Mulch Perennials and Bulbs after the Soil Freezes

By Katie Drewitz

While I continue to hope for nice autumn weather, we know that winter will come in the next few weeks. As the soil freezes, we need to be thinking about mulching both perennial and bulb flower beds.

Although snow is the best winter protection for perennials, we can’t always depend on adequate snowfall to form sufficient insulation. Therefore, protective cover mulch is recommended to protect plants from extreme cold.  More importantly, it prevents fluctuating temperatures and early spring warmups from bringing plants out of dormancy at a time when they may be vulnerable to damage by cold temperatures.  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.  

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, or any time after that point. 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 ultimately weaken the plants.  

Useful and effective mulches for perennials and bulbs include: five or six inches of whole or shredded leaves, partially decomposed compost, ground corn stalks and straw.  Although wood chips 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. 

If you have questions about this or any other horticulture, agriculture or natural resources  topic, please reach out to your local Extension educator. Residents in Fillmore and Houston counties can call 507- 765-3896 or 507-725-5807.  

Katie Drewitz is the University   of Minnesota Extension Agriculture, Production, Horticulture & Natural Resources educator for Fillmore and Houston Counties.