How should I handle watering my new garden this fall? Can I stop watering now that plants are beginning to go dormant? I am starting to see some fall color.
— Patrick Bell, Algonquin
I am writing this column at the beginning of fall on a day with temperatures above 80 degrees Fahrenheit. While I am enjoying the wonderful late touch of summer, I am also concerned about the dry conditions in the garden. Homeowners with new gardens need to pay more attention to watering over the first couple of years, including throughout the fall. New plantings need routine monitoring even when there is a sprinkler system. A sprinkler system using mist heads may not deliver enough water to trees and shrubs that were balled and burlapped at planting. You may need to supplement a sprinkler system with spot watering by hose at the base of the plants. Watch for wilting plants as a sign that more water is needed. I have been seeing more systems with drip irrigation used for trees and shrubs, which should work well. Without adequate rain, the dry conditions will still be a concern later in the fall, even as temperatures decline. Plants may still be under drought stress when the weather is cooler, and plants are starting to go dormant. It is easy to forget about watering in the cool weather and dry plants that are under stress are not as easy to spot. In terms of watering your garden, be sure to consider such variables as the type of soil in your garden, types of plants and when the plants were installed. Other considerations include rainfall as well as how much you watered during the past summer.
In general, focus your watering efforts on trees and shrubs that were planted this year, with attention also given to plantings done over the last two to three years. Less established plant material (especially recently installed plants) suffer damage much more quickly than your older plants. Evergreens planted over the last three years will be more likely to suffer winter burn if they go into winter under stress from dry conditions. Be sure to apply water to the base of evergreens to get the root ball moistened. The foliage of evergreens can shed water from a sprinkler to the outside of the root ball, leaving it dry. As the tree becomes established over the first two to three years, the roots will grow out into the surrounding garden soil. Keep watering these evergreens into November if dry and warm conditions persist.
Finally, turn your efforts to established trees and shrubs. Water the soil to a depth of 8 to 12 inches. If watering from overhead, try placing an empty cup or can next to the plant and watering until the container holds 1 to 1 1/2 inches of water. Adjust watering as needed as it rains. Long, slow, soaking rains are great, but there can be a lot of runoff when there are short, heavy rains. Be sure to check your soil if you are unsure whether to water more. We started watering our mature oak trees and other wilting plants at the end of September after the extended dry period.
It’s getting too late to seed grass, but if you do, keep the grass seed moist with frequent light watering until it germinates. An extended period of late warm weather will benefit seeding and increase your chances of success. Sod can be installed until the ground freezes. A night of freezing temperatures can freeze the rolls of sod before the ground freezes and make installation impossible until they thaw out. New sod needs less frequent but deep watering every two to three days, depending on the weather, until it starts to grow. Then you can switch to a routine irrigation program.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.