by Lee Squires
This is a major plant pest story. I used to overwinter my bonsai trees on the ground under 10-12” of cypress mulch, with plywood boards around the perimeter of the bed to block wind and keep out rabbits. I never had a vole problem.
Three years ago, I put up two hoop-style cold frames with white plastic covers for winter protection.
I also mulched the trees and covered the cold frames when the temperatures got consistently in the 30’s.
I laid down the black landscape fabric in the frames to hold down weeds and mud.
My trees were happy and healthy for two years, then ... 2012 was the year for invasion!
In February, when our temperatures started to warm, I opened the front flap of the frames to let out some heat. (And check for plant pest.) I noticed some minor bark damage on my ginkgos. It wasn’t too bad, but I was a bit annoyed by what I saw.
I closed the flaps when the temperature dropped, and opened them again in a couple of weeks.
Then, I began to see more damage.
All of my ginkgo trunks were girdled from the pot up 10-12” into the tree. All of the bark was eaten!
I noticed that the trees in my ginkgo forest were also leaning. I pulled on one and it came out of the pot. All roots were eaten down to nubs.
It was ruined. Three other ginkgo trees had the same fate. I noticed some minor trunk damage on my Japanese Maples.
Then I saw my Trident Maple. It was girdled from top to bottom with only a few limbs in the top left unscathed.
(Ironically, as of March 25th, it had totally leafed out. It had no root damage so it may be OK. Evidently, the cambium layer is still intact or some reserves are still active in the tree’s system.)
I then, frantically, pulled the mulch back from my Kiyohime Maples. Most all were girdled up 4-5”. When I touched the trees, they almost fell over. Only one or two roots were left holding the trees in the pots.
The voles had tunneled into the pots and start eating the roots from the bottom up until they ate most or all of them.
I looked at my evergreens and saw no trunk damage so I thought, maybe the voles don’t like pine sap and they mainly eat deciduous trees. I was wrong.
It turned cold again, and I had no choice but to leave my bonsai trees in the frames without creating a whole new over wintering area.
I set some mouse traps with peanut butter and apple pieces, hoping to catch this plant pest beast. Voles love apples.
The first day, one trap was missing so I figured a vole was wearing a trap as a sombrero in his tunnel.
In March, I opened the frames completely and removed the plastic.
I began checking all my bonsai trees for this plant pest damage and pulled back the mulch to expose the trunks and pots. Many of my pines had surface root damage but minor trunk damage.
I noticed a 25 year old Gnome Mugho Pine move in its pot. I pulled on the 2 1/2” trunk and the 20” tree easily came out of the pot.
All the mugho roots were eaten. Totally destroyed!
A Cork Bark Elm met a similar fate. The 15” tree had no trunk damage but the 1 1/2” trunk was severed at the pot line, like Bucky the Beaver had paid a visit.
Too ridiculous for words, however, I did manage a few commonly used expletives to describe what I saw.
All totaled, 12 of my trees were affected one way or another.
I had created an ideal environment for them. Thick mulch, a warm house free of rain and snow in which to live, with plenty of food and no reason to leave!
Also, I discovered on the internet, this plant pest loves landscape fabric. They tunnel under it and it provides shelter and warmth.
My mistake was using the fabric in my cold frames. Don’t use it in your landscape beds either.
After moving the mulch to some of my plant beds, as I always do, Pearl, our French Bulldog, sniffed out the nests. She found two nests and they were made of chewed up landscape fabric and mulch.
I like to use the covered cold frames for protection, so I will continue. However, next year I will not be using any mulch.
Hopefully, the roots will stay warm enough in the frames without mulch.
Also, I’m removing all landscape fabric today!
I will set mouse traps in the frames - baited with apple and peanut butter - before I close them up. I will set out several rodent bait stations in the frames too.
You can also place a trap at a right angle in the runway. They will automatically run over it and get caught but that is a problem if you have animals or children in the yard.
I saw a cool method of catching this plant pest on the internet that is pet and kid safe. Find their hole and place a mouse trap, un-baited, on two sides with the triggers facing the hole.
Cover the hole with a piece of gutter with one side cut out staked down with metal stakes; it will sit over the traps with a roof and two sides and act as a covered, dark tunnel for the vole. They will feel safe and come out of the hole and walk into the trap – since they can only move in two directions.
I plan to try the gutter method.
The damage and loss of some valuable bonsai trees from this plant pest is disheartening, to say the least.
However, Spring is the season for rejuvenation and birth. I plan on rejuvenating the ones that I can, birthing some new bonsai trees and eliminating my current vole population.
Taking care of bonsai trees is about more than watering and pruning, many thanks to Lee for sharing this 'bonsai trees and voles' story. The vole is a plant pest that may not be common, but when it arrives, it creates havoc!
Visit more Plant Pests and Bonsai
is my free monthly newsletter. Subscribe to get current tips, ideas and photos that may not appear on this site.