Invasive plants


Masses of white flowers are a common and beautiful sight along Connecticut’s roadways and in fields this time of year (late May through June). While there are (of course) many shrubs and trees bearing white flowers, one of the most predominant is multiflora rose (Rosa multiflora).   This rose is native to Japan, Korea and parts of China and has become invasive throughout eastern North America.  While it is invasive and is a real problem, we’re sort of stuck with it overall so go ahead and enjoy the gorgeous blooms.MultifloraRoseBush.JAllen  Photo: J. Allen, UConn

Multiflora rose was first introduced into the U.S. as early as 1866 for use as a rootstock for ornamental roses. In the 1930s, the U.S. Soil Conservation Service began to recommend it for erosion control and as a ‘living fence’ for livestock.  In the 1960s plants were even distributed to landowners for free to encourage planting as cover for wildlife including birds and rabbits and as a food source for songbirds.  Thanks to the songbirds, many seeds have been distributed to new sites because they do like to eat the nutritious rose hips (fruit).   The plant is now considered a noxious or invasive weed in many states including in Connecticut “…prohibited from importation, movement, sale, purchase, transplanting, cultivation and distribution under CT General Statutes §22a-381d”.

MultifloraRoseflowers.J Photo: J. Allen, UConn

It’s pretty easy to recognize multiflora rose when it’s in flower but also once the bloom period is over. Flowers are borne in clusters of mostly white but sometimes slightly pink flowers that are ½ to 1” across and have five petals.  Leaves, too, are distinctive.   They are alternate and compound, having 5-11 oval leaflets with toothed margins.  The base or petiole of the leaf is fringed.  Even the thorns are unique to this species.  They are large, curved backwards and have an oval base.  If a thorn is removed, it will leave a visible oval scar on the stem.  They’re pretty serious thorns and are reported to be capable of puncturing tires and leaving a painful gash in skin.  Overall, this plant can reach a height of about 15’ with long, arching stems.  It can also be a climber and at times you will see it spreading up against other vegetation or structures.  For some great info and photos of the thorns, fringed petals (stipules), and more check out this web page:

MultifloraRosespreading.J.AllenMultiflora rose spreading through a natural area and up another tree in the background. Photo: J. Allen, UConn.

Reproduction is by seeds (prolific at 500,000 to a million seeds per large bush per year), suckers and by rooting at the end of stems that arch over and touch the ground. Widespread dispersal is via birds that eat the fruit and expel the seeds.  It’s reported that seeds which have passed through a bird’s digestive system germinate more readily.  Invasiveness is enhanced by not only the huge potential for seed production but also by the fact that the seeds can remain viable in the soil for up to 20 years.

Like other roses, the hips and other plant parts (leaves and flowers) are edible. The hips are high in Vitamin C, carotene and essential fatty acids.  It’s recommended to harvest after the first frost when berries are softened and sweet.  They can be eaten raw but do contain some hairs between the flesh and the seed that can cause irritation.   Leaves, flowers and hips can be used to make tea.  To make rose hip tea, mash the fruits and steep in hot water.  Leaves are best when young as the hairs on the undersides can become stiffer and less palatable later in the season.

Some of the broader impacts of this plant, like other invasives, include displacement/replacement of native plants and the resulting impacts on habitat and food supply for native wildlife. Pasture lands are adversely affected when these thorny plants encroach and reduce forage area for livestock.  Even forestry operations are affected because of the impenetrable, thorny thickets that form, reducing access and making work difficult.  Multiflora rose can thrive in a wide range of habitats from open sunny sites to woodland edges.  It can survive on a range of soil types but is not found in extremely dry or wet sites.

Control methods used include physical or manual removal including mowing, digging, and prescribed fire. Chemical herbicides can be used as either a cut stem (fall) or foliar application.  Biological controls are not yet available.  A virus that causes rose rosette disease limits growth in some areas but that also affects ornamental roses.  An insect, the European rose chalcid, is being studied for potential use.

By J. Allen


Comfrey flower, photo by C. Quish

Comfrey flower, photo by C. Quish

Not all pretty flowering plants in small, four-inch pots siting on the nursery bench are as innocent as they appear. Beware the sneaky aggressor! About five years ago the delicate and rare clear blue color of the comfrey blossom, shyly wooed me into taking it home. What could one more plant hurt in the side garden abutting the wild side of the neighbor’s yard hurt? Well, it hurt plenty. I have been cursing the day I planted it.

Comfrey gone wild. photo by C.Quish

Comfrey gone wild. photo by C.Quish

Comfrey spreads incredibly fast. It is a hardy perennial with a deep and extensive root system. And its seed drop and are spread to create new plants elsewhere. The neighbor loves it and encourages its spread which doesn’t help my eradication efforts on my side of the property line. I suppose it makes a better fence than wood and nails, and he enjoys the view.  The bees enjoy the flowers, too. Dozens of honey bees can be found busily entering flower after flower, not caring how close I get to almost petting them.

Bee feasting inside comfrey flower. photo, C.Quish

Bee feasting inside comfrey flower. photo, C.Quish

Comfrey is botanically known as Symphytum sp. and is a member of the borage family. The Latin name means ‘grow together’.  It was first brought to America with the English as a healing herb. I contains a high level of the chemical allantoin which aids in cell formation, healing. It also is reported to contain pyrrolizidine alkaloids, known to cause liver damage when taken internally in large amounts. The leaves can be crushed or bruised to be placed on external skin areas to heal wounds and broken bones. I only use the plant as an ornamental and to spread into the neighbors neglected ‘wild’ area.

Comfrey has a tap-root, growing about 18 inches deep in the soil. It does a great job of breaking up compacted ground, accessing the minerals and nutrients out of reach of shallower plant roots. For this reason, comfrey leaves are a great addition to the compost pile, as those deep-seated nutrients of the ground are now taken up by the roots to be stored in the comfrey leaves. Once the microbes in the compost pile break down the comfrey leaves into its basic chemical elements, the nutrients are released into the compost and made available for use by other plants. Just don’t put any of those spreading roots into the compost pile. Keep any seeds out of the compost also.

So heed those enticing words on the plant labels when the just mention the words, ‘fast grower’ or ‘spreading’. Sometimes they really mean it!

-Carol Quish



Queen Anne’s lace or wild carrot (Daucus carota) is native to parts of Europe and Asia and is naturalized in North America and Australia.  It is a biennial in the family Apiaceae.  Domestic carrots are cultivars bred from its subspecies D. carota ssp. sativus.   Being a biennial, it grows a leafy mound of green fern-like foliage the first season and then produces flowers the second year.  Flowers are produced from June through August. The tiny white flowers are borne in flat to slightly rounded clusters called umbels.   Before they’re fully open, the flowers may have a pink to reddish caste.  In some umbels, there is a single dark red flower in the center.  This is said to be a droplet of blood where Queen Anne pricked her finger while making the lace.  The function of the red flower is thought to be an attractant for insects.

The root of the wild carrot is edible when it is young but becomes woody and unpalatable as it matures.  As early as 2000 years ago the crushed seeds were used as a contraceptive.  Research has somewhat supported this; in studies with mice wild carrot was found to disrupt the egg implantation process.  It is not recommended here to use wild carrot for this purpose!

Wild carrot has a poisonous look-alike plant, poison or water hemlock, so it should never be consumed  unless it is absolutely certain that it has been identified correctly.   The leaves of Queen Anne’s lace can cause irritation known as phytophotodermatitis.  When the sap from the leaves gets on the skin and it is then exposed to sunlight, a rash may develop.   This plant is considered a noxious weed by the USDA because of this and because it is a pest in pastures, displacing desirable native plants.

Queen Anne’s lace is also a beneficial plant because it can help attract insect parasites and predators of pest insects to the garden.  Beneficial wasps, ant lions and green lacewings either feed on the nectar or pollen of the flowers or are attracted to aphids on the flowers.

Many animals use the wild carrot plant as a source of food or shelter.  Some that use it as a food source include the eastern black swallowtail butterfly, honeybee, green stinkbug, differential grasshopper, golden northern bumblebee and green lacewing.  Many animals use it for shelter including the eastern black swallowtail, aphids, dog ticks, Chinese mantid, American goldfinch, black and yellow argiope, eastern bluebird, green stinkbug, eastern mole, differential grasshopper, northern mockingbird, common grackle, green lacewing and chiggers.   Other plants commonly found growing with wild carrot include goldenrod, milkweed, pokeweed, smooth crabgrass, red clover, English plantain, devil’s beggar-tick, spotted Joe-pye weed, lamb’s quarters, common ragweed, jimsonweed, black-eyed Susan, Kentucky bluegrass, wild strawberry, and common mullein.

J. Allen

Nope, not Oster, Waring or Hamilton Beach, these are plants that are called into service for the purpose of unifying a planting of individual elements and to give it coherence. Homeowners and professional garden designers devote hours to planning landscapes that will be interesting and attractive throughout the growing season and beyond.  Much is attention is given to the “bones” of a garden –  plants that provide structure and give the landscape interest into the bleak mid-winter. Secondary plants contribute the seasonal interest, texture and rhythm. Then there is a third tier, those varieties that serve the valuable function of tying the whole composition together.

Poppy 'Queen Alexandra' and Cranesbill, McInnis photo

Annuals that self-sow are often the star performers in this category; they can be selectively thinned or transplanted for the desired effect.  They run the gambit from the delicate and well-behaved Nigella to downright coarse and aggressive – the purple form of Perilla, for example. Cosmos and cleome contribute cheerful interest toward the back of a border and will soften the heavy appearance of shrubs. Each plant weaves its unique character through a planting, often with a result that looks more carefully planned than it really was.

Purchased annuals can be used to achieve the same informal effect. Since contemporary gardens rarely adhere to the rigid formality of Victorian carpet bedding designs, weaving annuals through established shrubs and perennials is an attractive way to display their assets, prevent them from flopping, and create a lush display. These workhorses provide a long season of color, and when they do fade, tend to drop out of sight.

Many perennials will return in the spring with a new generation of seedlings in tow. The list is endless, but some personal favorites are: Verbena bonariensis, pops of purple bloom randomly scattered about; Bronze Fennel (Foeniculum vulgare ‘Purpureum’) with its gossamer smoke; Rose campion, (Lychnis coronaria) a vigorous biennial well-adapted to hostile sites; Johnny Jump-Ups (Viola cornuta) , always a welcome surprise in the spring; Snapdragons (Antirrhinum majus) and Columbine (Aquilegia canadensis). Remember that plants that self-sow may not always come true from seed, particularly the hybrids. But, an advantage to this is that the undesirable forms can be culled and preferred ones encouraged.

A bed unifier can double as a living groundcover, such as Speedwell (Veronica spicata) or Cranesbill (Geranium sp.) that will allow taller plants to emerge and harmonize.

Dense groundcovers, such as the sedums, Moss Phlox (Phlox subulata) and Dianthus species serve as a living mulch that discourages weeds and add interest.

Liatris emerging through sedum, McInnis photo

Then there are the happy accidents; the bird-delivered False Solomon’s Seal (Smilacina racemosa), the Lady’s Mantle (Alchemilla mollis) that arrived as a stowaway in a container-grown hydrangea, or a Joe Pye Weed (Eutrochium purpureum) whose seeds were deposited by October breezes the previous year. Consider keeping these volunteers who are already thriving in conditions they themselves have chosen.

A word of warning – some species in some locations cross the line from welcome additions to the party to obnoxious trespassers. Some consider Perilla a noxious weed, for others it’s a simple matter of pulling unwanted plants and cooking them in a Japanese-inspired stir fry. Over time, Rose campion or Bugleweed (Ajuga reptans) can consume a bed, invade a lawn, snuggle into the cracks of a sidewalk and from there scout out new locations to conquer.

Ajuga invading a lawn, McInnis photo

What about mulch? For this gardener, mulch (natural color, PLEASE – and NO cocoa mulch – it’s lethal to dogs!) is merely a temporary placeholder to discourage weeds and add organic matter to the soil while the surrounding plants are filling in.

James McInnis

Spring has finally made her appearance after a very long winter. Shockingly warm days this past week has made leaves seem to explode in the landscape. Along with the flush of green in the lawns and bursting leaves on the trees and perennials, is the return of two unwanted pests: the lily leaf beetle and garlic mustard.

The lily leaf beetle larva from last year spends the winter in the soil as a pupa changing into the adult beetle form sometime during the unseen underground respite. As the soil warms and the lilies poke up from the soil in the spring, the lily leaf now adult beetle comes out also. The beetles will begin to feed on lily leaves. They will also mate after which the  female will lay eggs on the under side of the lily leaf. Eggs will hatch in a few days into a cream colored hump-backed grub. The grub will begin to feed on the lily leaves. Here is the gross part; when the grub poops, it will pile the excrement on its back. This is a protective measure so birds and other predators will not want to eat it! It seems to work as I find no predators eating the poop covered immature in my garden. Once the grub has grown large over a 16 to 24 day period, they drop to the ground to pupate. Adults emerge 16 to 22 days later, feeding on mostly lilies and sometimes on frittilaria, lily of the valley and a few other plants. Lily leaf beetles will only lay eggs on true lilies and larva will only feed on true lilies also. Daylilies are not true lilies and not a host for larva or adult lily leaf beetles. Control measure are handpicking all life stages or spray neem oil on the larva.

LilyLeaf Beetle, (

Larva covered in excrement, (

Garlic mustard is a very prolific and invasive weed. It is blooming now, showing off its many white flowers, producing incredible amounts of seed later in the season.  It is believed that the European settlers brought the original plants or seeds with them here as a food or medicinal source in the 1600’s. It has become nuisance along roadsides and un-mowed areas. Garlic mustard is a biennial, producing low rosettes of leaves the first year and shooting up two to four feet with a flower stalk the second year, then the plant dies leaving a multitude of new seed to germinate in subsequent years. What makes this plant particularly obnoxious is its ability to stop growth of virtually all surrounding plants growing nearby, displacing the native plants and diverse food sources for many animals. Control can be had by continued hand removal or herbicides. Glyphosate is the recommended chemical herbicide.

– Carol Quish

Garlic mustard,

First year garlic mustard plant

Garlic mustard


The numerous extremely warm days of late have pushed the progression of spring flowering bulbs, trees and shrubs. The crocus have come and gone, early daffodils are already fading, magnolias, ornamental cherries, pears are in full bloom, and it is just the second week of April.

Early flowering of fruit trees is a problem for orchardists as there is the likelihood that frosts might follow and affect their crops.

 Frost damage is not a worry for many New England invasive shrubs and trees.  In their race to leaf out before the native woody plants, many  invasive are already producing a green haze, forming a dense understory thicket which can restrict native plant growth and tree seedling establishment.  They not only leaf out early and are not impacted by frosts, but many continue to grow late into the fall, giving them a competitive edge over native plants.

 The barberries are already in full leaf in the deciduous woodland that borders a swamp.  

Japanese barberry April 11, 2010 Manchester, Ct

 Euonymous alatus commonly know as winged euonymous or burning bush in full leaf on the same date.

Euonymous alatus

 Autumn olive Elaeagnus umbellata an invasive that was originally planted for its fragrant white flowers, silvery foliage and abundant red fruit in fall.  It takes over in disturbed areas, is readily spread by birds and small mammals.  

The roots of  autumn olive contain nitrogen-fixing nodules which enhance their ability to thrive in poor soils. They are rapid growers, and produce heavy shade which suppresses smaller plants that require more sunlight. 

Elaeagnus umbellata

                                     Leslie Alexander



Now that the leaves have fallen, an orange cast is visible on trees and shrubs along the roads and in other places.  This is from the fruits of Oriental bittersweet (Celastrus orbiculatus), an invasive deciduous vine.  If you are blissfully unaware of the invasive nature of this plant, you might think these are beautiful.  Well, they are, and that’s one of the reasons this plant was originally introduced into the United States as an ornamental in the 1860s.  Unfortunately, it is invasive, spreading agressively into new areas and killing native plants by covering them or strangling them with its twisting vines.  Its current U.S range includes the northeast and the midwest.

Once you know just how damaging it is, it is really pretty amazing to notice how widespread it is.   In addition to growing on trees and shrubs, it can grow on rocky outcrops, telephone poles, etc.  Pictured is a quite beautiful vine growing on a telephone pole.

Oriental bittersweet vine growing on a utility pole.

Oriental bittersweet can be identified using characteristics of its leaves, bark, flowers, fruit, and root color.  The alternate, glossy leaves are broadly ovate to circular in shape and have toothed edges.  They are 2-7” long and 1.25-3.5” wide.  Small greenish-yellow flowers are present from May to June and are located both terminally and in the leaf axils.  Fruits form in these locations and this habit differentiates Oriental bittersweet from American bittersweet which only produces fruits at the tips of the shoots.  The yellow-orange fruit capsules appear from July through October and open at maturity to expose the reddish-brown seeds.  Bark is light colored and smooth with a few lenticels.  The outer surface of the roots is bright orange and this can aid in confirming identification when pulling young plants. 


Photos from L to R: Columbia Univ., USDA Forest Service, Illinois Dept. of Natural Resources.

Control of Oriental bittersweet is difficult, especially once it’s well-established.  Control measures include pulling, mowing, foliar herbicides and cutting combined with brushed-on herbicides for older vines.  The best time to eradicate this plant depends on the age and number of vines to be removed and/or killed.  Young vines can be effectively controlled using foliar herbicides or regular mowing.  Foliar herbicides are most effective on low growing, dense patches.  Early in the growing season, cut back young plants and allow them to regrow for about four weeks.  Then spray the plants with an herbicide, carefully following all label instructions.   Mowing is an effective method of killing young vines if done weekly.  If mowing is only done 2-3 times per season it actually stimulates vigorous root suckering.  If plants will be pulled, the best time to do this is before fruiting.  If the plants are removed after fruit capsules have formed, bag the plant debris to keep the seeds from being distributed and growing into new plants.  To kill woody, more mature vines, the most effective method is to cut the vine and immediately (within a few minutes) treat the cut stump with an herbicide using a sponge or brush.  The best time of year to do this is late summer.  Vines left hanging in trees will decompose within two to three years.  

 Please don’t be tempted to use Oriental bittersweet vines in decorations on the exterior of your home.  Birds will eat the fruits and the seeds pass through them unharmed to germinate and help spread this plant.  It is also illegal to transport, move or distribute this plant and other banned invasives in the state of Connecticut.  When removing bittersweet plants for control, all plants that have fruits should be bagged and either disposed of in a landfill or left in the sun to bake long enough to kill the seeds.  Help prevent the spread of invasive plants.  Learn more about oriental bittersweet and other invasive plants of Connecticut at or by calling the UConn Home & Garden Education Center toll free at (877)486-6271 or email us at

« Previous Page