From the Director's Desk - Mulch: The Good, the Bad, and the Ugly

Plant health care does not begin and end with choos­ing the cor­rect plant for a site. Sev­er­al oth­er fac­tors can ben­e­fit or harm trees and oth­er plants, fac­tors includ­ing nutri­ent and water avail­abil­i­ty, soil pH, and prop­er prun­ing and mulching tech­niques.

​“Mulch” refers to mate­r­i­al placed over the soil’s sur­face to main­tain mois­ture and con­trol tem­per­a­ture. Over the long term, mulching also improves soil con­di­tions. It is impor­tant, how­ev­er, to use the prop­er mulching mate­r­i­al and apply mulch cor­rect­ly to gar­ner the ben­e­fits. Oth­er­wise, mulch may have lit­tle or even a neg­a­tive effect.

Organ­ic mulches are com­mon­ly used for mulching a land­scape or gar­den. These mate­ri­als will even­tu­al­ly break down and pro­vide nutri­ents, add organ­ic mat­ter, and improve soil struc­ture. Exam­ples of organ­ic mulch include wood chips, shred­ded bark, pine nee­dles, leaves, cocoa hulls, and com­post mix­es. Depend­ing on cli­mate and microor­gan­isms present in the soil, organ­ic mulches decom­pose at dif­fer­ent rates. The decom­po­si­tion process improves soil qual­i­ty and fertility.

Organ­ic mulches reduce the loss of soil mois­ture through evap­o­ra­tion and insu­late plant roots dur­ing times of tem­per­a­ture fluc­tu­a­tion. Mulching helps to sup­press weed growth and stop the ger­mi­na­tion of wind­blown weed seeds. It inhibits cer­tain plant dis­eases. Aes­thet­i­cal­ly, mulch pro­vides a uni­form look for gar­den beds and helps pre­vent dam­age from weed whack­ers and lawn mowers.

Though ben­e­fi­cial, mulch must be applied prop­er­ly to offer its full spec­trum of ben­e­fits to plants. Too much can actu­al­ly be harm­ful. The cor­rect amount of mulch applied should be between 2 ‑4” deep but not touch the base of a tree trunk or a plant stem. Deep mulch is often applied as a means to con­trol weeds and reduce main­te­nance, but it might actu­al­ly cre­ate addi­tion­al prob­lems such as root rot, nutri­ent defi­cien­cies, and tox­i­c­i­ty. Deep mulch can also cre­ate a habi­tat for rodents that chew bark and even­tu­al­ly gir­dle trees.

So how do you apply mulch cor­rect­ly in your land­scape or gar­den? To begin, con­sid­er fac­tors such as drainage. If drainage is poor, apply­ing a thin lay­er of wood chip mulch can help absorb excess water, improv­ing soil aer­a­tion as it breaks down. If drainage is ade­quate, apply a 2−4” lay­er of mulch out as far as the tree’s drip line or beyond if pos­si­ble. Make sure the mulch is not touch­ing the tree trunk but instead is at least 2” from it. Reap­ply mulch as often as need­ed, usu­al­ly once a year.

Mulching can be a plant’s best friend when applied cor­rect­ly — or its worst ene­my when not. Fol­low­ing these guide­lines will ensure health­i­er plants and few­er prob­lems for your grow­ing investment.