Garden Dilemmas, Delights & Discoveries, Ask Mary Stone, New Jersey Garden blog

Woolly Adelgid- Hemlock Mulch

Hello Fellow Readers,

At last, it’s the official start of spring! One of the chores many delve into, along with their spring cleanup, is freshening up their mulch. John from Andover asked what mulch he should use. Last week we spoke about the trend in using cocoa mulch but learned it could be toxic to pets. I’ve heard the sweet smell can attract wild animals, so best to stay clear.   We’ve spoken before about controversial dyed mulch made from recycled wood products such as wood pallets, old decks, and other construction debris often contaminated with harmful chemicals. Never mind the dye itself covering up the mystery of the wood products used – another stay-away if you wish for long-term healthy plants.

Hemlock Mulch

Hemlock Mulch

Cedar and hemlock mulch is said to have fewer mold spores than other hardwood mulches and doesn’t break down as quickly.  During my recent lecture at the Springfest Garden Show, A question was whether there is a risk of spreading hemlock woolly adelgid (HWA) by using hemlock mulch. Woolly adelgids are tiny insects that feed on sap on the twigs at the base of hemlock needles. It looks like white powder on the foliage.  It has devastated native stands and residential hemlocks, but the problem has dramatically improved, and hemlocks are once again readily used in the landscape.

In cooperation with the USDA, the UMass Center for Agriculture states, “given that hemlock bark mulch is made from the bark of the trunk and major branches; there should be limited or no adelgids present in those areas.” Besides, bark mulch should not be used as soon as it is made for other reasons than woolly adelgid. “If six months have passed from the time of manufacture, then the minimal movement of the adelgid would be expected onto another host.”

Bottom line, hemlock or cedar mulch is safe to use and a preferred choice compared to tomato sauce, red or other flavors of mulch. Garden dilemmas?

On a personal note:

I am grateful to The Press for their coverage of the Springfest Garden Show, but the acknowledgment for the Display Garden goes to my colleague and friend Marty Carson of Three Seasons.  Marty and I are associates and combine efforts on landscape & garden designs and lectures, but the Display Garden kudos goes to Three Seasons; I merely helped out.  Also, Three Seasons donates their talents and resources to assure the show is a great success making all of the common areas of the show fabulous. It’s a gift to our community. As you may know, the Springfest Garden Show is a nonprofit organization whose mission is to support education and facilities related to horticulture in our community.  Thanks to all that supported our event!


Three Seasons Springfest Garden 2014


Mary Stone, owner of Stone Associates Landscape Design & Consulting. As a Landscape Designer, I am grateful for the joy of helping others beautify their surroundings which often leads to sharing encouragement and life experiences. These relationships inspired my weekly column published in THE PRESS, 'Garden Dilemmas? Ask Mary', began in 2012. I dream of growing the evolving community of readers into an interactive forum to share encouragement and support in Garden and Personal Recoveries - seeking nature’s inspirations, stimulating growth, weeding undesirables, embracing the unexpected. Thank you for visiting! Mary

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