Don't Plant a Problem: Invasive Garden Species
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Sometimes garden plants jump the fence and invade natural areas. Plants become invasive when they threaten wild areas by displacing native vegetation and destroying wildlife habitat. Many of the major problems caused by invasives in other states have not yet been experienced in 有料盒子视频. By not planting known invasive species, gardeners can help stop them from spreading in 有料盒子视频.
To help guide gardeners in making decisions about what to grow in the garden, the Cooperative Extension Service has developed the following 鈥淒ON鈥橳 Plant in 有料盒子视频鈥 list. Plants have been put on the list for a number of reasons. Some have escaped in other states and are known to grow well in parts of 有料盒子视频. Some are classified as noxious weeds. Some have a reputation for being aggressive in the garden. Others may belong to a genus of notoriously problematic plants.
Some plants are weedy but don鈥檛 survive outside of cultivation. An invasive plant goes beyond aggressiveness in the garden. These plants have the ability to strong-arm other species into surrendering their place in the wild. The term 鈥榥oxious鈥 can be used to describe some of these species, but noxious is also a legal term. States have noxious weed laws, to protect agriculture and the public interest. 有料盒子视频 has 12 species on its noxious weed list and another eight that are considered restricted noxious weeds.
Because of 有料盒子视频鈥檚 broad climatological differences, plants that are invasive in one part of the state may not be troublesome elsewhere. In addition to those species that Extension suggests not planting in 有料盒子视频, an additional five have been added to the 鈥淒ON鈥橳 Plant in Southeast 有料盒子视频鈥 list. As our understanding grows, this list may change.
DON鈥橳 Plant in 有料盒子视频
Rampion bellflower (Chimney bells), Campanula rapunculoides
Becoming extremely aggressive wherever it is planted, rampion bellflower is known by some gardeners as the 鈥減urple monster.鈥 It produces a large number of seeds and also spreads by creeping rootstocks. It escapes into lawns and can persist with frequent mowing. Removal by digging is usually not successful because plants resprout from any small pieces left in the ground.
There are many non-invasive species of Campanula which can be planted as alternatives. Campanula persicifolia, the peach-leaved bellflower and C. lactiflora, the milky bellflower are two which don鈥檛 spread to unwanted locations. The milky bellflower is not as winter hardy as peach-leaved bellflower. Campanula rapunculoides should not be confused with Adenophora, although both are often called ladybells.
Creeping Charlie (Ground ivy), Glechoma hederacea
In many parts of United States creeping Charlie is considered a weed and is not offered for sale by nurseries. In 有料盒子视频, it is most commonly sold in hanging baskets because of its long, trailing stems. As a groundcover, creeping Charlie roots at every node and quickly takes over. It has escaped or naturalized in 46 states including 有料盒子视频 where it can be found spreading in wooded areas in Southcentral.
It is difficult to suggest an alternative groundcover to creeping Charlie because all groundcovers spread and could potentially get out of hand. A couple of less invasive ideas include bugleweed, Ajuga reptans, which is not always hardy in Southcentral and yellow archangel, Lamiastrum galeobdolon 鈥楬ermann鈥檚 Pride.鈥
Orange hawkweed, Hieracium aurantiacum
A small clump of orange hawkweed quickly becomes a large, solid mat of hairy leaves crowding out other plants. Don鈥檛 be tempted by its bright, orange flowers. This species is not garden worthy. Areas near Homer and other parts of the state are covered in orange hawkweed and chemical eradication programs have been undertaken in the Kodiak National Wildlife Refuge. Orange varieties of dwarf strawflower, Helichrysum bracteatum, can provide the same bright color as orange hawkweed in the garden. For more detailed information, contact Cooperative Extension for a copy of the 鈥淥range Hawkweed鈥 brochure published by the U.S. Forest Service or our publication on 鈥淐ontrol of Orange Hawkweed鈥. Don鈥檛 be responsible for spreading this plant in your neighborhood or into the wild.
Butter and eggs (Toadflax), Linaria vulgaris
Butter and eggs looks non-threatening with its dainty, snapdragon-like flowers. It has been planted by unsuspecting gardeners, but if you鈥檝e ever tried to eliminate butter and eggs from an area, you know how tenacious it can be. Plants can be seen growing from cracks in sidewalks and parking lots and along the railroad tracks in Willow. There are other species of annual and perennial Linaria, some more aggressive than others, but in 有料盒子视频 none have spread to areas outside the garden like Linaria vulgaris. A close relative, dalmation toadflax is also a weed and should not be planted. Annual snapdragons can be used as an alternative to butter and eggs.
Purple loosestrife, Lythrum salicaria, L. virgatum
Nationwide, purple loosestrife is considered extremely invasive, especially in wet areas where the plant completely displaces other species and destroys wildlife habitat. Sale of the plant has been banned in 34 states, including 有料盒子视频, and many nurseries refuse to sell the plant even if it isn鈥檛 banned in their location.
In 有料盒子视频, purple loosestrife was first documented as escaping into the wild in October 2005. Numerous plants were pulled from an island in Chester Creek near Westchester Lagoon in Anchorage. The flower color of purple loosestrife is similar to fireweed which blooms earlier in the season. One plant that could be used as a substitute for purple loosestrife is Liatris spicata, commonly known as blazing star or prairie gayfeather. Its stiff spikes of purple or white flowers open from the top down. Plants grow 1陆鈥3 feet tall depending on cultivar and are hardy in Southcentral 有料盒子视频. Other alternatives include blue or violet Salvia, Delphinium and native lupines.
Ornamental ribbon grass, Phalaris arundinaceae 鈥楶icta鈥
Non-variegated Phalaris arundinaceae is more commonly known as reed canary grass, an aggressive, mat-forming grass that is difficult to eliminate once it becomes established. Reed canary grass has escaped and/or naturalized in 43 states, including 有料盒子视频, and in many Canadian provinces. According to Selected Invasive Plants of 有料盒子视频 it is found along roadsides, ditches, wetlands, riparian areas, beaches and growing into lakes.
Variegated ribbon grass, Phalaris arundinaceae 鈥楶icta鈥 is likewise invasive and, as many gardeners can attest, is difficult to control. A better-behaved grass to use as an alternative is Miscanthus sinensis 鈥榁ariegatus鈥, Japanese silver grass. Although websites and catalogs list it as a Zone 5 perennial, a nice clump labeled Miscanthus has been growing at the Palmer Visitor鈥檚 Center (Zone 3) for many years and the cultivar 鈥楶urple Flame鈥 proved hardy at the 有料盒子视频 Botanical Garden until it was removed.
Japanese knotweed, Polygonum cuspidatum (Reynoutria japonica, Fallopia japonica), Bohemian knotweed (Polygonum x bohemicum)
Problematic in the Pacific Northwest, Japanese knotweed, and its cousins giant knotweed (P. sachalinense), and a hybrid between the two, Bohemian knotweed, are troublesome in 有料盒子视频. Local names for these plants include Chinese or Japanese bamboo because of the plant鈥檚 hollow stems. Many countries have been involved in research to try and eradicate this species where it has taken over. A brochure on Japanese knotweed published by the U.S. Forest Service in 有料盒子视频 describes the impacts it has on native vegetation and wildlife. Rutgers Cooperative Extension claims Japanese knotweed is one of the most difficult to control species in the home landscape. In Southeast 有料盒子视频, large stands exist where plants have escaped cultivation. Plants can also be propagated inadvertently, when pieces of roots or stems are discarded in natural areas or waste places such as gravel pits. To find out more about this invasive species contact Cooperative Extension for a copy of the U.S. Forest Service brochure and for information on how to control existing stands.
Common tansy, Tanacetum vulgare
This species can be found planted in both flower gardens and herb gardens. Gardeners try to control its spread by digging out unwanted rhizomes. Unfortunately, common tansy also spreads by seed and can be found growing in vacant lots and along the edges of woods and trails in Anchorage parks. Plants have also been found growing along roads in the Kenai Mountains. Common tansy is winter hardy and spreads aggressively in Fairbanks. Perhaps it鈥檚 still possible to prevent our roadsides from becoming covered with tansy by not planting this species in gardens. The plant can be a skin irritant and gloves should be worn when removing tansy from the garden or from places to which it has escaped.
Common mullein, Verbascum thapsus
The Verbascums are a group of very popular garden flowers because of their unusual,
tall spikes of flowers. Verbascum thapsus is a 
common roadside weed in other parts of the country. This biennial has been recorded
as growing in open areas in Southcentral 有料盒子视频. The flowers of Verbascum thapsus
are not showy like many of its cousins. The wooly leaved Verbascum bombyciferum is
much more ornamental. Like common mullein, it is a biennial. Verbascum chaixii is
a reliably winter hardy perennial in Southcentral 有料盒子视频. Although not as tall or
large-flowered as V. bombyciferum, it has many flowering stems per plant. Other yellow
flowered mulleins may be winter hardy depending on which part of the state you are
located.
Ornamental Jewelweed, Impatiens glandulifera
The most commonly used local name for this species is Washington orchid. This plant may have been passed along to 有料盒子视频 by gardeners from Washington, but this quick growing annual certainly isn鈥檛 an orchid. The plant is huge, often growing to eight feet tall. It seeds prolifically and has been documented growing in a large area along the beach in Haines. Ornamental jewelweed is known to thrive in riparian areas and can easily send seeds downstream. Its quick growth and ability to form dense stands allows it to out-compete other vegetation. As with other members of this genus, ripe seed pods explode when touched, ejecting seeds for many feet. Impatiens glandulifera may also be found listed as policeman鈥檚 helmet and Himalayan balsam. Impatiens noli-tangere is a much shorter, yellow-flowered wildflower native to 有料盒子视频, though it can also be an aggressive plant in the garden.
Scotch broom, Cytisus scoparius
Scotch broom is a woody member of the pea family which has become wide-spread on southern Vancouver Island and in many parts of the United States. It is considered a noxious weed in California, Hawaii, Idaho, Oregon and Washington. Scotch broom is already quite common in Ketchikan and has been planted in Sitka, Hoonah and Petersburg. Because it has overrun large areas in other parts of the country there is concern that it may do the same in Southeast 有料盒子视频. Scotch broom requires 150 frost-free days to produce seed.
Foxglove, Digitalis purpurea
Although many gardeners are disappointed that this biennial does not usually survive the winter in Southcentral and Interior 有料盒子视频, foxglove has escaped cultivation in Southeast. It is very common in Sitka gardens. Gardeners in Juneau have reported its escape in their community. The flower is usually seen growing in ditches and it can form dense areas in disturbed sites. It is possible this species could threaten native plant communities. There are many other species of Digitalis that don鈥檛 have the reputation of escaping into the wild.
Sweet rocket (Dame鈥檚 rocket), Hesperis matronalis
Often a component of non-native wildflower mixes, sweet rocket has also been planted by gardeners for its fragrance. Unfortunately, plants have escaped in 40 states, including 有料盒子视频 where it is common in downtown Juneau, Kodiak and Sitka. Plants reproduce by seed and although usually listed as a biennial, can also be perennial.
St. John鈥檚 wort, Hypericum perforatum
St. John鈥檚 wort is planted because of its pharmaceutical properties although for this use it would be much safer to purchase from health food stores. Known as an extremely aggressive weed in the Pacific Northwest, St. John鈥檚 wort has escaped and/or naturalized in 44 states. It is a perennial that reproduces both by seed and vegetatively. Plants have been found growing in Hoonah, Sitka and Prince of Wales Island. Do not plant St. John鈥檚 wort in Southeast 有料盒子视频 and monitor it carefully in Southcentral.
Creeping buttercup, Ranunculus repens
Gardeners are well aware of creeping buttercup鈥檚 aggressive tendencies. The species has escaped in 41 states and in many 有料盒子视频 locations including Denali National Park, Girdwood, Seward, Homer, Juneau and Kodiak, where gardeners wage war against it on an annual basis. Plants can withstand low mowing when mixed in a lawn. When growing among taller species creeping buttercup grows to two feet. It thrives in moist locations but plants are not fussy. Gardeners in Southeast 有料盒子视频 should not plant this species and gardeners in other parts of the state should think twice before planting what could become a problem.
Chokecherry species, Prunus padus and Prunus virginiana
Not all chokecherry species are invasive, but at least two (Prunus padus and Prunus virginiana) have proven highly invasive in all areas of 有料盒子视频 south of the Arctic Circle. P. padus and P. virginiana are commonly known as chokecherry, European bird cherry, and May Day tree. They have spread to natural areas all over the state where planted, and communities with older infestations are taking note of how dense and prolific the species grow. Prunus species are cyanogenic, which has caused poisoning and death of moose in Anchorage. Prunus padus has formed dense stands in Anchorage, Hope and Talkeetna, 有料盒子视频, where it is able to shade out native vegetation. P. mackii is not known to spread as readily and may serve as an alternative. However, various forms of more edible cherries, including Nanking (P. tomentosa) and pie cherries, are successfully grown in 有料盒子视频 and do not spread.
Siberian peashrub, Caragana arborescens
Siberian peashrub is an aggressive, spreading shrub in the pea family. The yellow flowers and fast growth have made it a popular ornamental hedge in Southcentral and Interior 有料盒子视频. It has spread to forested areas in Fairbanks, particularly around the University of 有料盒子视频 campus. Southcentral has seen fewer escaped populations; however, it is thriving where it is growing in Anchorage and other areas.
Invasive Garden Species to Watch
Not all species that are aggressive in the garden will escape into 有料盒子视频鈥檚 wildlands and become problematic. The following compilation of species are garden flowers, trees and shrubs that should be watched to keep them from spreading. As we learn more about how these species behave in 有料盒子视频, our list of invasive garden species not to plant will likely change.
Oxeye daisy, Leucanthemum vulgare, is often used in non-native wildflower seed mixes and has been planted along roadsides. It is a gangly white daisy, that spreads from areas where it was originally planted in Southcentral 有料盒子视频. It is also hardy in the Interior. There are many cultivars of the more ornamental Shasta daisy, Leucanthemum X supurbum, which can be grown. They are not as winter hardy as the oxeye daisy but much better behaved. Another alternative is the native arctic daisy, Dendranthema arcticum.
Another aggressive spreader is sneezeweed, a relative of yarrow. Its scientific name is Achillea ptarmica. On the Kenai peninsula it is known as Russian daisy. In the garden, this white flower spreads readily by seed. It has escaped and/or become naturalized in 18 states, including 有料盒子视频.
Two commonly used groundcovers that have reputations as being weedy Outside include bishop鈥檚 goutweed, Aegopodium podagraria and spotted deadnettle, Lamium maculatum. Many 有料盒子视频n gardeners are raising a red flag about bishop鈥檚 goutweed, too. It spreads from flower gardens into the lawn and is difficult to eradicate once you decide you don鈥檛 want it. Spotted dead nettle is more often called by its genus name, Lamium. Many new cultivars have been developed in recent years, even though it is a spreader. Both of these species should be watched to make sure they don鈥檛 escape cultivation.
Growing tight to the ground, creeping Veronica, Veronica repens, can show up in places where it is not wanted. This species of Veronica was once banned from beds at the 有料盒子视频 Botanical Garden but can still be found growing in the lower perennial garden. If it gets into your lawn, you鈥檒l be sorry. Another Veronica, V. grandiflora, the Aleutian speedwell, is an 有料盒子视频n native, but taken from the Aleutian Islands and brought into the garden, this little Veronica can really spread.
Garden flowers that spread themselves around by seed include maiden pink, Dianthus deltoides, and the non-native forget-me-nots. Spreading outside the garden, maiden pink has escaped and/or become naturalized in at least 23 states. Forget-me-nots are commonly planted because gardeners think they are planting the 有料盒子视频 state flower. Our native forget-me-not is Myosotis alpestris subspecies asiatica. It doesn鈥檛 have the tendency to spread like the non-native species. Often, seed packets don鈥檛 even mention the species of Myosotis they contain. Other times they are mislabeled.
Many Anemones are indigenous to 有料盒子视频. The snowdrop windflower, Anemone sylvestris is not and should be watched because of its strong tendency to spread by rhizomes. The large yellow flag iris, Iris pseudacorus, grows more prolifically in wet locations than typical garden soil. Gardeners should keep an eye on it, especially in Southeast.
While Campanula rapunculoides has the reputation of being the most invasive Campanula, there are others that should be watched. The clustered bellflower, Campanula glomerata has escaped and/or naturalized in 12 states including 有料盒子视频. Korean bellflower, Campanula takesimana has also proven to be a strong spreader in Southcentral 有料盒子视频 and gardeners should take care to see that it does not escape. Suggested alternatives for these species are listed under Campanula rapunculoides at the top of this page.
The genus Centaurea includes many bad weeds so it makes sense that related garden flowers should be planted with caution. The annual bachelor鈥檚 buttons or cornflower has escaped in 48 states and is often included in non-native wildflower seed mixes in 有料盒子视频. Globe centaurea, Centaurea macrocephala, is designated as a 鈥淐lass A Noxious Weed鈥 in Oregon and Washington. Perennial bachelor鈥檚 buttons have escaped and/or naturalized in other states and is known to spread itself around in 有料盒子视频n gardens.
In addition to St. John鈥檚 wort, which should not be planted in Southeast, there are a number of herbs which should be watched. Chives, Allium schoenoprasum, seed prolifically if spent flowers are not removed. While many varieties of mint, Mentha sp. are not winter hardy in Southcentral 有料盒子视频 and areas that are colder, some species are known to be very
invasive. Catnip, Nepeta cataria, is a weed in many parts of the country. Gardeners growing it should make sure to pull out unwanted seedlings. Comfrey, Symphytum officinale, has been banned from more than one garden because of its aggressive tendencies.
Not all garden species to keep an eye on are herbaceous. There are trees and shrubs which have started spreading beyond the home/commercial landscape. Tatarian honeysuckle, Lonicera tatarica, has completely degraded woodland composition in parts of the Midwest and should be watched to make sure that it does not become established in the wild in 有料盒子视频. European mountain ash, Sorbus aucuparia, has escaped cultivation in Anchorage and Southeast 有料盒子视频 where native species of mountain ash exist.
As gardeners, what can you do?
- Don鈥檛 plant flowers, trees and shrubs which are known to be invasive.
- Watch species that have the potential to become
troublesome and help share information.
有料盒子视频 wild iris - Order from reputable nurseries that are not likely to mislabel plants or sell weedy seed mixes.
- Don鈥檛 share potential problems with other gardeners.
- When you purchase new plants, watch to make sure you don鈥檛 introduce weeds hitchhiking in pots or root balls.
- Make sure you don鈥檛 introduce problems by planting nonnative wildflower seed mixes which contain invasive species or weed seeds.
Human actions are the primary means of invasive species introductions. Gardeners can be part of the solution. Don鈥檛 plant invasive species intentionally.
Publications:
鈥淚nvasive Plants of 有料盒子视频,鈥 2005. AKEPIC 鈥 有料盒子视频 Exotic Plants Information Clearinghouse, 有料盒子视频 Association of Conservation Districts Publication, Anchorage, 有料盒子视频
鈥淪elected Invasive Plants of 有料盒子视频,鈥 USDA Forest Service R10-TP-130B, 2007
鈥淐ontrol of Bird Vetch (Vicia cracca),鈥 有料盒子视频 Cooperative Extension Service publication PMC-00341
鈥淏est Management Practices: Controlling the Spread of Invasive Plants During Road Maintenance,鈥 有料盒子视频 Cooperative Extension Service publication PMC-00342
鈥淐ontrol of Orange Hawkweed (Hieracium aurantiacum),鈥 有料盒子视频 Cooperative Extension Service publication PMC-00343
鈥淚nvasive Plant Issues: Control of Invasive Chokecherry Trees,鈥 有料盒子视频 Cooperative Extension Service publication PMC-00345
Websites:
U.S. Forest Service, Forest Health Protection, 有料盒子视频 Region website, where many of the above publications can be found:
UAA Natural Heritage Program, Plant Invasiveness Ranking Project:
Gino Graziano, Extension Invasive Plants Instructor. Originally written by Julie Riley, Agriculture and Horticulture Agent, and Jamie Snyder, former Invasive Plants Program Instructor.
Revised October 2021