Watch Out For These Twelve Invasive Plants in Alaska

Be on the lookout for invasive plants on your property in Alaska, like the Japanese knotwood and some particularly nasty thistles.
Written by Amber Reed
Reviewed by Melanie Reiff
Alaska may be known as the Last Frontier, but be vigilant for unwanted plant species trying to make this state their first frontier—like the oxeye daisy, bird vetch, and even the common dandelion.
Alaska is a place of wide open spaces and beautiful, rugged wilderness home to an incredible amount of plant and animal life. Unfortunately, not all of these species are welcome—there are many kinds of invasive plants that take advantage of Alaska's short growing season and can create big problems in a small span of time. 
Be on the lookout for invasive plants if you’re a home or landowner in Alaska. Not only do many of them pose a fire hazard, but they’re also detrimental to native plants, animals, and your property value!
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Twelve invasive plant species in Alaska

1. Common dandelion

Scientific name:Taraxacum officinale
What it looks like: Classic dandelion appearance: green leaves with yellow flowers which turn into cottony puff balls
Why it’s a problem: So, aren’t these considered weeds just about everywhere? Well, yes. But while the common dandelion isn’t the most aggressive of invaders, it’s by far one of the most prolific—particularly in Alaska’s state parks. This bane of lawn owners everywhere can quickly take over a natural landscape in Alaska, and threaten the ability of native species to thrive. 
What to do: If you’ve ever had a yard before, you know the drill: pull them out by the root before they go to seed. Don’t forget to make some wishes with the help of a shooting star or passing leprechaun!

2. Bird vetch

Scientific name: Vicia cracca
What it looks like: Climbing perennial with small green leaves and bluish-violet flowers; can be distinguished from the native species by a curled tendril at the end of each stalk
Why it’s a problem: This nasty and tenacious creeper spreads quickly and easily, and seeds can lay dormant in the soil for up to 5 years. The native alpine sweetvetch is an important food source for grizzly bears, but this invader brings nothing to the table. That identifying tendril at the end of each stalk? The bird vetch uses that to cling to and choke out native vegetation. 
What to do: Hand pulling can be effective for small patches, but larger ones will likely require herbicides. 

3. Bull thistle

Scientific name: Cirsium vulgare
What it looks like: Green rosette-like foliage that looks similar to a dandelion, can grow a stalk several feet tall with a purple thistle
Why it’s a problem: This thistle sends down a long, deep tap root, making it both a pain to get rid of and a drain on water resources for native plants. It spreads quickly, displacing local flora and disrupting foraging for livestock. 
What to do: Hand pulling or mowing is needed for four consecutive years. 

4. Reed canary grass

Scientific name:Phalaris arundinacea
What it looks like: Tall, bluish-green reedy stalks with seed heads that are reddish-purple, then become brown
Why it’s a problem: Like several of the invasives on this list, reed canary grass spreads prolifically thanks to its rhizomes. You know when you’re pulling weeds and find those annoying roots that run parallel to the ground and seem to go on forever? We’ve called them some very uncivilized things while gardening, but their official name is a rhizome. 
What to do: This grass chokes out a host of native vegetation, and the USDA and Forest Service consider it “very difficult to impossible” to eradicate once it’s established. Thoroughly remove any you see as quickly as you can. 

5. Orange Hawkweed

Scientific name: Hieracium aurantiacum
What it looks like: Two to 12-inch green stems, with reddish-orange flowers
Why it’s a problem: Unwittingly often planted by gardeners and wildflower enthusiasts, this pretty but pesky invasive spreads quickly and can form dense mats, out-competing native plants. 
What to do: Plant something like a coastal wallflower or great burnet if you want that lovely orange color. Herbicides are usually needed to get this invasive in check, but hand-pulling can be effective. 

6. Perennial sowthistle

Scientific name:Sonchus arvensis
What it looks like: Very similar to the common dandelion with small yellow flowers on tall stalks
Why it’s a problem: The perennial sowthistle invades gardens and farms, and can cause crop failures by monopolizing resources like water and soil nutrients. 
What to do: Diligent manual or mechanical removal is the most effective method for eradicating perennial sowthistle. 

7. Scotch broom

Scientific name:Cytisus scoparius
What it looks like: Perennial shrub that can grow up to ten feet tall with abundant, bright yellow flowers
Why it’s a problem: Although they may look lovely spread across a hillside or a meadow with their cheery yellow flowers, the scotch broom is bad news. They can grow into dense stands that inhibit natural reforestation, block out foraging land for deer and other wildlife, and create a huge fire hazard. 
What to do: This one’s tenacious—root bits left behind can resprout, and the Forest Service reports that the seeds can stay viable for up to eighty years. Yes—eighty. Multiple and repeated removal methods are often needed for scotch broom management. Pull it up, mow it down, and use an herbicide if needed. 

8. Oxeye daisy

Scientific name:Leucanthemum vulgare
What it looks like: Classic white daisy-like flower with yellow centers on long, thin stalks
Why it’s a problem: Why is it always that the cute ones turn out to be bad seeds? The oxeye daisy is another invasive that, while pretty to look at, causes a lot of problems. These form dense colonies that can cause soil erosion and choke out native flowers. They are not attractive to grazing animals or pollinating insects, but do host several nasty plant viruses. 
What to do: These are frequently found in wildflower seed mixes, so read the labels carefully if you like to plant wildflowers. If you do have them on your property, pull them out completely, place them in a plastic bag, and leave them in the sun for a bit to finish the job. 

9. White and yellow sweetclover 

Scientific name:Melilotus officinalis
What it looks like: Produces shoots that can grow up to 12 inches in length, sweet smelling with many small yellow or white flowers
Why it’s a problem: These plants were brought into North America as a forage crop in the 1600s, and have since spread to all 50 US states. It can form dense patches that crowd out native species and can threaten the ecosystems along riverbanks and in riparian areas. 
What to do: This is another one that really wants to live, and it produces massive amounts of seeds that can remain viable for decades. A few years of diligent hand pulling and mowing before the plants go to seed are needed, and place the removed plants in plastic bags to prevent the seeds from spreading. 

10. Spotted knapweed

Scientific name:Centaurea biebersteinii or Centaurea maculosa
What it looks like: Can grow up to three feet tall from a sturdy taproot, with a single pinkish-purple flower at the end of stem branches
Why it’s a problem: This invasive species is dispersed by seeds and can be spread by people, animals, crop seed, soil, and contaminated hay. According to the USDA, the spotted knapweed is responsible for millions of dollars of economic loss and environmental damage in the western US. 
What to do: Spotted knapweed is difficult to get rid of once it’s established, so early detection is key. Hand pulling of small patches is effective, but make sure not to disperse the seeds in the process. Removed plants should be incinerated or bagged and taken to a waste collection facility.

11. Japanese knotwood

Scientific name:Polygonum cuspidatum
What it looks like: Hollow, bamboo-like stems up to ten feet tall with broad oval leaves; produces small sprays of whitish-colored flowers in August and September 
Why it’s a problem: The Japanese knotwood forms dense stands of plants that shade out other native vegetation. It’s often found on stream banks and beach meadows, where it damages the ecosystem and reduces the quality of the habitat for animals, fish, and insects.
What to do: Removal of Japanese knotwood is very labor intensive. Hand pulling can be successful for small patches, but mechanical removal and herbicides have a better chance of getting rid of large areas of growth. Studies have shown that herbicides must be repeated four times yearly for several years to fully eradicate this invasive plant.

12. Canada thistle

Scientific name:Cirsium arvense
What it looks like: Can grow up to five feet tall, with rigid, branching stems; flowers are purple-pink thistles that appear on the end of the stems
Why it’s a problem: First of all, let’s clear the good name of our neighbors to the north (or east, if you’re in Alaska).  The Canada thistle isn’t from Canada at all—it originally comes from Europe. This thistle takes out surrounding vegetation by outshading it and produces chemicals that inhibit nearby plants. It can cause scratches and infections in animals and restricts the recreational use of land. 
What to do: This one is also very difficult to get rid of, so the earlier you can identify it and remove it, the better. For a good dossier on both the Canada and bull thistles, check out the Forest Service’s guide to
invasive thistles in Alaska
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How to save on homeowners’ insurance in Alaska

These nasty little invaders not only pose a threat to the native plants and animals in Alaska—they also present a variety of dangers to homeowners. Scotch broom can be a fire hazard, and persistent and thorny invasives like the Canada and bull thistles can potentially lower your property value. 
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