Growing Concerns 462: Annual best, weedkiller drift, vole control, Hydrangeas

Dear Gardeners,

Here are more short reports on the hottest topics from the record-high stacks of letters and email we've received this spring.

Best annuals for sun
• When weedkiller drifts from the neighbor's, and other property line disputes
Voles controlled with traps and baits
Blue and pink hydrangeas won't bloom
• Thumbs up AND down advice for tree planting

The best annual sunny flowers

For the best floral display in full sun, don't look to the rare and unusual. Stick with tried and true plants that have been popular a long time. These reliable money-makers attract more research dollars, which means more varieties are bred, giving us more choices in colors, heights and disease-resistance varieties.

Our suggestions this year are salvia, petunia and marigold in beds that are well watered and fertilized. Sweet alyssum, globe amaranth (Gomphrena globosa ) and cosmos may fare better in average to dry beds that aren't so rich in nitrogen.

Lasting answers to border disputes

These involve diplomacy as well as horticultural craft. Take a property-line problem such as plants killed by a neighbor's drifting lawn herbicide. Short wooden fencing can block or absorb most of an over-spray, temporary plastic covers for at-risk plants can prevent problems, and immediate hosing-off can mitigate the effect. Yet all of these work even better if you involve the neighbor and/or the neighbor's lawn care firm.

When you take the problem to others, avoid emotion and accusation. Such events are more often accidents than deliberately destructive acts and misdiagnosis is always possible, so allow for both possibilities. "I think some lawn weed killer might have gotten onto these plants. It's possible they keeled over from heat stress but it looks more like the pesticide burn shown in the 'Ortho Home Problem Solver.'"

Use a problem-solving approach, in which you expect to give and well as get, "I'll install some edging and keep the seed heads cut off of the plants on that edge so they don't pop up as weeds in your lawn. So you shouldn't have to spray right at the edge. Could you pay special attention there to keep the spray from splashing or blowing?"

Vole control: Traps, poison baits

Looks like we'll have another year of vole trouble, what farmers called a "mouse year." If you note trails carved into lawn or beds -- shallow trenches the diameter of garden hose -- and clean holes into the ground the size of quarters or poker chips, voles are living there.

These rodents, also called meadow mice, are mouse-sized but active by day and prefer the outdoors where they eat the crowns and roots of lawn and other plants.

Don't ignore them -- in a mouse year a pair of voles in spring can become a clan of 100 by August. Natural predators such as hawks, owls, foxes, coyotes, cats and rat terriers can't keep up.

Place a mouse trap next to every hole. Bait it with peanut butter, smeared on both the top and underside of the trap's trigger. Make a cover for each trap -- notch the rim of a cardboard box to make a vole door, then invert the box over the vole hole and trap to darken the area. A brick on the box will hold it in place even on windy days.

Check and reset traps daily -- it's not unusual to catch dozens of voles in May of a mouse year.

Poison baits are another option but keep them under wraps to keep other animals from being killed. This includes anything that preys on mice and other rodents and might pounce upon a poisoned but not yet dead vole. It's been reported that some rodent populations are building resistance to the anti-coagulants in some products, so poison meant to kill can "walk around" in a resistant vole's body and end up being fed to a young owl, nestling hawk or fox kit. So do all you can to keep vole killing "under cover."

The best cover we've seen for such baits is a length of plastic plumbing pipe about 1-1/2" in diameter, cut in half with a "T" spliced in. Put bait into the pipe through the "T", then cap that opening. Leave the ends of the pipe open and lay it on the ground, "T" up, where voles are active.

Mice and voles can crawl in to the bait but rain, birds and pets are not so likely to reach it.

The pipe is also handy in tangled settings, such as a bed of thick groundcover Euonymus or Cotoneaster being ravaged by voles. You can slip the pipe under the plants' stems so it's on the ground and hidden, yet you will be able to refill the bait if you leave its "T" protruding.

Hydrangea questions never end!

If your blue or pink hydrangea has refused to bloom or bloomed only scantily, it will probably disappoint you again this year. It's not your fault, fertilizer makes no difference, and it's unlikely you can change the situation.

Winter cold kills the tip buds of Hydrangea macrophylla and H. serrata, the mophead and lacecap hydrangeas. Once those tip buds are killed, so is the plant's potential to bloom that year. You can tell in spring if you have a chance for flowers by checking the large bud at the tip of each branch. If it's plump and firm, like a good head of leaf lettuce, the winter was mild enough to spare it and you may get bloom. If it's dried out or blackened, don't bother hoping.

In a mild winter we've seen plants with live tip buds in early April... although we often see those survivors killed by spring frosts.


Green thumbs up... starting small rather than planting 10- and 20-foot trees. A larger tree loses more root in a move, up to 90% of its roots, so it requires far more care than the impatient gardener will give. A big transplant often dies back, succumbs to pests, or finds itself four years later looking up to a healthier, faster growing "small" tree planted at the same time.


Green thumbs down... mulch stacked against the trunk of a tree. No matter whether the tree is young or old, the heat and moisture quickly begin destroying the bark, the tree's foremost defense against insects such as borers and diseases like butt rot. That tree will eventually snap at the base. We may blame it on a storm or errant motorist, but it's the mulcher's fault.



First published 5/4/02, updated 4/11/14