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

Carpenter Ants and Termites in Mulch

a closeup of pine bark nuggets in a white bag

Hello fellow readers, Today’s topic hits close to home. Sandy from Sparta, NJ, wrote, “Brian bought pine bark nuggets to mulch the garden, and there’s tons of huge black ants and some termites in it. What do I do?”

The close-to-home part is I’m tackling carpenter ants that nested in the screened porch as we speak. So Sandy’s dilemma is my dilemma too.

an open bag of Twin Oaks Pine Bark NuggetsI wrote back, “Oh my, Sandy!  If you already spread the mulch, then sprinkling it with diatomaceous earth should work well to kill both critters. But I’ll learn more about what to do about carpenter ants and termites in mulch— I feel a column coming on :^).”

Natural Remedies for Carpenter Ants and Termites in Mulch 

Diatomaceous Earth (DE) is fossilized remains of microscopic oceanic plants that destroy the waxy exoskeletons of bugs such as ants, termites, bed bugs, or fleas. Yet, it’s safe for people and pets. It’s used in grain-based foods to keep bugs from eating them.

I learned that oils such as clove bud and garlic oils are effective against termites, per the Journal of Agricultural and Food Chemistry. In addition, the U.S. Forest Service finds tea tree oil highly effective. You can apply the oil at full strength on the wood. Or, mix four drops per gallon of water and spray it, increasing the amount of oil if needed.

Then there’s readily available cedarwood oil. The only thing is cedar oil will burn foliage—so be sure only to spray it on the mulch. By the way, I recently learned cedar oil used as a spray kills ticks on contact; it’s what professional tick prevention services use to treat lawns.

My go-to neem oil is another remedy that Sandy could use on her mulch. Mix half a teaspoon of liquid soap first in four cups of water, then mix in one teaspoon of neem oil. The mixture breaks down in eight hours, so use it right away.

pile of saw dust looking carpenter ant frass in the corner

Evidence of Carpenter Ants on the screened porch.

Evidence of Carpenter Ants versus Termites?

It was a pile of sawdust that caught our attention in the corner behind a potted plant that clued us into our dilemma. Termites make small holes in wood and toss their frass out (their excrements) that look much like sawdust. The same is true of carpenter ants. So on with the investigator hat to learn which invader we have.

Carpenter ant frass contains ant parts they toss in mounds near the holes. There are no insect parts in termite frass that are uniformly rounded and often scattered rather than mounded around their entry points.

Remedies for Carpenter Ants and Termites Inside your Home 

You can DIY by mixing one part of natural dish soap with two parts of water and apply using a sprayer. So I came up with the idea of boiling up pots of water, a remedy dear old mom used to kill ants, and mixed the prescribed dish detergent. But when I vacuumed up the frass to find the entry holes, they were on the side of the wood molding. Too high to get the boiled water into them. Dang.

small holes in wood molding caused by carpenter ants

The entry holes are too high to get the boiled water into them. Dang.

A half-cup of white vinegar mixed with a half cup of lemon juice can also work, but it changes soil acidity, negatively affecting plants. Likely a good idea for my dilemma on the porch to spray into the holes, though. Or is there a way to somehow siphon it in with a small hose to kill the trespassers? But, hey, I’m growing desperate.

They suggest repeating the process a few times, then see if it’s effective. FYI— if there’s a reappearance of frass, it didn’t work, then it’s likely best to call an exterminator.

It made me think of Groundhog Day
a single black carpenter ant on beige tile

For several days, one stray carpenter ant visited my writing spot

There’s a funny (or maybe not so funny) preamble to the story before finding our intruders. First, I noticed a single black ant, a sizeable one, climbing the wall in front of my writing spot. Then, each morning about the same time, one came trailing by in the same place.

It made me think of Groundhog Day; every day, the same event unfolded at the same time. I knew it wasn’t the same ant, though. Let’s just say, unlike most insects that I release back to the wild, I have no mercy for ants.

It turns out the single ants were worker carpenter ants looking for other places to nest. Then they leave pheromone signals to call in their buddies. Ugh! It’s interesting how we have selective compassion for uninvited guests. Garden Dilemmas? (and your favorite Podcast App.)

Ants around your patio? Link to a previous column titled Ants be Gone

Link to the abstract in the Journal of Agricultural and Food Chemistry about clove bud and garlic oils.







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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