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Hydrangeas

When is the best time to cut back hydrangeas? How far do I cut them back?

Pruning hydrangeas depends on the species. Oakleaf hydrangea (H. quercifolia) and Peegee hydrangea (H. paniculata), with its well-known cultivars ‘Limelight’ ‘Little Lamb’ and ‘Tardiva’, are woody shrubs that bloom on old wood. Trim them within two to three weeks after flowering. The following year’s primary flower buds form near the top of the stems in late summer. If you wait too long to prune, you will be cutting off flowers on the old stems.

The new bigleaf hydrangea (H. macrophylla) ‘Endless Summer’ is an herbaceous plant that dies to the ground over winter and starts into new growth in spring. It can be cut at any time since it flowers on both old and new wood.

Hydrangea ‘Annabelle’ (H. arborescens) can be trimmed at any time. “It dies back totally to the ground each year so you can keep it trimmed to the size you want,” says Jean Bragdon, garden center manager at Lurvey’s Garden Center, Des Plaines.


Planting Tulips

Is there a best time to plant tulips? I see them at the garden centers in late summer but I am afraid that it is too early to plant them. If I wait too long, I might forget all about them.

Fall bulb planting should wait until soil temperatures drop to 55 degrees or cooler. This usually occurs when nighttime temperatures drop to 50 degrees or lower for two weeks or more. While waiting to plant, store the tulips in a cool, dark place away from direct sunlight—but don’t forget them. After planting, water the bulbs well, advises the Netherlands Flower Bulb Information Center.

If you plant grape hyacinth bulbs amidst your tulips, they will come up early in the fall and serve to mark the position of your tulips.


I've got green worms!

What is the green worm that eats my roses and columbine every year?

It is hard to diagnose your problem without seeing the caterpillar. There are several green worms that bother roses, and one can be controlled with Bt (Bacillus thuringiensis) but rose slug, for example, cannot. Proper identification is necessary before applying any control method. Do not use an insecticide for anything that"s not on on the product label. Do not use any insecticide as a preventive measure. It doesn"t work and ends up being harmful to the environment and a waste of your money.

Green worm on your columbine could be an inch worm or canker worm. If the caterpillar loops up in the center or arches as it moves along, it could be a looper or cabbage worm. Leaf miners, which are usually white or pink, tunnel in the leaves. “To eliminate insects, use insecticidal soap,” said Nancy Clifton, Chicago Botanic Garden Plant Information Specialist.

For an exact diagnosis, consult your local University of Illinois Extension service or collect a specimen and bring it to the Plant Information Service at the Chicago Botanic Garden or the Morton Arboretum.


Japanese Red Maple

I have a nicely sheltered, rounded 7-foot tall Japanese red maple on the southeast corner of my backyard. Half of the tree has lost its leaves, the formerly red bark is turning gray, and a good-sized square of bark has been stripped off on the side that faces the yard. I sprayed the exposed bark with black pruning spray to close any entry for insects. I have not cut off any of the branches.

Does the winter have any effect on the tree? Should I look for some insect infestation? What should I do now?

“It appears that the tree suffered some kind of injury. Over winter, watch for sun scald on the southern exposure. Use paper tree wrap on the trunk,” advises Mike Geimer, owner of Geimer Greenhouse, Long Grove. If you are fearful of insects, you can use an organic pyrethrum spray. Black pruning spray is not necessary.


Slugs

I am sick of slugs. Perhaps if I knew their life cycle I could get rid of them. Where do they go over winter? Where do they come from? What is the best way to get rid of them?

Slugs are gastropods belonging to the mollusk class. They have lungs and can breathe air and live one year. At nightime, to conserve moisture, they feed by biting tissue with a rasping mouth underneath their body. They move by sliding over slime secreted by a large muscular foot and constantly lose water from this slime production and evaporation.

To make matters worse, they are hermaphrodites having both male and female organs and can deposit egg-like clusters of 1/8 inch pearls in soil where they overwinter. Their growth is activated by rising soil humidity and temperature in the spring, according to Ed Valauskas, Manager of Library and Plant Information Services at the Chicago Botanic Garden.

Even if your soil is relatively slug free, they can come in from a neighbor’s yard or live in the soil of container-grown plants. If you garden in very sandy, fast draining soil, you will probably not have many of these pests, but in heavy clay soil, slugs find constant moisture that suits their life style.

Slugs feed on plants with moisture in them, especially hosta, ligularia, dahlia and begonia leaves, lettuce, strawberries and tomatoes. They hide by day and feed at night or on gray, damp days. Go outside with a flashlight after 10 p.m. and look for them under boards, rocks or pots and destroy them.

Laurie Skrzenta of Laurie’s Landscape, a Downers Grove hosta grower, keeps the hosta area dry and doesn’t water them because slugs do not live in dry locations. She depends on rainfall and maintains that hostas can exist without supplemental water. Laurie also suggested using coarse sand as a mulch. Another possibility is to sprinkle sand in the center of your dormant hostas since this is where the slugs lay their eggs.

There are many home remedies to get rid of slugs including beer, ammonia water, ice water, and yeast water. Gardener Anna Hevrdejs, Woodridge, suggests sprinkling corn meal around slug areas. Slugs like to eat it, then die. Replace it after a rain. She also claims that sweet woodruff planted around hostas restrains the slug population.

Chemical metaldehyde or methiocarb pellets are useful but they can be attractive to dogs and children. They are very toxic. Much safer is a copper strip laid around the areas to be protected, although this is not practical in an ornamental garden.


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