Mulching perennials helps them survive winter

Mulch use

Protecting your perennials over winter requires mulching. Mulching perennials helps to protect the overwintering perennial roots from the effects due freezing and thawing of the soil that occurs during the winter season.

Winter in Northwest Ohio has warm days above freezing and severe cold that may drop below 0 degrees Fahrenheit. Like ice cubes when water freezes turning into ice, the freezing water causes the cubes to expand. Likewise, when the ice cubes melt, the ice and water contracts.

Moisture in the soil during the winter behaves similarly to ice cubes. Freezing and thawing of the soil breaks up the roots of the perennials and could potentially kill the perennials altogether. Mulching perennials helps to maintain a consistent soil temperature in the soil.

What type of mulch is best for overwintering perennials? The best type is often the same mulch that is used during the summer — comprised of organic material. Organic mulch is derived from once living, plant-based products.

During the summer organic mulches decompose over time. As they do, they settle reducing the depth of the mulch layer, thus increasing the organic matter in the soil. The decomposing process is accomplished by bacteria that live in the soil; however, during the winter the bacteria goes dormant, and the mulch normally does not decompose.

The reason why some mulches decay faster than others at the same given depth during the summer is that some mulches contain lignin. Lignin is part of organic matter that resists decay. Some mulch contains more lignin than others. Try to avoid mulches high in lignin. Some mulches high in lignin include Oak leaves, pine needles and pallet wood.

Other mulches to avoid are derived from walnut species, most notably Black Walnut (Juglans nigra). Black Walnut, as well as other walnuts, produce a naturally occurring herbicide called Juglone. Juglone is found in the wood, roots and leaves. In general, juglone not only inhibits seed germination but is often toxic to established woody plants and perennials.

When selecting a mulch, consider not only cost and color, but also natural origin. There are so many choices. Common organic mulch choices include cypress, hardwood and leaves. Cypress mulch is harvested from the cypress trees in the swamp areas of the South. One of the reasons these trees can grow in flooded conditions is that their wood repels water. Cypress mulch is ideal for use around walkways and driveways, but not flowers or vegetable gardens, because of the tendency to repel water away from landscape plants.

Hardwood mulch is comprised of many different hardwood and softwood species. In general, hardwood mulches have a high carbon to nitrogen ratio. This means that in the process of decomposing they may temporarily reduce the supply of soil nitrogen fertilizer to mulched plants. Compared with other mulches, hardwood mulches tend to lose more of their decorative appearance over time, weathering to a gray or silvery gray color.

In municipal areas it never seems to amaze me as to why residents rake leaves to the curb to be picked up by the local governing authority. Trees take up minerals from the soil in production of leaves. When the leaves drop in autumn, they contain organic compounds taken from the soil. By mulching these leaves with a mulching mower, the organic material returns into the lawn. Likewise, leaves used as mulch around perennials also will return the organic compounds back to the soil the following summer.

Mulching perennials for the winter is a great way to help them survive the winter. Just like mulching your landscape plants during the summer, mulch provides organic matter to the soil. Mulch moderates soil temperatures, preserves soil moisture, suppresses weeds; and as the mulch slowly decays, it contributes to the organic content of the underlying soil.

Have fun mulching!