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Mulch Perennials and Bulbs after the Soil Freezes
by Randy Nelson, November 13, 2008
Articles & Publications   

The recent drop in temperature that occurred late last week and continues to persist reminds us that it is time to cut back our perennials and spread a layer of cover mulch over them and our bulb beds.

Although snow is probably the best winter protection for perennials, we can not always depend on adequate snowfall to form adequate insulation. Therefore, protective cover mulch is applied to protect plants from extreme cold.  More importantly, it prevents fluctuating temperatures and early warm ups from bringing plants out of dormancy at a time when they may be vulnerable to damage by cold weather.  The alternating freezing and thawing that may occur will also cause the plants to be lifted, or heaved, out of the soil, which will destroy the roots of many plants and kill them.  In the case of spring flowering bulbs, mulch applied after the soil has begun to freeze will prevent them from emerging too early in the spring when they may be damaged by late freezes.

The recommended time to apply protective mulch is as soon as the soil begins to freeze, but it can be applied long after that.  In fact, mulches can be applied on top of the snow and the snow will increase the insulating value of the mulch.  It is very tempting to apply the cover mulch when we are cleaning up the gardens in the fall, but it is very important not to apply the mulch to perennials before the soil begins to freeze as this may encourage growth beneath the mulch that will weaken the plants. 

Frozen ground will also protect your plants from the feeding activity of mice and voles that may use the mulch as a winter home.  To further protect your bulbs and plants from rodent damage, place some bait stations made from beverage cans, PVC pipe, tin cans or similar receptacles in which you have placed a tablespoon of a pelleted rat and mouse bait beneath the mulch.  It is important to remove these bait stations as soon as the snow melts in the spring so that they are not picked up by children or come in contact with pets.

Useful and effective mulches include five or six inches of whole or shredded leaves, partially decomposed compost, marsh hay, ground cornstalks, pine needles, straw, and evergreen boughs.  Although woodchips and shredded bark are excellent mulches, they are better used for covering the soil between plants where it can be left undisturbed throughout the year.  Remove the mulch as it thaws in early spring to avoid crown rot and other fungus problems.  It is wise to keep the cover handy in case of a late spring freeze.

Newly planted trees and shrubs should already be mulched with woodchips or shredded bark to keep the soil from freezing as early as bare soil.  Early mulches around woody plants allow you to continue to water later in the season.  Late season watering is important, particularly in the case of evergreens.  It is critical that evergreens go into dormancy without suffering from moisture stress since they will continue to lose moisture through their needles throughout the winter.  If you have not mulched newly planted trees and shrubs do so now. 

Source: Carl Hoffman, Extension Educator, Stearns and Benton Counties.

If you have questions regarding this article or ideas for future articles please call the Clay County Extension office at 218.299.5020, 1.800.299.5020 or email me at nels1657@umn.edu.  More information on horticultural or agricultural topics can be found by visiting the Extension, Clay County web site.

The University of Minnesota, including the University of Minnesota Extension is an equal opportunity educator and employer.

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Last updated February 05, 2010.