Ask the ISU Experts

Forsythia bloom
Some forsythia cultivars don't bloom reliably in Iowa because their flower buds are often killed by low winter temperatures.

Although my forsythia shrubs are vigorous and healthy, they don’t bloom well.  Why? 

Some forsythia cultivars, such as ‘Lynwood Gold’ and ‘Spring Glory,’ don’t bloom reliably in Iowa because their flower buds are often killed by low winter temperatures. The flower buds on ‘Lynwood Gold’ and ‘Spring Glory’ are hardy to -10 degrees F. Since most parts of Iowa experience winter temperatures below -10 degrees F, these cultivars often don’t bloom well in the state. When selecting a forsythia, choose a cultivar that possesses excellent cold hardiness and blooms reliably in Iowa.

An excellent forsythia for Iowa is ‘Meadowlark.’  Jointly introduced by North Dakota State and South Dakota State Universities, in collaboration with the Arnold Arboretum, ‘Meadowlark’ will bloom after exposure to temperatures down to -30 degrees F.  Flowers are bright yellow.  ‘Meadowlark’ is a vigorous, rapidly growing shrub. Its height and width are 8 to 10 feet.  ‘Meadowlark’ has a spreading, arching form. 

‘Northern Sun’ is another good choice for the upper Midwest. Introduced by the University of Minnesota, ‘Northern Sun’ will flower after temperatures drop to -30 degrees F. The spreading, arching shrub grows 8 to 10 feet tall and has a similar spread. Flowers are yellow gold. 

Introduced by Iowa State University, ‘Sunrise’ is an excellent cultivar for southern and central Iowa.  Its flower buds are hardy to - 20 degrees F.  Plants are covered with masses of small, medium yellow flowers in early spring. ‘Sunrise’ is a semi-spreading, compact shrub with a mature height and width of 5 feet.  Its compact size makes ‘Sunrise’ ideal for small hedges or shrub borders. 

Other suitable cultivars for Iowa include ‘Northern Gold’ and ‘New Hampshire Gold.’ 

Should I fertilize my June-bearing strawberries in spring? 

Established plantings of June-bearing strawberries should not be fertilized in spring. Spring fertilization stimulates foliar growth, produces softer berries and increases disease problems.  Lush, vegetative growth may make picking difficult. Also, soft berries are more likely to be attacked by fruit rots. As a result, a spring fertilizer application may actually reduce the fruit yield. 

Fertilizer should be applied to June-bearing strawberries during the renovation process immediately after the last harvest of the season. Apply approximately 5 pounds of 10-10-10 or a similar analysis fertilizer per 100 feet of row. 

When is the best time to divide hostas? 

Spring is the best time to divide hostas. Dig up the entire clump as soon as the leaves begin to emerge. (The emerging leaves are bullet-shaped and are often referred to as “points” or “noses.”)  Carefully divide the clump into sections with a sharp knife. Each section should have at least two or three points (leaves) and a good portion of the crown and root system. Replant immediately. 

While spring is the best time, hostas can be divided anytime from spring to late summer. Hostas divided in late summer should be mulched with several inches of straw, pine needles or other materials in late fall. Mulching helps prevent repeated freezing and thawing of the soil during the winter months that could heave late summer divisions up out of the soil and damage or destroy them. 


There is one photo available for this week's column.