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Hort Update Feb. 16, 2015

oystershell scale
Physical removal of oyster shell scale on an aspen. Photo by Whitney Crenshaw, Colorado State University.
Lawns Major Symptom:
1. Winter injury Avoid walking on ice covered or frozen turf
2. Dormant seeding Consider dormant seeding if conditions allow
Trees & Shrubs  
3. Squirrel damage Twig clipping and bark stripping in mid to late winter
4. Check for scale insects Inspect stems of dogwood, lilac, Euonymous, maple, oak
5. Storm damaged branches Allow ice to melt naturally; keep safety in mind
6. Hiring an arborist Tips for hiring an arborist
7. Corrective pruning Dormant season good time to prune for strong structure
8. Prune summer flowering shrubs Use a combination of heading back and thinning cuts
9. Great Plants for the Great Plains  Select a GreatPlant to add diversity to landscape plantings
Landscape Ornamentals  
10. Clematis pruning Based on plant flowering time and bud growth on new or old wood
11. Vole damage to bulbs Possible damage to flower bulbs, perennials
Fruits & Vegetables  
12. Time to prune out black knot Prune and destroy branches with galls before April 1st
13. Remove fruit mummies To reduce disease pressure in fruit trees
14. Planning vegetable gardens Finalize plans for garden rotation & succession, purchase seeds, germination tests, and sterilize pots
15. 2015 Gardening Trends Edible gardening remains strong


1. Winter Injury - As snow melts or winter rains occur, this water may be taken up by turf plants if temperatures are warm enough (crown hydration). Ensuing cold temperatures may freeze that water inside the plant, which is called crown hydration injury. The best defense to limit crown hydration is to maximize surface and subsurface drainage to minimize wet areas.  Another form of winter injury is direct cold temperature kill which is caused by dramatic swings down to very cold temperatures. This is most common on seedlings and occurred in many areas of Nebraska in May of 2014 on new seedlings on golf courses as a result of winter kill during 2013-14 (the one primary risk with dormant seeding). Another form of winter injury is from too much traffic on dormant turf at a time when it can't recover. Winter golf of over-using soccer fields during the winter are the usual causes. Yet another form of cold temperature damage is from traffic on frosted areas. This requires green living tissue that is damaged by physical abrasion of frost (ice crystals) with even light traffic. It is best to minimize winter traffic on any turf area and especially if frost is present on green turf. Winter traffic can cause cosmetic damage, physical abrasion, and/or soil damage depending on the situations.

Comprehensive Guide to Winter Turf Damage and Recovery in the Northern United States, University of Nebraska Turf iNfo


2. Dormant seeding involves seeding while the ground is not frozen, but cold enough that seed germination will not occur until after soils begin to warm in spring. Other than the time of year of dormant seeding, typically mid-December through Valentines Day or Spring Break, the actual process of preparing the area to be seeded is the same as for seeding at other times of the year. If seedbed preparation took place last fall, and soils are not frozen, dormant seeding can take place now. The risk of dormant seeding is warm winter and early spring temperatures may cause seed to germinate and then a subsequent cold period kills the seedlings. When using dormant seeding, monitor seeded areas in mid spring for the need to do additional overseeding.

Establishing Lawns from Seed, University of Nebraska Turf iNfo


3. Squirrel Damage - Squirrels may damage trees during winter and spring by stripping bark or clipping off twigs to access sap for moisture. They may also feed on tree buds. Occasionally, tree squirrels gnaw on decks, porches, fences, and other objects; most likely for marking territory. While trees can withstand quite a bit of squirrel damage, the wounds may lead to other issues or stress. If a tree needs protection, metal collars can be installed around the trunks of shade trees; or polybutene-based repellents may be applied to help reduce squirrel damage. To prevent tree damage from the repellent itself, be sure to follow label directions for application. For structural gnawing, use a physical barrier such as metal flashing. If this is not an option, commercial repellents may be effective. Apply the repellent on the marks and to a 12-inch radius around the gnawed area; and repeat as necessary.


4. Scale Insects - The dormant season is a good time to check woody plants for scale insects. Without leaves on plants, overwintering scales are easier to see on stems. Scale insects are easily overlooked because they are small and immobile most of their lives; and they do not resemble a typical insect. Many scales resemble small oval or circular shells that are white, tan or brown. To the inexperienced eye, scales can appear to be a normal part of the bark. Some plants to inspect for scale insects are dogwood, lilac, Euonymous, apple and pear. If scales are found, infested branches can be pruned out and destroyed or a dormant oil can be applied in March when temperatures are above 40 degrees. Continue to monitor infested plants as scale populations can increase dramatically during the growing season. If not controlled, heavy infestations can kill branches and entire plants.

Oystershell Scale, Colorado State University


5. Storm damage to large trees from snow or ice is best handled by a certified arborist. When storm damage occurs during winter, immediate care should focus on removal of broken branches and other safety issues. Leave finishing cuts to later to prevent wound drying during winter. An improper finishing cut such as a flush cut or stub cut, as well as the use of wound dressings or paints, will increase the incidence of decay in wounds. Avoid fertilizing storm damaged trees with nitrogen fertilizer. Most Nebraska soils have adequate fertility for trees and excess nitrogen can do more harm than good.

Immediate Care for Storm Damaged Trees, Nebraska Forest Service


6. How to hire an arborist - Hiring an arborist to properly care for trees is an investment that can add considerable value to property. A certified arborist is trained in planting, caring for and maintaining trees. Certified arborists have at least three years experience and have passed an exam developed by some of the nation's leading experts on tree care. Hiring an arborist is a decision that shouldn't be taken lightly. Poorly maintained trees can be a significant liability to homeowners. Pruning or removing trees, especially large trees, can be dangerous and should be handled by a professional.

An arborist can provide many services, such as pruning. Arborists can determine what type of pruning is necessary to maintain or improve the health, appearance and safety of trees. These techniques include eliminating branches that rub each other, removing dead or weak limbs that pose a hazard or may lead to decay and removing limbs that interfere with wires, building facades, gutters, roofs, chimneys or windows. Arborists also can train young trees and thin or remove unnecessary branches.

How to Hire an Arborist, Nebraska Forest Service


7. Corrective tree pruning helps avoid long term structural issues in trees. Hire a certified arborist to prune larger trees. Corrective pruning includes removal of:

  • A double leader
  • Branches that are crisscrossing and rubbing against another branch or one that will eventually rub if left to grow larger
  • Closely parallel branches that may eventually grow into one another
  • Branches with very narrow forks that can lead to included bark and weakened branch attachment

Pruning Trees, Nebraska Forest Service


8. Prune summer flowering shrubs during winter. These shrubs develop flower buds on new growth. Avoid pruning spring blooming shrubs as flower buds developed last summer and will be removed by pruning. When pruning shrubs, avoid using only heading back cuts that shorten all of the branches to the same height. This encourages dense growth on branch ends that eventually shades out the lower half of the plant. Use a combination of heading back and thinning out cuts. Heading back cuts remove a branch just above an outward facing bud to reduce a shrubs height. Thinning out cuts completely removes a stem back to another branch or at ground level, allowing sunlight to reach into the center of the shrub.

Pruning Trees, Nebraska Forest Service


9. Great Plants for the Great Plains - When selecting landscape plants, think diversity. Select plants that are adapted to the growing site but do not overplant one species in a landscape or in a neighborhood. For ideas on good plants to consider, check out the GreatPlants program. The Nebraska Statewide Arboretum names landscape plants each year that should be considered more often for Nebraska landscapes. This year's GreatPlants are black oak, Quercus velutina; red pine, Pinus resinosa; buttonbush, Cephalanthus occidentalis; Carolina lupine, Thermopsis villosa; and giant sakaton grass, Sporobolus wrightii.

GreatPlants, Nebraska Statewide Arboretum


10. Clematis pruningcan be one of the most confusing things about growing them.  The main reasons for pruning are:

  • to establish a neat and tidy framework,
  • to stimulate the development of buds and flowers, and
  • to encourage growth. 

There are three general methods of pruning clematis and each is based on 1) flowering time and 2) whether or not the flowers are produce on stems from this year's growth or on stems from previous year's growth.  Improper pruning is a common reason gardeners are disappointed in the flowering of their clematis plant. 

Image of pruning techniques for clematis groups 1, 2 & 3.

Pruning Group I: Species and cultivars in this pruning group flower on old, mature stems. Most are spring flowering. This group requires little or no pruning. However, they can be cut back and tidied up after the main flowering period has ended or if they have overgrown their space.

Pruning Group II: Species and cultivars in this group produce two flushes of flowers. The first occurs in spring on old, mature growth from the previous year, while the second flush occurs during late summer on the current year's growth. Remove dead and damaged stems in late spring. If more pruning is necessary, do it immediately after the early flowering period. Shoots can also be pruned back to encourage re-blooming.

Pruning Group III: This group of plants is the easiest to prune. They usually flower on the current year's new growth in spring to late summer. Annual pruning can be done in late winter or early spring, cutting back all the old stems to the base of the plant.


11. Vole damage to bulbs - Flower bulbs may be eaten, and other ornamental plants eaten or clipped by hungry voles. They may clip off young plants or dig up seeds. Look for tiny tooth marks about 1/16-inch wide on damaged bulbs, or for vole damage on surrounding turfgrass and woody plants to confirm their presence.

Voles are attracted to landscapes with birdfeeders, so removing feeders temporarily may be necessary until the problem is controlled. Temporary Exclude voles from high value gardens with woven-wire or hardware cloth fences (1/4 inch or smaller mesh); 12 inches high and the bottom buried 2-3 inches in the soil. Mouse traps smeared with peanut butter can be used to kill voles. Taste repellents, such as thiram and capsaicin, can be used for temporary control on ornamentals, but will need to be reapplied as directed by the label. These products are not labeled for use on plants grown for human consumption.

Voles, Nebraska Extension


12. Time to prune out black knot in fruit trees - Pruning to remove black knot infected branches is best done during winter when the black swellings/galls are easily seen. Black Knot is a fungal disease that infects ornamental plum as well as other plants in the Prunus genus like chokecherry. The disease in characterized by hard, elongated, black swellings that encircle branches. Smaller twigs usually die within a year after being infected. Larger branches may live for several years before being girdled and killed by the fungus. When black knot galls are noticed, infected twigs are best pruned and destroyed or removed before bud break, which is the infection period.

Prune at least 2-4 inches below each knot because the fungus grows beyond the edge of the knot itself. If pruning is not possible because knots are present on major scaffold limbs or the trunk, they can be removed by cutting away the diseased tissue down to healthy wood and out at least 1/2 inch beyond the edge of the knot. Burn or bury the pruned material before April 1st.

Black Knot, Nebraska Extension


13. Remove fruit mummies - Brown rot is a common and destructive disease affecting apricot and other stone fruits (cherry, nectarine, peach, and plum) in Nebraska. This fungus may attack blossoms, fruit spurs (flower and fruit bearing twigs), and small branches. As the infection proceeds, it will cover the entire fruit, causing the fruit to rot rapidly. The fruit then dries and shrinks into a wrinkled "mummy". Typically the rotted and mummy fruit remain attached to the tree. Fruit infections may spread rapidly, especially if weather conditions are conducive for disease development and the fruit are touching one another.

Sanitation is critical in effectively managing brown rot. During the dormant season, mummified fruit and cankers should be pruned and either burned, buried deeply in the soil, or sent to the landfill. This will reduce the amount of overwintering inoculum present.


14. Planning vegetable gardens - Now is a great time to make a plan for this summer's vegetable garden. Get catalogs and order seeds and plants early for best selection. For suggestions of recommended vegetable cultivars to try in your garden, review Selected Vegetable Cutivars for Nebraska.  A list of many reputable companies to consider can be found at - General and Specialty Mail-Order Seed Sources.

Garden rotation of plant families helps reduce disease and insect pressure, and manage soil fertility, although it can be difficult to accomplish in small gardens.  For more information: Crop Rotation in the Vegetable Garden, Iowa State University.

Check the viability of seeds you have stored over the winter by placing 10 seeds on a moist paper towel and fold it over to cover them. Place the towel in a sealed plastic bag to maintain moisture. Label it with the seed name and date. Place the plastic bag in a warm location, 70-75 degrees, out of direct sun. Check the bag periodically and remoisten the paper towel if necessary. Most viable vegetable garden seeds will germinate in about 7-10 days, except parsley, carrots and celery, which are slow to germinate. Counting the number of germinated seeds gives the germination percentage; 10=100% germination, 9=90% excellent, 8=80% good, 6 to 7=60 to 70% poor germination so sow seed more thickly to achieve the desired amount of plants. Throw seed away that has less than a 60% germination percentage.

Don't start your vegetable plants indoors too early. Allow ten weeks to grow transplants of slow growing plants, such as broccoli, cabbage, cauliflower and head lettuce. Six to seven weeks allows enough time for peppers, tomatoes and eggplant. Two to three weeks ahead of the expected planting date is early enough for fast growing species such as cucumber, muskmelon, squash and watermelon. The final spring frost date for eastern Nebraska is approximately May 10th, and May 20th in western Nebraska. Count backwards from this date to establish a seeding date for your transplants.

Consider pasturizing your potting soil before starting bedding plants and vegetable transplants. Pasturization kills many soil pathogens, including fungal spores, and can be beneficial even with commercial potting mixes. Place the moistened soil in a heat-resistant pan or cookie sheet and cover it with foil. Place it in a 250-degreen oven and heat it to 180 degrees for 30 minutes. Check with a food thermometer to determine temperature. Allow the soil to cool before seeding.

Before reusing last year's pots or seed flats, clean them in a 10% bleach solution. Mix 9 parts water with 1 part bleach. Allow pots to soak in the solution for at least 10 minutes. Remove mineral deposits from plastic pots with a scouring pad, and from clay pots with steel wool or a wire brush.


15.  2015 Gardening Trends- The Garden Writers Association Foundation (GWAF) released its 2014 October Gardening Trends Research Report.  The report is the latest of a series of national consumer attitude surveys conducted by GWAF, through random phone surveys of 889 households. Findings include:

  • 44% grew edible plants in the ground last year
  • 15% grew edible plants in containers
  • 58% plan to grow edible plants in 2015
  • Insect and disease control (39%) and time (38%) are their greatest challenges.

The complete report is available through the Garden Writers Assocation. Search for "garden trends" survey.