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Ask the Gardener: Have hemlocks had their day in the Northeast?

Award-winning writer Carol Stocker also talks about tomato plant and spring bulb care. Get more expert advice at

Woolly Adelgid is not the only thing threatening hemlock in the Northeast. Dina Rudick/Globe staff/File 2007

What to do this week Move potted houseplants outside to a partly shady spot out of the wind for their summer vacations and group them for easier watering. Be sure to add drainage holes or gravel to the bottom of the containers so the roots don’t drown. Give new plantings, including trees and shrubs, an inch of water weekly, preferably in the early morning. Growing tomatoes in cages is a good compromise between staking and sprawling. Snip small suckers from between the branches of tomato plants and remove foliage shading ripening fruit. Apply water-soluble organic fertilizer monthly. Be sure to pull invasive plants such as garlic mustard before they go to seed. Watering an area beforehand makes weeding easier. If you have trouble telling weeds from flowers, remember most weeds are shallow-rooted annuals that respond to a gentle tug. Maintaining lawns at 3 inches retains more soil moisture and helps shade out weeds. Summer mowing should be weekly or even less often.


Q. My husband and I have tried various remedies on our row of hemlock trees to eradicate the woolly adelgid to no real benefit. Do you have a tried-and-true application to suggest?

S.H., Hingham

A. The threat from this tiny-but-deadly aphid relative from Asia, named for its tiny gray, woolly balls of fluff that line the underside of hemlock branches, is increasing with our milder winters. Infected hemlocks can die in less than five years unless treated. Frankly, if you have a hemlock hedge, it makes sense to replace it with either a fence or a row of evergreen Arborvitae plicata, such as the Green Giant variety, which grows tall, narrow, and fast and is so bulletproof that deer won’t eat it. I would not plant more hemlocks because of their pest problems, which now include elongate hemlock scale, which is almost as deadly and common as woolly adelgid, according to George Barth, plant health care manager at Hartney Greymont tree care services of Needham and Concord. “It produces orange-brown waxy spots that you can see through a magnifying glass on the underside of the needles.’’ Talk about a one-two punch!

Barth adds that “hemlocks hate hot weather,’’ so climate change is coming to get them, too. If you want to prolong the life of some beloved specimen trees, as I do, start by calling in a certified arborist for a diagnosis, treatment proposal, and price estimate. Ask whether the trees are too far gone to merit ongoing treatment, which could easily run hundreds of dollars per tree per year for multiple problems.


If your hemlocks have only woolly adelgid, you could try treating them with an over-the-counter formulation of imidacloprid, said Todd Caswell, arborist and manager at Natural Tree & Lawn Care of Avon. But I tried this and it didn’t work (the dosages are tricky), so I hired their licensed pesticide applicator to drench the soil around my large hemlock with imidacloprid every other year for about $200 for one tree. I also give my hemlock a lot of extra water in the summer. It is worth it to me because it is a stately native evergreen that provides year-round privacy, plus a 70-foot-tall nesting site for chipping sparrows, robins, and even a red squirrel. But it is definitely on life support.

Q. If I got tulips and hyacinth to bloom indoors, how do I preserve the plants for next year? And why are the leaves turning yellow on my allium?

G.F., Millis

A. Some hardy spring bulbs such as hyacinths that are “forced’’ to bloom indoors, will bloom again in future years if you plant them outdoors, but this doesn’t work with tulips. All bulbs like allium must photosynthesize to store energy if they are to rebloom next year, so don’t remove their leaves until they turn completely yellow.

A new garden to visit

The Trustees of the Reservation’s Long Hill property in Beverly unveiled a plant-rich and innovative perennial garden by Julie Moir Messervy Design Studio on June 26. It overlooks one of four recently reclaimed hilltop vistas. It is all part of the ongoing transformation of Long Hill into a world-class public garden. As part of the Trustee’s horticultural transformation, new garden spaces also have been created at the Stevens-Coolidge House & Gardens property in North Andover. Planning was done in conjunction with Mikyoung Kim Design and Maryann Thompson Architects.


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