WICHE: Match mulching material with plant’s needs

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You have to choose the right substance for the right plant.

By Jeneen Wiche

Mulch has become a landscape staple, almost to a fault when it is over applied, smothering roots and girdling trunks.

When done properly mulch can help to suppress weeds, retain moisture and moderate temperature. These things can be achieved using a variety of materials, but which type of mulch suits your needs best?

Predominately we use organic materials for mulching. Organic mulches include plant- or animal-derived materials such as wood chips, pine needles, tree bark, grass clippings, composted manure and worm castings. Organic materials have the benefit of looking natural while adding varying amounts of nutrients to the soil.

I personally prefer a mulching material that is nutrient rich, so it improves the soil and provides food for the plant while serving its other practical applications.

Inorganic mulching materials include stones, gravel, landscape fabrics, plastics and even recycled tires. These may last longer, but they do not always provide the look that a homeowner wants for their landscape.

Because they take less maintenance, they are more often seen in high traffic or municipal areas then around our homes. Most things serve a purpose if used properly, but there are some concerns with certain inorganic mulching materials and their ability to allow a seasonal warm up and cool down of a plant’s root system.

 When we mulch to moderate soil temperature, we are usually mindful of keeping the roots cool in the summer. In the winter months, however, I think there is a mixed message about what mulch will achieve. Organic mulches used properly – 2 to 2.5 inches deep – typically allow for the proper warming and cooling of the soil as winter turns to spring and fall turns to winter.

Inorganic mulches, however, may cause some delay in the process resulting in winter damage.

In the article “Using Mulches in Managed Landscapes” (a cooperative effort by Iowa State University, Ohio State University and University of Kentucky), the authors state, “Mulch effects on root-zone temperature, as well as any potential benefits or consequences for plants, will vary considerably depending on factors such as properties of mulch, soil type, soil moisture, plant species or cultivar, and weather patterns.”

I bet you never realized that the type of mulch you choose could have such an effect on the plant you are trying to care for.

I mention all this because we need to understand that mulch can create an environment that may make it difficult for the plant to acclimate accordingly from season to season.

Too much mulch before the ground freezes is like having a bikini on underneath your full-length fur. Take the coat off, and you’re in for a shock once winter hits.

A plant’s root system needs to cool down and slowdown in order to go dormant sufficiently before you mulch the area to prevent heaving and thawing. Always wait for several hard freezes before you apply mulch for moderating winter soil temperatures.

The same thing can happen in the summer if certain types of materials are used as mulch. Wait until the soil has a chance to warm up a bit before you apply mulch, otherwise you may insulate the cool soil and delay the warm up, thus delaying plant growth.

The use of s various inorganic mulches really can fool plants, too. Using black plastic, for instance, is like keeping the fur coat on all summer, not to mention that it doesn’t allow for healthy amounts of oxygen to reach the root system. This can cause double trouble once winter rolls around again, too. The plant will be slow to go dormant because the root system is still warm and therefore it will be more susceptible to winter damage.

Even using crushed brick, rock or pea gravel may speed up the warming process in the spring. The university extension article on mulches cited an example in which a red maple broke dormancy early in the spring (around here that means it would likely suffer from late frost damage) likely due to the brick and pea gravel’s capacity to conduct heat to the underlying soil. Gradual warming and cooling of the soil is best, and mulch should be used to moderate the soil temperature seasonally.

None of this is to say that you should not use certain materials as mulch, however match them up accordingly with what you want to achieve and what the cultural realities are for your plants.

Use black plastic around your tomato plants. These annuals love warm soil, and they only live a short time.

I would avoid using it with anything that lives longer than a couple of months, though.


Check out gardening columnist Jeneen Wiche’s work at www.SwallowRailFarm.com. You can find her columns also at www.SentinelNews.com/agriculture. She answers questions once a month in SentinelNewsPlus. To submit a question, send an E-mail to jwiche@shelbybb.netand type “Sentinel-News” in the subject field.