Monday, May 16, 2011


Ah, rain – the balm for tired gardeners’ muscles! There’s no better excuse to curl up with a gardening magazine for a few hours. But, once rested, it will be tempting to head out during the lulls to pull weeds. Resist the urge. While the leaves of plants are wet, you might spread fungal disease from one plant to another, just through hand, foot or pant leg contact.

When the plants are dry above ground, get out there and yank some of those invaders. What is a weed? Some define a weed as any plant growing where it isn’t wanted. But there is another category, one that we should be more vigilant about, namely invasive non-native plants, many of which will crowd out everything else in your garden.

The Department of Environmental Protection, doing what its name suggests, adds to its list of Invasive Plants on a regular basis. Sometimes they succeed in outlawing the sale of a plant. It’s a tricky business: take, for example, the barberry.

This prickly shrub has been hybridized widely to make it more colorful. Probably you or one of your neighbors own a few – Ruby Carousel, Rosy Glow and Royal Burgundy are among the purple versions of this originally green-leaved shrub. Barberry has been invading our woods at an alarming rate, replacing native shrubs and seedling trees. It survives not just because of its vigor, but because deer hate its thorns.

The Connecticut Invasive Plant Working Group fingered barberry years ago, but nurserymen were sure that their colorful hybrids weren’t the problem: after all, the woodland invaders have green leaves. Case closed. Further research, employing more sophisticated tools, showed that many of those purple hybrids actually produce the green invasives found in the woods. All it takes is one hungry bird who eats a bunch of berries, then flies into a tree to digest a bit, and pretty soon, you have a well-fertilized bunch of seeds sprouting at the base of that tree.

The upshot, after a long battle, is that the nursery trade has voluntarily committed to stop selling about two dozen invasive barberry cultivars. Many other barberries remain on the market: I advise caution in planting any of them.

But, to get back to the subject of pulling weeds: if you have limited time, focus on the ones that are in flower. After the flower comes the seed, and you want to get rid of that weed before it propagates all over your garden. The weatherman isn’t encouraging, but maybe by Friday you can thwart some of those thugs.


Eye M said...

thanks for the reminder

Anonymous said...

My neighbor has just planted a whole hedge of those darn barberries, after removing 5 beautiful trees from their lightly wooded lot. What landscaper sold him on that plan?

Jam said...

A lovely piece, thanks! My personal nemesis is Purple Loosestrife, and I wish we would take the issue of invasive plants seriously before we lose all our wetlands to this beast! In graduate school I wrote a paper about zoning for allowable plants in the same way we zone for land use. If homeowners and landscapers had a list of what not to plant in specific geographic locations, it would go a long way toward controlling invasive species.

Tree Fanatic said...

Thanks! Purple loosestrife can be controlled with a beetle imported from Europe; it is very specific to loosestrife. Lots of info can be found here:
A good source of info on New England's invasive plants can be found here:

A smart landscaper will belong to the CT Nursery and Landscape Association, and will be proud of his or her certification, which requires regular upkeep.

Anonymous said...

beetle imported from europe? wonder how long it will take before that gets out of control, like the loosestrife.

Tree Fanatic said...

I had serious doubts about the beetle myself, but it is the insect that controls purple loosestrife in Europe. It was studied at length at UConn before it was released in limited trials. Amazingly, they could find nothing the beetle would feed on except loosestrife. It has been used very effectively for over a decade. There are a few that are being used, but the ones I am familiar with are species in the Galerucella genus.
Similar research has been fairly successful in controlling the Hemlock Woolly Adelgid with introduced predators. Many people are unaware of what important research is conducted at UConn and at the CT Agricultural Experiment Station, especially in the area of Integrated Pest Management.