When Do I Remove Mulch From Perennials in Spring?

My picture shows Ruby Frost coreopsis. It's a bi-colored flower with a rich red color.
'Ruby Frost' is a bicolored cultivar of the perennial, coreopsis. David Beaulieu

Some gardeners wonder, "When do I remove mulch from perennials in spring? Or should I just let them push up through it on their own?" In order to answer that question in depth, we will have to step back a bit to review why we mulched these plants in the first place. But a short, general answer can be provided immediately:

If the mulch that you applied in fall consists of a coarse material, such as large, unshredded leaves, or if the mulch that you are using tends to mat down over time and form a barrier, then you should generally be removing that layer of mulch in spring at a time when the threat of severe cold has passed.

Tips on Mulching Perennials

If you are going to mulch plants in the fall, wait to do so until the soil has frozen. Generally speaking (and this will vary depending on a number of factors), apply a layer that is about 4 inches thick. Here are two of the reasons that the experts often give for mulching perennials:

  1. Mulch supplies perennials with an insulating blanket that helps you "put them to bed" for the winter. Resting under the blanket of mulch, plants will not be tempted to wake up during premature warming periods and put out growth that would only be damaged when cold weather returns.
  2. Drawing again on the principle of mulch being used as an insulator, gardeners attempting to grow a perennial that is considered cold-sensitive (or "borderline-hardy") in their region may be able to overwinter it with the help of a protective layer of mulch.

Reason #1 will be persuasive to those gardeners living in areas subject to great swings in temperature.

For example, some regions have long, cold winters that may, nonetheless, experience sudden thaws (after which winter returns with a vengeance). If you garden in such a place, you do not want your perennials being tricked into emerging from their sleep during one of these false starts; doing so would only expose them to danger.

Mulch will also help prevent damage that may occur due to heaving during freeze-thaw cycles.

Reason #2 affords a good reminder as to why it is important to research the plants that you are growing (or that you intend to grow). Some types of Coreopsis, for example, are very cold-hardy, while others are less so and may need the extra insulation given by a layer of mulch to survive the winter in your location.

Do note, however, that mulch is not always necessary for perennials. Here are some of the scenarios in which you may be able to get away with not mulching:

  1. The plants in question are very cold-hardy.
  2. The plants are well-established.
  3. Your region is not subject to great swings in temperature during the off-season for gardening.

Moreover, perennials prone to crown rot (for example, delphinium) often die off during the winter not from extreme cold but from excessive moisture. What they most need to survive the winter is not insulation, but good drainage. In fact, since mulch helps the soil retain moisture, it may actually be counterproductive for such plants if it is piled up over their crowns.

When to Take Mulch Off Perennials: the Long Answer

To a large degree, getting the timing right for mulch removal requires you to be observant regarding your plants and the weather conditions where you live.

If your memory is not good, it helps to keep a garden journal from year to year.

But, after a while, all of this should become second nature for you. You will know when spring is "here for good" in your region, and you will know when your perennials are really supposed to be pushing up new growth for the year. When, based on past observations, the time has come for spring to wrest control from winter (that is, the chance of suffering a hard frost has passed) and for a particular perennial to emerge from its slumber, you should begin checking to see whether the ground is thawing or not. If the ground is thawing, leaving landscaping mulch on top of your perennial flowers can smother them or invite harmful molds -- so it is time to remove the mulch, to let your perennials breathe.

While perennials sometimes will successfully break through a barrier of mulch, other times damage will result.

Don't take a chance with the health of your perennial flowers!

Even if a covering of mulch does not completely smother a plant, it can, at the very least, disfigure its leaves. Part of the beauty of a plant is its foliage and stems (vegetation). If the vegetation has to struggle to push up through a layer of coarse mulch, doing so may take a toll on the appearance of its vegetation, initially. While no permanent harm is done, this does temporarily mar the visual display for you. Since enjoying the visual display to the fullest is the reason why you are growing the plant, this is not an unimportant consideration.

Once the perennial flowers have pushed up and have achieved a bit of height, then you can re-apply garden mulch around them to suppress weeds. Shredded leaves make for an excellent mulch because they are light and fluffy; they break down readily and -- when they do so -- release valuable nutrients into the soil.