Mulch mad­ness

We go crazy for this ground cover, but many of us are mis­us­ing it.

The Washington Post - - LOCAL LIVING - adrian.higgins@wash­ @adri­an_hig­gins on Twit­ter Adrian Higgins GAR­DEN­ING

Au­tumn is knock­ing on the door, an op­ti­mal time for cer­tain an­nual tasks in the gar­den — re­seed­ing a thread­bare lawn, plant­ing trees and shrubs and di­vid­ing tired peren­ni­als.

But th­ese tasks seem to spur the most fas­tid­i­ous among us into fur­ther ac­tion by cut­ting back ev­ery wan­ing peren­nial and an­nual and then open­ing the flood­gates for a sea of mulch. This yard scrub­bing leaves the neat­nik poised and ready to in­ter­cept the very first leaf to yield to grav­ity.

Mulches come in many forms, but they all seem to share a power of mind con­trol over oth­er­wise sen­si­ble folk. Each year, we spend an es­ti­mated $1 bil­lion to cover soil with de­cay­ing or­ganic mat­ter, and I can’t help but think that much of it is un­nec­es­sary and even harm­ful to our plants.

For sure, mulch has its place. A thin layer, an inch or two, will go a long way to­ward pre­vent­ing weed ger­mi­na­tion, re­tain­ing mois­ture in the soil and sup­port­ing mod­er­ate soil tem­per­a­tures. As it de­cays, it adds ben­e­fi­cial hu­mus to the earth.

If I go to my rest hav­ing elim­i­nated the phe­nom­e­non known as the mulch vol­cano, I feel my life will have been worth it. I’m jok­ing, of course; no one will bring that prac­tice to an end.

The vol­cano is that mound of mulch piled at the base of a tree trunk. Widely em­braced by many land­scap­ers and home­own­ers who em­u­late them, the mulch vol­cano has no re­la­tion­ship to the needs of the tree. In­stead, mulch piled against the lower trunk pro­motes de­cay of the tree’s pro­tec­tive bark, har­bors gnaw­ing ro­dents and causes roots to grow detri­men­tally.

Where did the vol­cano come from? When a tree is newly planted, the root flare at the base of the trunk should be set an inch or two above grade, and the soil around it should be formed as a dish with a cir­cu­lar lip about three feet in di­am­e­ter. This traps wa­ter and feeds it to the tree’s newly planted root ball. You then place mulch over this saucer to re­tain mois­ture, but not with any mulch against the trunk. At some point, this mor­phed into a trunk scarf.

Casey Trees, the non­profit or­ga­ni­za­tion founded to help re­store and main­tain the Dis­trict’s ur­ban for­est, uses a mantra of “three-three-three,” said its ex­ec­u­tive di­rec­tor, Mark Bus­caino. That is, a mulch cir­cle that is three feet in di­am­e­ter, three inches thick and three inches away from the trunk. “For some rea­son, peo­ple think mulch vol­ca­noes are aes­thet­i­cally ap­peal­ing, so land­scape com­pa­nies aren’t will­ing to change their prac­tice,” Bus­caino said.

Af­ter a few years, tree roots ex­tend way past the tree’s canopy, so the only value in mulching around the trunk would be to keep away lawn mow­ers and string trim­mers. Yes, it’s hard be­ing a tree.

The other big but less ob­vi­ous mis­take with mulching is in lay­ing the stuff too thickly. When you do this, roots of trees and shrubs either be­come smoth­ered by the mulch and clamor for air and wa­ter or be­gin to grow into it. In ad­di­tion, re­searchers have dis­cov­ered that ex­ces­sive amounts of hard­wood mulch cause man­ganese and other el­e­ments to build up to lev­els that are toxic to plants.

Be­cause mulches fade in sun­light and as they de­cay, some peo­ple re­plen­ish mulch too of­ten, in­creas­ing the thick­ness of it and com­pound­ing the blan­ket ef­fect.

There is an art to lay­ing mulch, a skill that goes hand in glove with not ap­ply­ing it too thickly. In ad­di­tion to keep­ing it away from tree trunks, you should make sure mulch doesn’t build up at the base of shrubs, es­pe­cially such sur­face-rooted bushes as aza­leas and box­wood. Mulch piled against shrubs will cause them to grow roots into the mulch. When the mulch de­cays, the roots are left high and dry.

The top growth of peren­ni­als withers in the fall and win­ter, but the crown of the plant re­mains year-round at or just be­low soil level. This is where the buds for next year’s growth are gen­er­ated. If you smother a peren­nial in mulch, you up­set the plant’s bi­ol­ogy and run the very real risk of keep­ing the crown wet dur­ing win­ter dor­mancy, and it will rot.

I avoid or­ganic mulches on peren­ni­als that need free drainage and good air cir­cu­la­tion, such as bearded irises, laven­ders, rose­mary and sages.

In re­cent years, con­sumers have be­come mes­mer­ized by mulch that has been dyed. The most pop­u­lar col­ors are brown, red and black. What’s the al­lure? Ap­par­ently, some peo­ple don’t like the idea of their mulch grow­ing pale. Some brands guar­an­tee that their col­ors won’t fade for a year.

There is a prece­dent for this taste. At cer­tain pe­ri­ods in land­scape his­tory, gar­dens were dec­o­rated with col­ored glass, peb­bles and stone chips, to form em­broi­deries on the ground. I think of dyed mulch the same way, as a way of hav­ing un­chang­ing pat­terns and hues upon the land. It seems a per­fect so­lu­tion for those who want a gar­den but don’t want to fuss with plants.

Most gar­den­ers I know are un­com­fort­able with dyed mulch, and not just be­cause it sub­or­di­nates the role of plants. While tra­di­tional hard­wood, soft­wood and bark mulches are byprod­ucts of the tim­ber in­dus­try, some dyed mulches rely heav­ily on re­cy­cled wood as their source. The worry is that there may be preser­va­tives and other con­tam­i­nants in the mulch that you wouldn’t want in your gar­den.

Robert LaGasse, ex­ec­u­tive di­rec­tor of the trade group that cer­ti­fies mulch prod­ucts, the Mulch & Soil Coun­cil, said that “there’s noth­ing wrong with re­cy­cled ma­te­rial if you do it cor­rectly.” Bags of mulch that bear the coun­cil’s seal have been tested to en­sure that they don’t con­tain lead paint, chro­mated cop­per ar­se­n­ate and other con­tam­i­nants found in old build­ing ma­te­ri­als. Look for the coun­cil’s im­pri­matur.

I asked Roger Davis, a se­nior gar­dener at Long­wood Gar­dens in Ken­nett Square, Pa., what his ideal mulch would be. He of­fered two. He likes triple-shred­ded hard­wood bark, which is dark and fairly fine but doesn’t break down as quickly as sim­ple shred­ded hard­wood. He also likes leaf mold, which con­sists of tree leaves that are half­way to­ward be­com­ing dark, crumbly com­post. You can buy bagged leaf mold or, in many ju­ris­dic­tions, get it from your lo­cal govern­ment in the spring as the pre­vi­ous fall’s leaf col­lec­tion. Down­side: It may have some trash in it.

Bet­ter yet, you can make your own leaf mold. Gather the fallen leaves of au­tumn, shred them with your mower and either put them in a pile to com­post or in plas­tic bags to store. The re­sult­ing leaf mold can be used as a mulch next spring.

Al­ter­na­tively, just spread the chopped up leaves on your gar­den beds this fall. By minc­ing them, you get a neater look, and the shreds are less likely to blow around. Ev­ery­thing about this prac­tice seems right. The soil crea­tures con­vert the leaves into hu­mus, you’re keep­ing yard waste on site, and the price is right.


The cor­rect method, form­ing a rain-catch­ing dish over the roots but with no mulch against the bark.

We picked on a red­bud tree to show a mulch vol­cano, which if left in place will dam­age the base of the trunk.

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