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 should I prune large, overgrown lilacs?

Proper pruning can renew or rejuvenate large, overgrown lilacs and other deciduous shrubs. One way to prune old, neglected lilacs is to cut them back over a three-year period. Begin by removing one-third of the large, old stems at ground level in late winter (March). The following year (again in late winter), prune out one-half of the remaining old stems. Also, thin out some of the new shoots. Retain several well-spaced, vigorous, new shoots and remove all the others. Finally, remove all of the remaining old growth in late winter of the third year. Also, do some additional thinning of the new shoots.

A second way to renew a large, overgrown lilac is to cut the entire plant back to within 4 to 6 inches of the ground in late winter. This type of renewal pruning will induce many new shoots to develop during the growing season. In the following year, select and retain several vigorous, well-spaced shoots and remove all others at ground level in late winter. Head (cut) back the tallest shoots to just above a bud to encourage branching. Large, overgrown dogwoods, privets, spireas, honeysuckles and forsythias can also be rejuvenated in this manner. Most lilacs renewed by this method will not bloom for two or three years.

When leafing through a garden catalog, an onion variety was described as a long-day type. What is meant by the term long-day?

Onion bulb formation begins when a certain day length is reached. Short-day onion varieties begin to form bulbs when they receive 10 to 12 hours of daylight, intermediate-day onions need 12 to 14 hours of daylight, and long-day varieties require 14 or more hours of daylight.

Bulb size is largely determined by the number and size of the leaves at bulb initiation. The larger the tops (foliage area) at bulb initiation, the larger the bulbs will be. (The size of onion bulbs also depends on weather, soil conditions and other factors.)

Long-day onion varieties are the best choice for gardeners in Iowa and other states in the upper midwest. Short-day varieties generally produce small bulbs when grown in northern areas because of the small amount of foliage present at bulb initiation. Long-day varieties, however, are able to produce large tops before bulb initiation occurs. As a result, long-day onion varieties typically produce the biggest bulbs.

When is the best time to prune grapevines?

The most desirable time to prune grapevines is late winter or early spring. In Iowa, pruning can be done from late February until early April. Grapevines pruned at this time of year may bleed heavily. However, the bleeding doesn’t harm the vines.


Contacts :

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

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


A high resolution version of the onion photo above suitable for printing is available here: [ Onions2-15-06.jpg ] 8.5 MB