Oh-No, Volcano

There’s an eruption occurring in some yards in Clay County. You might see it in a neighbor’s yard, along a lovely planted streetscape or in a parking lot you frequent.

As spring landscapes are refreshed, in some landscapes little volcanoes are cropping up like island chains, surging around the bases of trees and shrubs. Have you seen this phenomenon? Perhaps you’ve even copied the volcano look, thinking that if so many people are doing it, it’s a proper technique. If so,-quick, grab your rake and turn your volcanoes into flat desert isles, then rush back and read more to see why this practice should be discouraged in any landscape.

It’s a common mistake that gardeners-and even seasoned professionals-make. By correcting it quickly, your landscape plants will thank you.

Volcano mulching, or the practice of piling much deeply against the trunk or stem, will ultimately hurt the health of any plant and may even be its death sentence. For shrubs and trees that have just been plant- ed, the volcano encourages improper root development.

Soil at the surface level will become waterlogged under the volcano, creating the perfect conditions for rotting and suffocated roots. The roots will try to grow up through the mulch rather than out into the surrounding soil. Eventually the roots that develop in the volcano will dry out the mound of mulch as they seek moisture, inducing drought conditions that further stress the plant.

With certain mulches, the umbrellashaped top surface can experience fungal activity that makes the surface resistant to water saturation. Water will then shed off the volcano surface to the surrounding soil, and worsen the drought conditions within the volcano. This is especially true for mulches that naturally have a high carbon content, such as chipped or ground wood and sawdust. Too much volcano mulch-induced drying out and the plant will eventually die without ever properly establishing its roots in the ground.

Established plants are at equal risk from volcano mulching practices, though the effects are different. The risk of root rots is much higher, as roots already established in the soil are smothered and fail to adequately get necessary oxygen. At the trunk base, the excess moisture also results in rot and decay, weakening the supporting structure of the plant. More damage to the trunk can occur from rodents that may take advantage of the opportunity to hide in the volcano and gnaw on bark.

This type of damage opens the plant up to more potential fungal and rot problems. Volcanoes may also hide damage from girdling roots-those that circle the base and strangle the main trunk as they grow and expand. Just like a boa constrictor, a girdling or circling root may eventually cut off the circulation-in this case, of water and nutrients the plant needs to move up from the roots.

If you discover girdling roots when correcting a mulch volcano, you can carefully cut them to free the trunk as long as the root isn’t more than a third of the trunk diameter in size. Young trees respond well to this treatment. A trained arborist should be consulted for advice if the girdling root is large or if it’s become embedded in the trunk.

Mulch is generally a great thing for plants. Properly placed, mulch is fantastic at keeping in moisture and distributing it more evenly to roots. It helps moderate soil temperature, protecting roots from cold and heat extremes. It can keep weeds at bay, and even help block some soilborne diseases.

Mulch makes soil magic as it breaks down, enriching fertility and improving soil structure with better drainage and aeration. All of this greatly benefits your plants-but only an evenly distributed layer about two-inch to three-inches thick is helpful. Also, while mulch should be extended as far out as the drip line (or reach of the outermost leaves) whenever possible, it should never be placed right against the trunk or main stems of any plant. Leave a few inches clear against the trunk or stem of shrubs and up to 18 inches clear with large trees. Aim for at least an eight-foot diameter circle on large trees where it’s not practical to mulch the entire drip line, or consolidate multiple trees into a flowing ‘island’ bed of mulch. Proper mulching will save your plants as well as saving you money on mulch. Above all, avoid the volcano-too much mulch will smother your plants in the long run.

Want someone to answer a specific plant question for you?Go online to http://clay.ifas.ufl.edu and under the heading "Horticulture" (left hand side of page) left click on "Ask a Master Gardener" and a reply will be sent plus a hyperlink to the appropriate University of Florida Fact Sheets. Please send us a digital picture of the problem. To read past articles that might help you with seasonal problems and to learn about upcoming Extension Programming in our area go to our website at UF/IFAS Clay County Extension.

Seasonal concerns from gardeners

AMY E. MORIE

Environmental Horticulture Agent ll Clay County Extension Office