Trees and Shrubs

Bur Oak – Propagating seeds:  I picked up some acorns from a Bur Oak tree while visiting my parents’ farm. What is the best way to sprout those seeds?

Answer: Bur oak (Quercus macrocarpa) is a stately native tree of Kansas. One of the state’s largest trees, it attains a height of 70 to 80 feet. Unfortunately it is slow growing. According to the Manual of Woody Landscape Plants by Michael Dirr, Bur Oak seeds do not require any special treatment for germination. However, applying cool treatment will improve germination. Place the acorns, with the hull removed, in a bag with moist sand or peat moss in the refrigerator for 30 to 60 days. Check occasionally to make sure the sand remains moist.

After the cool treatment, plant the acorns in the garden or in pots at a depth of two to three times their diameter. Keep the soil most and wait for germination. Be patient because it may take several months or more for the seedling to emerge.


Christmas trees – Living: My family would like to purchase a living Christmas tree instead of a cut tree. What advice can you give me for helping to ensure this live tree survives the Kansas City climate?

Answer: Living Christmas trees are a great way to keep the holidays alive in a family’s memory. Live trees should be kept in the house less than a week. If the tree is left in the home too long, the branches will dry out, decreasing the chance of survival. Wrap the root ball in plastic to retain moisture and place it in a large container. It is extremely important not to let it dry out. In addition to keeping the root ball moist at all times, misting will also be beneficial to the tree.

It is a good idea to dig the planting hole before the ground freezes. This will make planting easier and not as weather dependent. After the holidays, move the tree outdoors and remove the plastic wrapping. If the temperature is below 25 degrees, hold the tree in the garage or an unheated area for a week or two, keeping it moist. This allows the tree to adjust slowly to the winter temperatures. Once the adjustment period is over, the tree can be planted in the landscape. The tree needs to be watered well over the winter so it will become well established. Enjoy!

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Corneliancherry dogwood: On a recent trip to the east in the spring, I saw a yellow flowering tree called corneliancherry flowering dogwood. Do you know anything about this plant and will it grow in Kansas City?

Answer: Corneliancherry dogwood is an under-used plant in this part of country. The botanical name is Cornus mas. It is a small, shrubby tree reaching a height of about 20 feet. Kansas State University had specimens that bloomed magnificently every spring. The plant is a real winner for spring color and is very adaptable to Kansas City conditions. It is best used in a shrub border or as a small, multi-branched tree in the landscape.


Curly Willow: At a recent garden show, one booth had different kinds of tree branches for sale. One that caught my interest was called a curly willow. Will that plant grow here?

Answer: Curly willow will grow in our area. Salix matsudana ‘Tortuosa’ is a small tree reaching twenty to thirty feet in height. Like most members of the willow family, it is fast growing and weak wooded. The plant is also short lived due to several disease problems. The curly willow can be grown for its unusual characteristics of twisted branches. Expect the tree to last around ten years before starting to decline. Floral arrangement designers love the stems for the unusual lines they provide in arrangements.

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Ginkgo trees – Pruning: I was going to prune my 10-year-old ginkgo tree earlier this year and the time just got away from me. When is the best time to do the pruning?

Answer: Late winter or early spring is the ideal time for pruning because there are no leaves on the tree to hide the branching structure. Pruning at this time helps make it easier to decide which branches to leave and which to prune. Reduced structure visibility when the tree is leafed out may make choices more difficult. Early spring is also the time of most rapid growth, so wounds close more quickly.  It is important for the long-term health of the tree that proper pruning practices be followed. There is never a bad time to prune to correct a growth defect in the tree or to remove a dead or dangerous branch.

Magnolias: Two of the plants at my new home were favorites of the previous owner. They are Star and Saucer Magnolias. What can you tell me about their care and habit?

Answer: Saucer Magnolia, Magnolia x soulangiana, is a small, shrubby tree that reaches a height of 20 to 30 feet. It is best known for its showy, large pink flowers that emerge in very early spring. Unfortunately, the buds are frequently nipped by a late frost that turns the petals an oily black color. The plant is fairly adaptable to the Kansas City climate but would benefit greatly from a little extra water during stressful summers.

Star Magnolia, Magnolia stellata, is a smaller plant reaching 15 to 20 feet tall with equal spread. This plant has white flowers early in the spring that also run the risk of being killed by a freeze. The plant has dark green leaves during the summer and a nice, bronze fall color. Like the Saucer Magnolia, it will tolerate most conditions. It is best to avoid planting these trees on a southern face of a building to help prevent early blooming. Both plants have few insect and disease problems.

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Magnolia, Sweet Bay:  I have noticed a small tree in the area called a Sweetbay Magnolia. I love magnolia blossoms. Can you tell me more about the plant?

Answer: Sweetbay Magnolia, Magnolia virginiana, is a small multi-stem tree that is increasing in popularity. It will reach about twenty feet in height at maturity. The leaves, often lustrous on top and silvery underneath, are light to dark green depending on location. Creamy white flowers appear from May until June. Unfortunately, they are not usually available in great numbers. Sweetbay Magnolia would make a great addition to a patio planting or as a specimen in the landscape. For best growth, this plant prefers an evenly moist, acidic soil in a light shade to partial sun exposure.


Mulching around trees:  I have noticed that a lot of professional firms mulch trees with wood mulch in a cone formation around the base of trees. Is this a good idea?

Answer: Mulching around trees is recommended, but this practice is extremely devastating. Mulching materials that come into contact with the tree trunk will severely weaken or even kill the tree. The constant moist conditions created by the mulch will rot the bark layer and damage the cambium (growth) layer of the tree. It is recommended that mulch about four inches deep be spread around the tree but kept a few inches away from the tree trunk. The rule of thumb is to build donuts, not pyramids, around trees.

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Rose-of-Sharon: My old Rose-of-Sharon died this spring. I always thought they were as tough as nails. What happened to the plant?  

Answer: In the past, most people thought Rose-of Sharon was a hardy plant that thrived under many harsh conditions. But many gardeners lost well-established plants as a result of hot, dry summers and early freezes. It was realized that the plants were stressed and unable to withstand these severe conditions. Because there are few plants that offer summer color, gardeners may choose to re-plant Rose-of-Sharon. However, they should be aware of the effect that severe summer stress may have on the plant.


Shrubs – Off-color in winter: I have noticed that many of my evergreen shrubs, junipers and boxwoods are developing a brownish color or lighter green cast. What is the cause of this and should I be worried?

Answer: The discoloration of evergreen shrubs over the winter is a common occurrence in this area. The effects of cold temperatures and chilling winds normally result in this off-cast coloration. It is part of the plant’s response to the changing of the season. Usually this effect is mild and not long-lasting. However, during extremely cold winters, a foliage loss or twig dieback can occur, depending on the type of plant.

If extremely dry conditions occur during the winter, the off color could be the result of drought. Evergreens tend to use and lose more moisture over winter than deciduous plants. Dry conditions will weaken plants and their roots, which could result in a decline in growth or death. To help overcome a dry soil condition, an occasional deep soaking during the winter is recommended.

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Spirea – Pruning:  A few years ago I planted two varieties of spirea in my yard, ‘Anthony Waterer’ and ‘Gold Mound.’  They looked great and bloomed nicely for the first few years. Last year they became quite messy looking and unattractive. Is there anyway to prune these plants to recapture the look they once had?

Answer: As spirea age, they become woody or stemy and develop a less attractive habit. One way to overcome this is to severely prune the plants. In fact, removing all branches to a height of about three inches from the ground will cause new branches to grow from the base. This will renew the plant and give it a much younger appearance. Another option would be to remove about one-third of the oldest growth each spring. This also renews the plant and results in a nicer form.


Tree sap – Dripping:  I pruned my River Birch while it was dormant and now sap is dripping from a few of the cuts. What can I do to stop it?

Answer: River Birch is best pruned after the tree fully leafs out. Pruning while the tree is dormant will often result in the excess flow of sap, which is a short-term problem. There is no need to apply anything or do anything. You have not hurt the tree and it will not bleed to death.

Keep in mind that maples are also prone to this problem and are best pruned after leafing out.

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White Pine - Brown needles on:  In the spring I noticed that the needles on my White Pine turned brown. If this is a disease, what do I do about it?

Answer: The discoloration of the needles was probably caused by a mid-winter cold spell. Cold temperatures and winds dry out the needles resulting in the brown coloration. Many of our evergreens, including pines, spruce, boxwood, and hollies, can suffer winter damage. At this time there is nothing to do but wait. New growth should emerge and cover the unsightly needles or they will fall off. The best prevention from this type of damage is to make sure all evergreens go into the winter with sufficient soil moisture. Extremely dry summers and falls can also contribute greatly to this problem.

Winter tree leaves:  My maple and elm trees have held their leaves for such a long time. Normally by late fall or early winter the leaves have all dropped off. Why are all the leaves still on the trees?

Answer: The process of leaves falling is known as abscission. The abscission layer is caused by a hormonal change in the plant in response to changes in temperature, length of daylight, and a natural senescence or aging. During years when there are hard freezes in early October, the plants do not have sufficient time to develop the abscission layer. As a result, the leaves simply freeze and remain attached to the branches. Winter wind and moisture will cause the leaves to drop from the tree. This phenomenon should not be harmful to the plant. The only danger is a very heavy snow or freezing rain. This added weight of moisture due to the leaf surface will increase the chance for limb breakage.

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