Rx for Summer Tree Care

Taking Care Of Trees And Other Plants After Unusually Wet Weather

LISLE, IL (July 1, 2008) – April showers can bring May flowers, and summer fungal diseases. Given the wet spring we just finished, your garden may be experiencing problems. Follow The Morton Arboretum guidelines for tree and shrub care after excessive moisture.

Watch out for anthracnose, which commonly occurs after wet weather. Spores from several kinds of fungi infect newly-grown leaves. Symptoms include brown or black blotchy areas on the leaves. While this will not kill your tree, it is important to discard fallen leaves to prevent re-infection.

“Since fungus needs wet weather to infect, a few things you can do to prevent fungal infections are to avoid overhead watering and if a plant is very dense, you could thin it so it would dry faster after rainfall, ” says Donna Danielson, Arboretum Plant Clinic Assistant.

There are some fungicides on the market, but once a tree is infected, it is too late to spray a fungicide. They should be applied as leaves are emerging.

Some trees are sporting yellowing leaves. A possible culprit is too much soil moisture. This occurs when the roots are not able to dry out in between watering. Too much water can often be more harmful to a tree than not enough water.

How wet has it been? The average rainfall (from 1937-2007) at the Arboretum between April 1 and June 30 is 11.4 inches. This year we had 15.02 inches in the same time frame, according to Plant Clinic records.

As the summer heats up, look out for leaf scorch. "Leaf scorch is a condition and not a cause. The culprits include unfavorable weather conditions such as high winds, drought or soils that are too wet, root damage from compacted soil, grade changes, and restricted root growth," says Doris Taylor, Arboretum Plant Information Specialist.

Symptoms, usually appearing in July and August, consist of browning on the tips of leaf tips and yellowing between leaf veins and leaf margins.

To minimize leaf scorch, give your tree or plant a break. “Place trees in well-drained soil with adequate root space, water well in dry periods and conserve moisture with a 3-4" depth of organic mulch,” Taylor says.

For more hot weather advice, Taylor offers the following tips:

• Keep on top of weeding, especially after the rainy season. Weeds that go to seed will be a bigger problem next year.
• Cut back rampant growth on aggressive plants that may be smothering neighboring plants and prune back spring perennials that are going dormant, such as bleeding hearts and oriental poppies.
• Trim spent flowers, also referred to as deadheading, on perennials and annuals, to encourage a second flush of flowers.
• Keep watering your garden when there has not been adequate rainfall. This is especially important for any newly-planted trees and shrubs whose root systems are not fully developed.

While caring for the garden this summer, start thinking ahead to next year. Photograph your yard each month and note where you could use more bulbs or color, or where plants are not staying healthy. This will make it easier in the wintertime when you plan improvements in your garden’s health and beauty.

Homeowners with questions on tree and other plant care or selection can visit the Plant Clinic page on the Arboretum website, www.mortonarb.org; visit the Plant clinic, open 10 a.m. – 4 p.m. Monday – Saturday; call the clinic at 630-719-2424 or email the experts there at This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Services are free of charge.

The Morton Arboretum is an internationally recognized 1,700-acre outdoor museum with collections of 4,117 kinds of trees, shrubs, and other plants from around the world. The Arboretum's beautiful natural landscapes, gardens, research and education programs, and year-round family activities support it s mission – the planting and conservation of trees and other plants for a greener, healthier, and more beautiful world. Conveniently located at I-88 and Rte. 53 in Lisle, Illinois, the Arboretum is open 7 days a week, 365 days a year, from 7 a.m. to 7 p.m. Central Time or sunset, whichever is earlier. The Children's Garden is open from 9:30 a.m. to 5 p.m., March through October, and 9:30 a.m. to 4 p.m., November through February. Visit www.mortonarb.org or call 630-968-0074 to learn more.

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