Gardening Column

Voles continue to be a problem

Meadow mice, more properly known as voles, are short tailed and plump. They can’t climb much so spend their lives in shallow tunnels or foraging on the surface. Their populations rise and fall for reasons that are still obscure. Right now, numbers seem higher than average.

Voles cause a lot of damage in winter. When food gets scarce and especially when there is snow on the ground, they turn to young trees and shrubs for dinner. After snow melts, there are often 2-3 –inch vole holes in patches, evidence of a lot of activity in the area. Their gnawing can girdle trees at the soil line or remove roots. Next spring, your trees leaf out but without roots and the “plumbing” in the stem, can’t move water and they die. Voles also love carrots, beets, and potatoes left too long in the ground.

To reduce damage, you have to make voles uncomfortable. Cut grass short near trees so voles are more visible to the owls, cats, and hawks they fear. Trap moles since their tunnels provide safe access for voles to roots. Collapse the tunnels if possible. Finally, be careful in the use of mulches including landscape fabric and black plastic - they provide vole cover.

I have had several recent calls involving voles and mulch. One was a blueberry patch with grass clippings piled around the plants to conserve moisture. But covering soil in a 6-8 inch radius of the stems encouraged voles to gnaw without fear. A similar thing happened with a very heavy bark mulch application around young fruit trees. Most of the trees were a total loss. Finally, I once visited with a gardener that planted a new rose bed. He worked the soil, put in a drip irrigation system, and covered the bed with landscape fabric. Then he planted his new roses through holes in the fabric.

In the second year of growth, the gardener started to “high prune” his roses in November. As he pruned, he felt them to be poorly anchored. He tugged on one and it pulled right out. It had virtually no roots. It was much the same with the rest of the roses. The voles had been in food heaven, eating rose roots that they dearly love, protected by the fabric from any predators. The fabric was removed and all but a few of the 25 or so roses had to be replaced.

Trapping voles can work if pursued persistently. Standard mouse traps will work. Dig a shallow “swale” about six inches deep, about two feet wide and four feet long. Put some apples pieces in there and then cover it with a piece of plywood or some other cover that you can keep in place, leaving openings at both ends. If you see vole feeding on the apple pieces, place the traps in the swale, bait them with peanut butter, and cover the swale back up. Voles, unlike rats, aren’t very savvy and you can trap vole upon vole with the same traps in the same place.

There are a lot of issues with vole baits injuring non-target animals and there are few if any baits registered for home use much beyond the immediate area adjacent to structures. If you feel you can use them in your situation, please read and follow all instructions. The bait will need to be placed where nothing else but voles can get to it.

Encouraging barn owls

Barn owls were once considerably more common around Columbia County. The transition from the old-fashioned hip-roofed bard to the modern pole barn has removed some nesting sites. In addition, the conversion of farms to residential living has removed lots of farm structure period.

Yet, these birds are tremendously valuable. They will eat 5-10 rodents per day. Besides, how can you resist the chance to see their ghostly flight through a moonlit night? Or the opportunity to collect and take apart owl pellets to see the skulls of their prey within.

This link describes design and placement for barn owl boxes. They have researched the size that works best for them and other issues with having them adopted by the owls. The best time to install them is late fall through February. What a great weekend project. If the link below is too complicated for you to use, email me ( and I will send you a PDF of the article.

Spider symmetry

If you’ve ever looked at spider webs, you probably have noticed that some are rather straight forward affairs and others have a lot of extra zig-zaggy silk added to the structure.

It is the business of biologists to speculate on these subjects. Are the extra strands of silk there for reinforcement? The best evidence indicates that the “stabilimenta” is not rein-forcing material. So why do certain spiders expend the time and resources to produce it?

Because they catch more bugs. A scientist monitored the prey interception rates by noting the damaged areas in the web. He found that those decorated with the silk strands had 72% more “hits” from flying insects than those without the extra silk. His theory is that the extra strands reflect more ultraviolet light, making those webs more attractive to the flying insects that orient themselves to UV. These insects include many pollinating in-sects that use UV patterns from plants to guide them.

Have questions?

If you have questions on any of these topics or other home garden and/or farm questions, please contact Chip Bubl, Oregon State University Extension office in St. Helens at 503- 397-3462 or at

Free newsletter

The Oregon State University Extension office in Columbia County publishes a monthly newsletter on gardening and farming topics (called County Living) written/edited by yours truly. All you need to do is ask for it and it will be mailed or emailed to you. Call 503-397-3462 to be put on the list. Alternatively, you can find it on the web at and click on newsletters.

Many Extension publications available online

Are you putting up salsa, saving seeds, or thinking about planting grapes? OSU has a large number of its publications available for free download. Just go to Click on publications and start exploring.

The Extension Service offers its programs and materials equally to all people.

Contact information Oregon State University Extension Service–Columbia County


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