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Feehan: Fall flower care tips

October 27, 2017 GMT

A late fall freeze allowed chrysanthemums and other fall-blooming perennials to reach their full glory. Correct fall care of perennials and roses will send them into winter better prepared to survive.

For fall care of mums and roses, maintain a moist, but not wet, soil well into fall. Well into fall means up until the soil begins to freeze, which is typically in late November.

Due to cooler temperatures and fall rains, autumn irrigation may not be needed. If needed, fall watering can be very beneficial for plant survival over winter and performance next season. This is especially true for fall-planted perennials and new and established roses.

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While a consistently moist soil is important to plant performance and winter survival, avoid overwatering. Perennial flowers are susceptible to root and crown rots if the soil remains too wet. Wet fall and winter soils also increase the risk of winter kill.

Check the soil before watering. If it is moist, there is no need to irrigate. If it is dry, the plant will benefit from irrigation even if the plant is dormant and freeze-killed tops have been cut back. Roots continue to grow and function until soil temperatures drop below 40 degrees.

Questions about when to cut back the freeze-killed tops of perennials and when to prune roses — fall or spring — are common at this time of year.

For most perennial flowers, it is recommended to wait until the tops die back naturally or are killed by a hard freeze. If a perennial has winter interest, and was not infected by a disease this past summer, it is fine to wait until early spring to cut tops back.

Peonies and chrysanthemums are the exception to this rule. Peonies can be cut back any time after Sept. 1. Winter hardiness of chrysanthemums varies and even hardy mums may not consistently overwinter in Nebraska. Studies have indicated that leaving the tops of mums over winter can increase winter survival.

As a rule, wait until late April to prune roses. However, hybrid tea, grandiflora, floribunda and some miniature rose cultivars need winter protection. These types of roses may need some pruning now to fit beneath a protection method, such as a rose cone; or to remove tall lateral canes that may be damaged by winter winds.

Since the majority of rose pruning should be done in April, only prune the amount needed for the rose to fit beneath the protection method or to cut back tall laterals. Wait until spring to do the majority of pruning.

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As for winter protection for mums, other tender perennials and roses, wait until the soil has frozen or night temperatures are consistently dropping into the 20s to put winter protection in place. If applied before the plant is fully dormant, this can delay dormancy and increase cold-temperature injury.

Use a loose mulch such as shredded wood, large tree leaves or straw. Loose mulch placed about 1 foot deep over the tops of tender perennials and roses after the soil begins to freeze maintains a consistent temperature around plant crowns and reduces winter drying, which is a common winter killer of plants.

Winter mulch also prevents soils from freezing and thawing over winter. This action causes soils to heave and damages roots or uproot plants. Preventing this is especially important for fall-planted perennials that do not have a well-established root system.

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