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posted: 10/12/2013 1:00 AM

Wait until spring to divide hardy mums

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By Mary Boldan

Q. I have hardy mums that bloom in the late summer and early fall. Is it OK to divide them once they have finished blooming in the fall?

A. Don't be tempted to divide your mums in the fall. They respond best to being split in the spring, just as they're starting to grow. After the last spring frost when shoots are 1 to 3 inches tall, dig them up and carefully pull or cut them apart. Discard half-dead or overly woody parts, and plant only the healthy divisions.

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It is a good practice to divide mums at least every two to three years in order to rejuvenate them and promote maximum flowering. Mums can withstand very cool temperatures and even light frosts. The first hard frost usually marks the end of the season for hardy mums. Once the plants are dormant, remove the tops, clean up old leaves and debris and re-mulch the area. New shoots will appear early the following spring.

Q. I noticed my neighbor applying mulch to many of the perennials in his garden. I remember reading somewhere that you should not apply mulch too early. Is that true? Why?

A. Mulch is used year round to keep soils evenly moist and to reduce weeding. It also keeps the soil and crowns from drying out by winter winds. Additional mulches can be applied for winter protection after the ground freezes and remains frozen. This occurs when nighttime temperatures drop to the teens for several nights in a row. The object is not to keep the ground from freezing, but to keep it from thawing and refreezing repeatedly. Mulch added to frozen ground insulates the soil and keeps the ground evenly frozen until the final spring thaw. In the Chicago area we often have repeated freeze/thaw periods in January and February. During these periods, plant crowns and roots can be heaved upward exposing tender roots to killing temperatures. Frost heaving most often happens in low spots in the soil where water accumulates and ice forms. A level bed with no depressions is less susceptible to frost heaving.

Roses

The best method for mulching roses in Northern Illinois is to "hill up" 10-12 inches of well-drained loose soil/compost mix around the base of the plants. If you grow hybrid tea roses you need to protect the graft union (planted two to three inches below soil level in our climate) from winter damage. After the mound freezes you can pile on straw, evergreen boughs, or loosely packed leaves to keep the ground frozen and insulated. To keep soil and mulch in place during the winter, you may want to encircle each bush (18-24 inches diameter) by chicken wire forming a cage 18 inches high. After the spring thaw you can gently dig the mulch into the soil around the bushes. Be careful not to damage the root system when you do this.

You could also place styrofoam cones over your roses. If you choose to do this, make sure you poke at least 4, 1-inch holes around the top of each cone to release heat and provide good aeration inside the cone. For best protection you should mound soil over the crown of the plant before you put the cone in place. Put a brick on top of the cone to keep if from blowing away.

Perennials

Evergreen boughs are one of the best mulches for most perennial beds. Some gardeners successfully use three to four inches of leaves piled loosely over the plants. This method is not as effective as evergreen boughs because the wet leaves could become matted and lead to crown rot of the plants. Additionally, because piles of leaves provide good insulation, they can make attractive winter homes for mice and other small rodents.

Gently remove the mulch in spring when nighttime temperatures are no lower than freezing, usually mid-late April in this area. Be careful not to damage emerging plants when you remove the mulch. A leaf blower is a good way to remove mulch from around plants if you used leaves.

Q. When it comes to gardening, what is the difference between a frost and a freeze?

A. According to the National Weather Service (NWS), frost is when the temperature of the Earth's surface falls below 32 degrees. This forms thin ice crystals that can cover the ground. Since a frost is temporary, you can protect your plants by covering them or bringing them indoors the night the frost is predicted. On the other hand, a freeze is when the temperature is expected to remain under 32 degrees for an extended period of time A freeze generally spells the end of the growing season for tender plants.

• Provided by Mary Boldan, Master Gardener Answer Desk, located at Friendship Park Conservatory, 395 Algonquin, Des Plaines, is open 9 a.m. to noon on Wednesdays. Call (847) 298-3502 or email Cookcountymg.com@gmail.com

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