Illinois gardeners live in the middle of rose country as well as in the middle of the United States. U.S. Department of Agriculture (USDA) plant hardiness zones 5a through 7a cross the state, making the state’s gardens friendly for many kinds of roses (Rosa spp.), which are hardy in USDA zones 4 through 10. All Illinois roses, though, need protection through winter dormancy, and that protection must be removed in early spring.
The growing season in Illinois varies from 160 days long in the north to 190 days long in the south, ending in hard freezes followed by several months of cold weather. The end of the growing season begins as early as Aug. 28 in the northwest in Carroll County to Nov. 1 through 10 or later in southern counties. In spring, last frost dates range from early March to the end of May. In terms of frost dates, the urban heat island in the state's northeastern portion has more in common with the southern part of the state than with the suburbs that surround it.
Several protection methods help roses survive extreme cold as well as the ups and downs of temperature, precipitation and wind of Midwestern winters. Whether a cocoon of compost and leaves or a foam rose cone is used for each rose, the goal is to protect the plants from extremes, particularly when no insulating snow is on the ground. In spring, before temperatures moderate, winter protection can convert to a cooker as the sun rises in the sky. Although compost and leaves allow some ventilation, foam cones trap heat. Both methods build heat, encouraging early development of tender buds that might be nipped by a late frost after the rose plants are uncovered.
Start checking for new branch buds on covered roses one month before the last annual frost date in your area, or sooner if the weather has been warm and sunny. If no buds show on a buried rose bush, just recover most of it, and discard about one-third of the mulch. Uncover cone-covered rose plants as soon as the weather warms within one week of the last frost date to avoid cooking them. Uncover roses as soon as buds begin to appear to harden off the plants. Allowing buds to form and growth to begin while the plants are covered will result in weak growth that dies.
Once buds begin to form, they need to harden off. If weather warms early or a stretch of sunny days warms the soil, remove the plants' protective mounds gradually until buds form. Pruning tender hybrid tea roses at or near the last frost date removes winter die-off and encourages the shrubs to produce new canes or branches. Hardy shrub roses tolerate earlier exposure and heavier pruning; they need heavy pruning because they grow so fast. Complete pruning just as buds begin to form. No matter what type of roses grow in your Illinois garden, try to have them uncovered and pruned on or before the last average frost date in your part of the state.
- Illinois State Water Survey, State Climatologist Office for Illinois: New U.S. Department of Agriculture Plant Hardiness Zone Map
- Illinois State Water Survey, State Climatologist Office for Illinois: Illinois Frost Dates and Growing Season
- American Rose Society: Winterizing Roses in the North Central District
- David Austin Roses: Roses for Hot Zones, Cold Zones -- Climate Information
- University of Illinois Extension: Our Rose Garden -- Winter Protection
- Chicago Botanic Garden: Spring Rose Care
- My Chicago Botanic Garden: Time to Uncover the Rose Garden
- University of Illinois Extension: Springtime is Rose Time
- Star Roses and Plants/Conard-Pyle: How to Care for a Knock Out Rose
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