Ask the Gardener: This pretty plant invader will disrupt your Zen

Award-winning garden writer Carol Stocker takes readers questions about garlic mustard and Eastern redbuds.

Garlic mustard, coming to a garden near you. Globe File 2017

May 5, 2021

What to do this week Get outdoors and enjoy the beauty of spring, which is early this year. You can start sowing or transplanting warm-weather vegetables such as corn, tomatoes, peppers, bush and pole beans, melons, cucumbers, and squash outdoors now in Southern New England, but plant them again in two weeks as a backup and to stagger your harvest so all your crops don’t all come at once. Push your planting date back two weeks in colder parts of New England. Wait two weeks to plant tender flowers and vegetables, because we could still get a late frost. Keep new lawns and other plantings watered if the weather is dry. Set your mower at 2½ inches to encourage tall grass to shade out weeds and develop deeper drought-resistant roots. Keep pruning, weeding, and fertilizing. Most large tulips won’t bloom again ever, so I treat them as expensive annuals and just discard the leaves, stems, and bulbs after blooming to devote their space to vegetables or annuals for the summer. Cut brown, dead branches on roses and other shrubs back to just above the nearest live green bud or branch.

Q. Is this garlic mustard? We’ve been enjoying this lovely plant. It is currently the queen of our garden. Would hate to rip it out.

C.S., Concord

A. When people ask me about a mysterious new plant that has appeared unbidden in their yard, it is almost always an invasive — and the vanguard of thousands more if it is allowed to stay and multiply. Such plants are often pretty, and the homeowners are often hopeful that something desirable and free has come to visit. Alas! It doesn’t work that way. The photo you sent me shows a dastardly garlic mustard plant in full bloom in your perennial bed, its clusters of four-petaled white flowers facing upward at the very top of a straight vertical stem about a foot tall that is lined with pointed and jagged leaves. It is sitting there poised to take over the rest of your flower bed. Like most invasives, it has a couple of tricks up its sleeve. It will produce up to 1,500 seeds per plant with a 100 percent germination rate. It also produces chemicals to suppress the growth of everything else around it. Soon you will have a solid field of garlic mustard where once there was a mixed community of plants. The last trick is that seeds from a single plant will patiently take turns sprouting for five years afterward. As the old saying goes, “One year’s seeding, five year’s weeding.’’ So pull it and bag it. And keep an eye out next May for new ones. The good news is that garlic mustard is one invasive weed that is easy to pull.

Q. I have an Eastern redbud that I planted about five years ago that appears to be diseased. Can I save the tree, or am I better off just removing it to save my other redbud?

G.T., Littleton

A. Redbuds are native understory trees that tolerate dappled shade but need extra moisture or mulching. Like native dogwoods, they bloom now before leaves appear. Small pea-like flowers line branches with fuchsia tracery. From the photo you e-mailed, it looks like yours has burls caused by insects laying their eggs in the trunk or bark. Don’t give up yet, as many trees can coexist with this and I doubt it’s a threat to other redbuds. Give it extra water through droughts, however, as redbuds are less vigorous than many tree species. Some landscape designers jokingly call them “deadbuds’’ because they don’t survive challenging conditions. I have planted three myself. One became a “deadbud.’’ To me, that’s an acceptable mortality rate. The healthiest one is the $10 sapling I bought on sale in a Home Depot parking lot. I think it thrived because I planted it in a sunnier spot than my other (more expensive) redbuds, where it also happens to get watered by the next-door neighbor’s lawn irrigation system. As the realtors say: Location, location, location.

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