Check for drought stress on trees and plants

Have you noticed the effects of our extended dry conditions on your trees and plants? I recently started watering some established plants (including some large oak trees) in my home garden because of the signs of drought stress. Drought stress signs include leaves that are wilting and off-green colored leaves. As the leaves start to show fall color, it becomes more difficult to recognize drought stress. Lots of my hydrangeas had leaves turning brown and dropping off well before the normal time to drop.

Bulb placement

Proper placement is important for success with spring-flowering bulbs. They prefer moisture in early spring and fall and dry conditions in the summer when they are dormant. They do not usually perform well in wet sites or in heavy clay soil. If your garden soil has a lot of clay, plant bulbs higher than recommended. In general, plant bulbs at three times the diameter of the bulb if there are no directions included with your bulb purchase. Most large bulbs should be planted around 6 inches deep, with small bulbs planted around 4 inches deep.

Beware of limestone near plants

Avoid using gravel with crushed limestone for the base of hardscape features such as walks, driveways and patios. Limestone increases the alkalinity of adjacent soils and makes growing some plants more difficult if they are planted close to the limestone base. Plants such as witch hazel and river birch that are sensitive to alkaline soil conditions become chlorotic as their roots grow into the limestone base. There are alternate materials — such as grade 9 gravel — that include fines (the smallest crushed particles) for compaction to use for the base of hardscapes.

Pros and cons of crocuses

Crocuses are ideal bulbs for naturalizing, rock gardens or underplanting beneath tall trees. They may be scattered in lawns, but their grasslike foliage must remain intact for at least six weeks before being mowed to a short height for the best long-term results.

Crocuses, which are planted at a shallow depth, are easy targets for chipmunks and squirrels and might require repellent products or light chicken wire screening placed directly over them at planting time. Blood meal sprinkled on the ground after planting may help deter animals from digging up newly planted bulbs. There are also granular repellents available to spread over planted areas.

Chipmunks and squirrels tend to be attracted to beds that are freshly dug. After having a new planting of 500 crocus dug up and eaten this spring, I have switched to planting glory-of-the-snow (Chionodoxa) in hopes the chipmunks and squirrels will be less interested.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.