Extension News

Ask the ISU Experts

Note to media editors: Got gardening questions? Contact the Hortline at (515) 294-3108 (Monday-Friday; 10 a.m.-12 noon and 1-4:30 p.m.) 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 do I germinate acorns? 
Acorns should be collected as soon as they fall to the ground. Sound, viable acorns can be separated from damaged or unfilled acorns by placing them in water. Sound acorns will sink.  Most floating acorns are not viable and can be discarded. 
The acorns of white oak (Quercus alba) and swamp white oak (Quercus bicolor) should be planted in fall. They will germinate immediately after sowing. 

Acorns of bur (Quercus macrocarpa), pin (Quercus palustris) and red (Quercus rubra) oaks will not germinate until they have been exposed to cool temperatures and moist conditions for several weeks. Winter weather in Iowa normally provides the necessary conditions to break dormancy. The cold-moist requirement can also be accomplished through a process called stratification. Acorns can be stratified by placing the seeds in a moist mixture of sand and peat moss and then storing them in a cool location. Suitable containers include coffee cans, plastic buckets and food storage bags. The refrigerator is a good storage location. (Stratification temperatures should be 32 to 41 degrees F.)  Acorns of the bur oak require a 30 to 60 day stratification period, while red oaks and pin oaks require 30 to 45 days. Acorns of bur, pin and red oaks can be planted in fall or stratified seed can be sown in spring. 

When planting acorns, place the seeds 0.5 to 1 inch deep. Choose a planting site where the oak seedlings can receive good care for one to two years before they are transplanted to their permanent location. 

Are the fruits of viburnums safe to eat? 
The fruit of several viburnum species are edible. The fruit of the American cranberrybush viburnum (Viburnum trilobum), nannyberry (Viburnum lentago) and blackhaw viburnum (Viburnum prunifolium) can be made into preserves and jellies. 

Why are there flowers on my crabapple in September? 
Apple scab is a common fungal disease of apples and crabapples. Cool, wet weather in spring favors apple scab development. Apple scab appears as velvety, olive-green to black spots on the crabapple leaves. Heavily infected leaves turn yellow and fall from the tree.

In 2007, crabapple varieties that are highly susceptible to apple scab lost most of their foliage by mid-summer. The stress associated with the extensive leaf drop may have induced some crabapples to become semi-dormant. 

The flower buds on crabapples and most other trees and shrubs form in mid-summer. The abundant rainfall and cooler temperatures in late summer may have partially revived some of the semi-dormant crabapples and coaxed a few flower buds to open. 


Contacts :

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

Jean McGuire, Extension Communications and Marketing, (515) 294-7033, jmcguire@iastate.edu