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What to do when voles destroy your garden

Also, what can you do about those raggedy lavender plants?|

Question: I have a small garden being invaded by voles. They are eating my plants and digging up the soil and mulch around them. What can I do?

Answer: Voles, moles and gophers all can cause problems and frustration in your garden. Since all three make tunnels, it’s important to identify the problem before you try to remedy it.

Moles (Scapanus spp.) eat worms, insects and other invertebrates and make round, volcanic-shaped mounds. Pocket gophers (Thomomas spp.) eat bulbs, roots and whole plants from underground tunnels and form crescent-shaped mounds with plugged holes. And voles (Microtus spp.) eat plant material and travel along above-ground runways connecting multiple burrow openings about 1.5 to 2 inches wide.

With voles, you may need to pull back the overhanging ground cover to find these runways, which contain clippings of fresh grass and tiny, greenish-color droppings.

Voles are quite destructive, consuming grasses, herbaceous plants, bulbs and tubers. They also will eat the bark and roots of woody plants.

Vole numbers fluctuate from year to year, and favorable conditions can dramatically increase their numbers. The best way to prevent vole damage is to manage the population before it expands to damaging levels. Here are some ideas for controlling vole populations:

  • Make conditions in your garden unsuitable for voles. Weeds, heavy mulch and dense vegetation provide food and cover. Limit these conditions through regular weeding and mowing. If you have space, maintain cover-free areas to discourage vole movement into garden beds. Maintain open, 4-foot-diameter buffers around woody plants.
  • Exclude voles with wire fencing that has a mesh size of ¼ inch or smaller. Fencing should reach at least 12 inches above ground and be buried 6 - 10 inches below ground. Fencing can stand alone or be attached to the bottom of an existing fence.
  • In small gardens, try trapping. Place traps along vole runways at frequent intervals and continue to trap in the same areas until you stop catching voles. Depending on garden size, you may then need to move to another location 15 - 20 feet away.

Many methods suggested for vole control either don’t work or don’t work very well. Commercial repellents are best applied before damage occurs, and it’s impractical to apply these products underground where damage may be occurring. Fumigants are ineffective in shallow vole burrow systems. And while many animals and birds eat voles, they generally do not significantly limit vole numbers.

It is difficult to control large populations of voles, particularly if you have a booming population or a large infested area. In these instances, your best bet is to call a commercial pest control expert.

Identify mole, vole and gopher damage: bit.ly/3B5BKSQ

Control voles: ipm.ucanr.edu/PDF/PESTNOTES/pnvoles.pdf

Question: I planted several lavender plants this year, but with the end of summer, they’re looking raggedy. What should I do to get them ready for winter?

Answer: This is a great question, since lavender (Lavandula ssp.) is a favorite in so many Sonoma County gardens. Lavender is treasured for fragrant blossoms that can be added to food and herbal concoctions; it also attracts bees and repels deer.

Native to the Mediterranean areas of Europe, lavender is acclimated to warm, dry summers and cool, wet winters, just like we have in California. It thrives when planted in full sun and in well-drained, gravelly soils. If you have heavy clay soil, plant lavender on a mound, so the excess water drains away from the root crown. Water the roots of young plants when the flowers are developing, preferably with drip irrigation kept well away from the main stem. Once established, lavender needs little water. Avoid overhead watering; it promotes disease and can break lavender plants.

Ideally, pinch back lavender when it is planted, to encourage a low, woody, branching shape as it matures. If you leave young lavender alone, only a single stem develops, and the plant eventually becomes top-heavy. In wet and windy conditions, it simply splits apart.

Prune lavender after it blooms and use the cut flowers in bouquets. If it blooms early in the summer, pruning may encourage a second bloom cycle. When shrubs are pruned only in the spring, the first flowering is delayed and a second bloom may not occur. Even if it doesn’t bloom a second time, lavender needs to be cut back severely in the fall, to maintain shape, prevent breakage and encourage spring blooms.

Look at the lower woody stems to find the bluish-green points that indicate emerging buds. For severe pruning, cut just above the third bud from the bottom of the stem. This cut removes all leafy growth and forces out new side shoots from the remaining buds. If you make cuts any lower, into the woody stems, you can kill the plant.

If you have a lavender plant that is more than three years old and has never been pruned, it may become woody with gnarled branches. If protected from wind, it may live for 10 - 20 years, but more likely it will be short-lived. You can try to regenerate a woody plant by pruning the remaining green down to just above the wood and hope for new growth. Dry wood on lavender usually does not re-sprout.

Local nurseries offer a wide variety of lavenders, from fast-growing, sturdy English cultivars such as ‘Grosso’ and ‘Provence’ that may reach 3 feet tall and wide to smaller ‘Hidcote’ and ‘Royal Velvet’ hybrids that hold their color well when dried. Spanish lavender (L. stoechas) and its cultivars re-bloom readily; it can be pruned to half its size in fall or after its second flowering. French lavender (L. dentata) needs little pruning, except to maintain its shape.

To ensure you plant a cultivar that will grow within the boundaries you prefer and lessen the need for drastic cutting back, look at the plant label for its mature size before purchasing.

For more information on lavenders, see:

“Lavenders for California Gardens”: bit.ly/3A7wflX

Types of lavender: bit.ly/2XCtpIw

Spanish lavenders: bit.ly/3A2RF3K

Lavender pests and disorders: bit.ly/3FaQfYH

Bees and lavender: bit.ly/3D6iO7D

Contributors to this week’s column were Janet Bair, Pat Decker, Karen Felker and Patricia Rosales. Send your gardening questions to scmgpd@gmail.com. The UC Master Gardener Program of Sonoma County (sonomamg.ucanr.edu) provides environmentally sustainable, science-based horticultural information to Sonoma County home gardeners. The Master Gardeners will answer in the newspaper only questions selected for this column. Other questions may be directed to their Information Desk: 707-565-2608 or mgsonoma@ ucanr.edu.

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