Watering, soil tests and the start of winter

  • Have your garden soil tested to determine what fertilizers to use.

    Have your garden soil tested to determine what fertilizers to use. Courtesy of Chicago Botanic Garden

By Tim Johnson
Chicago Botanic Garden
Posted12/5/2021 7:00 AM

Evergreens planted over the last couple of years may need to be watered again this season if conditions are dry. It is easy to forget about watering during the colder weather in November and early December.

Recently planted evergreens should not go into winter under stress from being too dry, which increases the chance of winter burn. More attention should be given to trees planted in sandy soil. Evergreens can lose moisture from their leaves faster than the roots can replace it from frozen ground when there is low soil moisture, freezing temperatures and blowing wind.


Make sure the root balls of evergreen trees are thoroughly moistened when watering by applying water to the base of the plant. Densely branched evergreen trees can shed water from rain or a sprinkler away from the root ball.

• Have your garden soil tested to determine how best to manage it and what fertilizers to use. Make a composite sample from a few areas in the bed and send in for testing. If your garden is large, it is a good idea to break the garden into zones to test.

Soils in the Chicago area tend to have adequate phosphorus levels, so choose fertilizers that have little or no phosphorus in them. A soil test will confirm the makeup of your garden soil.

• Winterize your hybrid roses after there have been two to three hard freezes (temperatures in the teens), which typically occur in late November at the Chicago Botanic Garden.

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Cut back rose canes to about 18 inches and mound the roses with 12 to 15 inches of compost or mulch for the winter. Do not use grass clippings, which will mat down and hold moisture around the plants.

It is best to clean up and remove any rose leaves that have fallen if you had problems with black spot, which is a common fungal disease. This disease will overwinter on infected foliage. Shrub roses do not require this special treatment for the winter.

• Clean out your gutters once all leaves have fallen. Leaves can clog up gutters and are very difficult to remove if frozen in. Leaf fall is later than in normal years, so watch the weather forecast as you monitor your trees.

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

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