What's Up In The Garden by Jackie Dohlman, Franklin County Master Gardener

 Tips on Fire Blight in Crabapples, Late Emerging Perennials, and Planting Tuberous Begonias

Several new shoots on my crabapple have turned brown and wilted. What is the problem?

Fire blight probably is responsible for the wilted shoots on your crabapple. Fire blight is caused by the bacterium Erwinia amylovora. Plants susceptible to fire blight include apple, crabapple, pear, hawthorn and cotoneaster.

Symptoms of fire blight appear in spring within a few weeks of bloom. Succulent, new shoots turn dark brown to black and wilt. The wilted shoots somewhat resemble the top of a shepherd’s crook or candy cane. Small droplets of amber-colored bacterial ooze can often be seen on blighted shoots when the weather is warm and humid. Under favorable environmental conditions, shoot infections may continue to move down the branches and kill large portions of the tree.

The best way to avoid fire blight is to select crabapple, apple and pear varieties that are resistant to the disease. Also, avoid heavy pruning and fertilization that promote excessive shoot growth. Succulent, rapidly growing shoots are more susceptible to fire blight infections.

In spring and early summer, periodically inspect susceptible plants for symptoms of fire blight. Promptly remove infected shoots. Several precautions should be exercised when pruning in spring and summer. Never prune during wet weather. Make pruning cuts eight to 12 inches below diseased areas. Finally, disinfect pruning tools in a 10 percent bleach solution (one part household bleach to nine parts water) or 70 percent alcohol after each cut to prevent spreading the disease.

It’s early May, but I don’t see any signs of my balloon flowers. Should I be worried?

Don’t worry. The balloon flower (Platycodon grandiflorus) is slow to emerge in spring. Other late emerging perennials include hardy hibiscus (Hibiscus hybrids), butterfly weed (Asclepias tuberosa), and Russian sage (Perovskia atriplicifolia). It’s a good practice to mark the locations of late emerging perennials to prevent damaging these plants when working in the garden in early spring.

When can I plant tuberous begonias outdoors?

Plant tuberous begonias outdoors after the danger of frost is past. In central Iowa, mid-May is an appropriate planting date. Tuberous begonias perform best in moist, well-drained soils in partial shade. Choose a site sheltered from strong winds. In the home landscape, sites that receive morning sun and afternoon shade are often excellent planting sites. Use a well-drained potting mix when planting tuberous begonias in window boxes, hanging baskets, and other containers. When planting tuberous begonias, place the plants at the same depth they grew in the container. Planting them deeper than previously grown may encourage the buried portion of the stem to rot.

Once planted, watering, fertilizing and deadheading are the primary maintenance chores. Tuberous begonias should be watered weekly in beds and borders in dry weather. Plants in containers will have to be watered more often. Check container-grown plants regularly (daily or every other day) and water as needed. Fertilize tuberous begonias every two to four weeks with a dilute fertilizer solution. Remove spent flowers to improve their appearance and encourage additional blooms

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