout the growing season, but with caution during the summer months. The periods of heat and drought that we often see during the summer are tough on newly planted trees and shrubs. The advantage to planting trees and shrubs in the fall versus the spring is the warmer soil temperature along with cooler air temperatures creates a good environment to get a root system developed.
Proper watering is the most important practice to ensure survival and establishment of trees and shrubs. Newly planted trees and shrubs should be watered at planting time, then daily for one to two weeks. From three to twelve weeks, water every two to three days, then after twelve weeks, water weekly until the roots are established. Apply water directly over the root ball and keep the backfill soil in the planting hole moist to encourage the roots to expand beyond the root ball into the backfill soil. In Minnesota, tree roots grow approximately 18 inches per year, so expand the area being watered over time.
The Kentucky Coffeetree is native to the Midwest, but not commonly found in Minnesota. Its range lies in the southeastern part of the state. It was listed as a Minnesota Special Concern species in 2013 due to the difficulty of getting the seeds to germinate, and its small natural populations and limited range in the state. It is a moderate growing, long-lived tree that requires full sun. It is a large tree that reaches 50-70 feet, and sometimes 100 feet, with a diameter of two to three feet. The University of Minnesota released True North in 2015, its second Kentucky Coffeetree, which is notable for its narrow, upright-oval form, superior branch architecture, and lack of fruit and seeds. As a cautionary note, the leaves, seeds and pods are very poisonous to humans and animals.
According to the Minnesota DNR, the swamp white oak is common in river bottoms in the extreme southeastern corner of Minnesota and in the southern part of the Minnesota River Valley. It rarely grows as far north as St. Paul. It is slow growing, moderately shade tolerant, and as its name implies, it requires moist soil.
Dear Master Gardener: I heard that there is an invasive worm found in bags of mulch. Will they harm my garden if I inadvertently buy a bag of mulch that has them in it?
Answer: The invasive worm that you are referring to is the jumping worm, also known as Alabama Jumpers or Crazy worms. These worms move like a snake and sometimes seem to be jumping. They are identifiable by a light-colored ring that extends around its body. Researchers at the University of Minnesota have confirmed jumping worms in Minnesota. They, and their eggs, may be distributed in commercial mulch or from community compost piles. They are able to survive in shredded pine, cedar and spruce mulch and have often been observed in mulched garden beds. No earthworms are native to Minnesota. Jumping worms are native to Asia and spread by moving potted plants, soil, compost, mulch and fishing bait. They are able to rapidly infest gardens and forest floors and will transform the topsoil and mulch into dry, granular pellets that look like coffee grounds. They strip important nutrients from topsoil, which combined with the lack of an organic layer, kills fragile plants and increases erosion. This means invasive species like buckthorn can completely take over an affected area. If your soil looks like coffee grounds and you find unusually active worms in your mulch, you may have jumping worms. Report any suspected jumping worms to the DNR. Remove and destroy them if you see them by sealing them in a bag and throwing it away in the trash.
Dear Master Gardener: I purchased a Mandevilla and a friend purchased a Dipladenia and they look alike. Are they the same plant with different names?
Answer: Mandevilla or Dipladenia vine is a tropical vine that is commonly found in garden centers right now. You may sometimes see the plant referred to by either name. According to Clemson University, the genus Mandevilla includes plants that were formerly called Dipladenia. Older varieties of Mandevilla were all climbing vines, but there are some newer varieties that have mounding, bushier habits and do not need supports to climb up. This vine produces gorgeous, trumpet-shaped flowers that attract hummingbirds. It needs full sun and is a non-stop summer bloomer.
University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. All information given in this column is based on university research. To ask a question, call the Master Gardener Help Line at 218-454-GROW (4769) and leave a recorded message. A Master Gardener will return your call.