Invasive Plants

Gallery and Photos

To reach our gallery of plant images, with links to detailed information, of the major invasive species in Newton, Massachusetts:

Click here to reach the gallery

Other helpful info on Invasive Plants

The links below contain background information on invasive plant definitions, characteristics, how we can and do control them  – and what to plant instead.

What “Invasive Nonnative” means

How Invasive Plants hurt local ecosystems

Ecological Traits of Invasive Plants that make them so successful

Control Methods

What Newton Conservators is doing about Invasive Plants

Get Involved

What to Plant Instead

What “Invasive Nonnative” means

Invasive nonnative (also called exotic) plants were brought here, by humans, from other continents. Here, absent their natural home ecosystems to keep them in balance, they escaped into the wild (became “naturalized”) and are crowding out our native plant species to the detriment of our local biodiversity and ecosystems (plants, insects, animals). Some of these nonnative plants were intentionally introduced for use in agriculture (garlic mustard), horticulture/ornamentals (burning bush, bittersweet, black swallow-wort), medicine, forestry (norway maple for street trees), highway erosion control (multi flora rose), or wildlife enhancement programs (buckthorn). Many were introduced for botanical displays in estate gardens and arboretums.

How Invasive Plants hurt local ecosystems

1. Native plant succession is affected

The continuous growth and spread of exotic invasive plants in native landscapes contribute to the interruption and/or overtaking of some native plant species succession. Most exotic invasive plants exhibit rapid growth and prolific seeding which, in time, creates too much shade for, and displaces, our native plant species that are not shade tolerant.  This action eventually alters affected native plant germination, growth, and establishment patterns of the infested (native) area. For example, glossy buckthorn stands in oak and pine forests (as well as the Cold Spring Park red maple forest) can be so dense that the native tree overstory can no longer successfully reproduce on the forest floor below.  Too much growing space was taken up and shade created by glossy buckthorn for these partial shade-tolerant native species to germinate and grow.  The normal forest plant succession is destroyed.

See “Can the Red Maple Forest Endure” – a Newton Conservators newsletter article – here.

2. Native seed banks are contaminated

When left unchecked, the presence of the exotic invasive plant or plants prove to be a continuous, long-term source of seeds for further invasion of new areas and re-invasion of the invaded area (e.g. the germinating seed of glossy buckthorns take up more space and create more shade which inhibits some light-loving native plants from successfully germinating and becoming established).

3. Ecosystem processes may be altered

These pestiferous plants alter many ecosystem processes including but not limited to plant-soil fertility cycles; decomposition rates of litter layers; soil erosion rates; and water table levels, all of which affect soil food web interactions and populations. Additionally, some exotic invasive plants may hybridize with closely related native species.  Professor Douglas Tallamy, author of Bringing Nature Home and Nature’s Best Hope, describes nonnative invasive species as “ecological tumors” that will grow and destroy local ecosystems, and will lead to local extinction of insect species with snowballing impacts on the food web.

4. Animal population food sources are affected

An estimated 80% of ornamental plants for sale are non-native. This means that the average yard does a poor job of supporting native flora and fauna. By shifting our plantings towards native plants, we can dramatically increase the diversity of bees, butterflies, birds and other animals. Native plants can achieve these benefits: a 50% higher abundance of native birds, a 9 times higher abundance of rare birds, 3 times more butterflies and a 2 times higher abundance of native bees.

Source: Northeast RISCC Management

Ecological Traits of Invasive Plants that make them so successful

Those involved in controlling the establishment and spread of nonnative exotic invasive plants agree that understanding the invasive traits and ecology of these plants will help with the efforts to control them.

1. High seed production and good seed viability

The nonnative invasive species tend to be prolific seeders.  Asiatic bittersweet produces huge numbers of berries/seeds – though  only two-thirds will sprout, the sheer number ensures that bittersweet spreads rapidly. Glossy and common buckthorn are covered with berries and seed.  Norway maple produces huge quantities of its double samaras (two seeds each).  Each Garlic mustard plant can produce thousands of more seeds.

2. Seed is easily dispersed by wind, animals, or water

The seeds of buckthorn, honeysuckle, bittersweet, burning bush are primarily dispersed by birds over great distances. The samaras of Norway maples, fluffy filaments attached to black swallow-wort seeds, and the small seeds of common reed, Phragmites australis, are effectively carried by wind. The aquatic invasive purple loosestrife, Lythrum salicaria, is spread by water currents, as is the rhizome of japanese knotweed (such as occurred in Vermont in 2011 during flooding from tropical storm Irene).

3. Reproduction – often monoecious

Some invasive plants reproduce sexually; the plant requires pollen to fertilize the flower. Sexual reproduction can either require separate male and female plants (termed dioecious reproduction) or involve male and female reproductive structures on the same plant (monoecious). Monoecious plants produce flowers, fruit, and seed on the same plant. Since only a single monoecious plant is needed to start a population, invasives of this type can rapidly colonize and spread into new areas. Most invasive plants are monoecious, which is why they are so threatening to our native ecosystems.

Some of these plants can also reproduce aggressively vegetatively, for example by rhizome dispersal of japanese knotweed during flooding, or resprouting from cut stems of buckthorn, or from bent stems pushed to the ground by fallen branches.  Black swallow-wort and Asiatic bittersweet vine also sprout aggressively from their roots.

4. Seeds have long viability in seed bank

Once seeds are produced, more than half will germinate under ideal conditions. However, not all seeds germinate as soon as they contact bare soil – delayed germination may occur.  Seeds displaying this trait become part of the seed bank, the collection of dormant seeds in the soil of the infested site that can linger until environmental conditions are right for germination at a later point in time. Researchers have found that some exotic invasive species such as purple loosestrife and garlic mustard demonstrate high seed viability: they can persist in soil for many years before germinating.

Be aware at what point in its life cycle an invasive plant produces flowers, fruit, and seed. According to restoration ecologist, Josh Ellsworth (Ellsworth Land Management, Somerville, Mass), “You should always think about seeds when undertaking any invasive plant control project.”

5. Predators avoid them

Most of our native insects and herbivores cannot or do not eat the nonnative species. – it is as if they are made out of plastic.   Some exotic invasive plants have physical structures (spines, prickles, etc.) that deter grazing animals and humans from touching them (such as Japanese barberry).  Other plants produce chemical compounds unpalatable to plant feeding animals (e.g., Japanese stiltgrass, Microstegium vimineum).  As predators avoid the nonnatives, the decreasing supply of native plants is overgrazed further allowing the nonnatives to dominate.

6. Early leaf out and long photosynthesis period

Nonnative invasive plants tend to leaf out earlier in spring and hold their leaves longer in fall.  This longer photosynthesis period gives them an edge over native species, allowing the invasive plants to store more carbohydrates (energy) in their roots. Glossy buckthorn, honeysuckles, garlic mustard, and Japanese barberry exhibit this trait.

7. Shade tolerance high

Seedlings with shade tolerant traits—such as glossy buckthorn, garlic mustard, Asiatic bittersweet vine, and black swallow-wort—can germinate and become established in shady areas. Don’t be fooled; such shade tolerant species can also grow rapidly when the shade opens up due to tree branch dieback, breakage, or fallen trees. However, some exotic invasive plants are shade intolerant and can grow better in sunny areas (e.g., Tree of Heaven).

8. Varied and long fruiting timing

Different invasive plants set fruit at different times of the year, not just in the fall. Many exotic invasive woody plants produce fruits and seeds longer than native plants. Observe when invasive plants set their fruit, so that you can control them before they set fruit (seed). According to Ellsworth, this will give the maximum control for the least amount of effort. In order to control your invasive exotic plants, identify your invasives correctly and review these traits.

9. Broad range of soil and site conditions tolerated

Most terrestrial exotic invasive plants tolerate broad soil and site conditions for germination, growth and development.

Source: Bruce Wenning

Control Methods

Each species has its own characteristics and control methods.  Please see the links and resources on each page on each species for specifics.

Attention, and Vigilence.  The first step in Control is to identify plants and note any new species.  Research each plant – use the  iNaturalist app to help.  Nip any invasion in the bud.  New and spreading species include black swallow-wort (now spread all over Newton), and Mile A Minute vine (we don’t think it’s in Newton yet, but if it is seen here we must report it immediately).  It is much easier (and less expensive) to remove a small norway maple than to wait 20 years until it is a big tree.

In general, plants can be hand pulled, machine pulled, cut, dug up, seeds pulled off, and/or treated with an herbicide.

Hand pulling is good for small infestations, or when the plants are young and small, or when there is a large amount of volunteer labor to do the work.  Handpulling is recommended for the following:

  • garlic mustard (very easy to pull up by the root in spring and summer before seeds are ready to disperse; bag the entire plant and dispose in trash, not in yard waste)

  • buckthorn sprouts/seedlings (pull up by root; ok to leave on site as plant is too young to have seeds)

  • bittersweet small vines (pull up by root and try to get as much of the orange root out as possible; ok to leave on site if no berries)

Machine pulling is done with the help of a “weed wrench ®” that uses leverage to uproot small shrubs and trees.

  • this is effective on small buckthorn and any other small tree or shrub

  • If there are any berries on the tree, remove, bag, and trash them.

Cutting can be done for large infestations, or large plants, where pulling is not feasible.

  • repeated mowing of black swallow-wort is being done by DCR at Hemlock Gorge, in the field at the base of Echo Bridge.  The field is mowed when the BSW is about a foot high and before it sets seed pods in summer.  It is repeated later in season.  This does not kill the BSW but keeps it from spreading further.

  • repeated mowing of garlic mustard can also work, but they will resprout so repeated treatments during the growing season are needed.

  • Japanese knotweed can also be controlled by cutting.  Let it grow about 3′ high, then cut or scythe them (debris can be left on site as there is little rhizome dispersal in this method).  This must be done about 4 times during the growing season, each time letting it get about 3′ high before cutting (this exhausts the rhizome over time as it has put energy into the growing stems).

  • Cutting can be done for large shrubs like buckthorn or honeysuckle, but they will resprout so follow up manual cutting back the respouts is needed.  Again, if there are any berries they must be bagged and trashed.

  • Cutting of large bittersweet vines that are growing up into trees (and will strangle and topple them) is better than doing nothing.  The ettiquette of cutting a vine is to cut it in 2 places – at the base, and at eye level (to make it obvious to the next puller that the vine has already been cut).  Do not try to pull the vine down from the tree; it will soon die and will no longer harm the tree.

Digging up the roots is the best manual way for several plants.

  • Black swallow-wort small infestations should be dug out – dig deep with a japanese garden knife to get out as much of the spaghetti like root as possible.  Small pieces of root and runners will remain and smaller plants will sprout from them, so follow up is needed.

  • Japanese knotweed rhizome can be dug out – bagged and trashed – but the small pieces left will continue to resprout so much follow up is needed.

Pulling off seed pods

  • When digging is not an option and seed pods have formed on black swallow wort, it is better to just pull off the vines and seed pods (and bag and trash them) rather than risk them being dispersed into the wind.  Although the plant will still resprout the following year, this methods still keep many thousands (billions?) of seeds from germinating.

Herbicide use

  • Herbicide use is not permitted in any public area without approval from the city and its Integrated Pest Management committee.  In all cases application of herbicide must be done by a licensed applicator.

  • Newton Conservators does not recommend herbicide use in home yards, as infestations are usually small enough to be controlled by other methods.

Conservation Commission has published a chart of invasive species and recommended control methods.   See it here.

What Newton Conservators is doing about Invasive Plants

In spring and fall we conduct group invasives pulls at many public parks.  This is a great way to do public service and help the planet, and also learn about the species for control in your own yard.

[Link to past and upcoming sessions]

Cold Spring Park Buckthorn Demonstration Area

Invasives removal at Upper Falls Greenway

Woodcock Meadow Restoration:

Education

Get Involved

 Identify the plants in your yard. Here are some articles to help:

Use the iNaturalist app to help with identification:

Come help take care of our public spaces, and team up with Newton Conservators at some of our activities and events.  To join our team of invasives pullers,  contact president@newtonconservators.org.

What to plant instead

Choose native options whenever possible.

For a one-page list of native plant replacements (grasses, flowers, shrubs and trees) with their characteristics and sun/shade/water needs, plus a one-page primer showing the benefits of replacing non-natives with climate-smart plants native to the northeast, see The Northeast Regional Invasive Species & Climate Change Management effort (of which UMass Extension is a part)  which offers this “Climate Smart Native Plants Pamphlet” as a PDF here.

University of New Hampshire has a short list of shrub and tree alternatives  here.

National Wildlife Federation has a Native Plant Finder based on zip code (August 2020 in Beta test) that lists flowers and grasses, as well as trees and shrubs. This tool is recommended by Prof. Doug Tallamy (author of Bringing Nature Home and Nature’s Best Hope).  Find it here.

Further resources

Source – Bruce Wenning

Books about Invasive Plants: (Numbers 1 and 2 should be bought together)

1. John M. Randall & Janet Marinelli, Editors Invasive Plants: Weeds of the Global Garden. Brooklyn Botanic Garden. Handbook # 149, Winter 1996. www.bbg.org

2. C. Colston Burrell; Janet Marinelli and Bonnie Harper – Lore, (editors). Native Alternatives to Invasive Plants. 2006. Brooklyn Botanic Garden Handbook # 185. Brooklyn, N.Y. www.bbg.org/nativealternatives

3. Devine, R.S. 1998. Alien Invasion. America’s Battle with Non-Native Animals and Plants. National Geographic Society.

4. McNight, Bill, N. (Editor). 1993. Biological Pollution. The Control and Impact of Invasive Exotic Species. Indiana Academy of Science. Indianapolis.

Two books to help with Tree and Shrub Identification; old standard college texts.

1. The Shrub Identification Book by George W. D. Symonds. William Morrow Company, New York.

2. The Tree Identification Book by George W. D. Symonds. William Morrow Company, New York.