Extension News

Ask the ISU Experts

Note to media editors:

Got gardening questions? Contact the Hortline at (515) 294-3108 (M-F; 10-12 & 1-4:30) or send an e-mail to hortline@iastate.edu. For more gardening information visit us at Yard and Garden Online at www.yardandgarden.extension.iastate.edu


How should I prune my Heritage red raspberries in late winter? 

 Heritage is a fall-bearing variety of red raspberry. Other popular fall-bearing red raspberries include Redwing and Autumn Bliss. Fall-bearing red raspberries naturally produce two crops. One crop is produced in summer on the previous year’s growth. A second crop is produced in late summer or early fall at the tips of the current year’s growth. 


Fall-bearing red raspberries can be pruned two different ways in March or early April. 


One pruning option is to prune out all weak, diseased and damaged canes at ground level. Leave the largest, most vigorous canes. Cut back the tips of the canes that remain.  Remove approximately the upper one-third of the canes. This option provides two crops during the year. 


The second option is to prune all canes back to the ground in late winter/early spring. This pruning option produces a single crop in late summer or early fall. (The summer crop is eliminated.) While only one crop is produced, total crop yield is actually larger than the two crop system. 


Red raspberries sucker profusely. Maintain plants in a 1- to 2-foot-wide hedgerow using a rototiller or spade. 


When should dormant oil sprays be applied to fruit trees? 

Dormant oil sprays are highly-refined petroleum products that are mixed with water and applied to trees and shrubs to control aphids, spider mites and scale. Dormant oils destroy pests by suffocating them. When applied properly, the thin film of oil plugs the spiracles or pores through which the mite or insect breathes. 


Proper timing is critical when using dormant oil sprays. Dormant oils should be applied in late March or early April before the plants show signs of breaking dormancy (before “bud break”.)  Dormant oils applied in February or early March are not effective as insects are not actively respiring at this time and, therefore, are not vulnerable to the oil’s suffocating effects. Dormant oil sprays should be applied as close to bud break as possible. 


Dormant oil sprays on fruit trees provide little benefit to most backyard gardeners. Dormant oil sprays do not control the major home orchard pest, the apple maggot, and the pests that are controlled by dormant oil sprays are seldom significant. 


It’s only February, but my tulips are coming up.  What should I do? 

Tulips, daffodils and other spring-flowering bulbs normally begin emerging from the ground in March or early April in Iowa. However, mild winter weather can encourage premature growth. The early emergence of spring-flowering bulb foliage is most often seen on the south and west sides of homes and other buildings. These areas are usually warmer than the rest of the yard because sunlight is reflected off the building to the ground. In addition, heated basements keep the soil near buildings relatively warm. 


While the premature emergence of spring-flowering bulb foliage is undesirable, the danger is not as great as it may seem. The foliage of tulips, daffodils and other spring bulbs can tolerate cold temperatures. Often, normal winter weather (cold temperatures and snow) returns, delaying further growth. A blanket of snow is especially helpful. The snow discourages additional growth and also protects the foliage from extreme cold. 



Contacts :

Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu

Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

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