By: Mary H. Dyer, Credentialed Garden Writer
Aster is a huge genus of plants that encompasses an estimated 180 species. Most asters are welcome in the garden, but some species are pests that spread aggressively in certain conditions. Read on for more information about troublesome aster plants in gardens.
Asters that spread aggressively include hoary aster (Dieteria canescens), a low-growing aster that has invaded certain areas in the western United States. While the plant isn’t on the federal invasive and noxious plant list, it is considered to be a problematic plant that easily becomes weedy in dry areas, including pine forests, chaparrals, and deserts.
White wood aster (Eurybia divaricate, formerly Aster divaricatus) is a rambunctious plant that spreads by underground rhizomes. While this hardy plant makes an ideal ground cover and often causes no problems, it can become weedy in some circumstances. Plant this wild woodland aster where it has plenty of room to spread.
Another wild aster by the name of annual saltmarsh aster (Symphyotrichum divaricatum) is one of the worst offenders – an obnoxious little plant that creates problems for homeowners across the United States. You can spot wild aster by its small, daisy-like flowers that pop up in unwanted areas, especially lawns.
Hand-pulling is the most effective method of controlling aster. Pulling is easiest when the soil is moist.
Manual control may not be practical if the plant has spread extensively. In this case, you may need to use a post-emergent herbicide created specifically for broad-leaved plants. When applied correctly, the herbicides will kill the weeds but leave the lawn unharmed. Again, check with your local cooperative extensive office if you’re not sure what product to use.
Pre-emergent herbicides that prevent weeds from sprouting are another possible means of controlling aster in your lawn. Use extreme care and purchase a selective product that kills broadleaf weeds but not turfgrass.
Some people have good luck with corn gluten, a pre-emergent, organic herbicide that works by inhibiting germination of wild aster, crabgrass, and other lawn invaders. It only works when seeds haven’t yet germinated. This product nets mixed results and may require repeat applications.
Most asters are well-behaved, but if you’re concerned about planting an aster thug, check with your local cooperative extension office. They will be happy to tell you about plants that may become invasive in your area.
Be careful about purchasing asters at big box stores, which sometimes stock plants that aren’t well suited for the local growing conditions. Instead, purchase plants at local nurseries and greenhouses.
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I used to be innocent. I used to be trusting. When a neighbor said, "Would you like some of these black-eyed Susans?" I never hesitated to plant them in my own garden. Now, being wiser and more disillusioned, I understand the universal truth: that when a gardener has large amounts of a plant she is eager to give away, there is usually a reason.
There are several different flowers often called black-eyed Susan, but I have figured out that mine are probably the popular variety Rudbeckia fulgida 'Goldsturm'. It is sometimes also called the orange coneflower (although many people consider the only true coneflowers to be the members of the related genus Echinacea, and the cultivar 'Goldsturm' isn't orange. The "true" black-eyed Susan is the closely related Rudbeckia hirta, which is also sometimes called the ox-eye daisy though it is not, of course, a daisy.
The rudbeckias and echinaceas are both perennial members of the aster family, which also includes chrysanthemums, daisies, sunflowers, and of course true asters. While it may be difficult to tell the rudbeckia species apart by their flowers, the form of the leaves is different. R. fulgida (left) has long, teardrop-shaped toothed leaves, dark green in color, sometimes tinged purple the leaves of R. hirta (right) are paler in color, more narrow, less toothy, and leaves and stems are hairy.
Because the Rudbeckias are native plants of North America, some people will say I can not properly call them "invasive" here. Fine, but they certainly do spread! While they seed themselves, they spread more readily by runners that sneak along just below the surface of the earth, popping up new plants every couple of inches. These new plants are insidiously tiny above ground, hard to spot and harmless-looking at first. But they are rooted quite tenaciously and do not willingly let go of the earth. Before long, each one is firmly established and sending out new runners of its own.
Of course the defenders of rudbeckia would say that you want a desirable plant to spread, and, to an extent, this is true. When I accepted these plants from my friendly neighbor, I was happy to find a plant that would flower later in the year. The section of the garden where I put them already had painted daisies, which make a fine show in May and June but die back in the mid-summer heat. Rudbeckia follows them quite effectively. The bright gold flowers are attractive and stand for weeks, providing bloom for the rest of the year, into fall.
If only they would stay where I put them, the way the painted daisies do! If only they wouldn't insinuate themselves into the roots of the other plants! If only they were more easily pulled out when they do! But no, so there you can find me on my knees with my garden paring knife, carefully dissecting out the upstart new sprouts of rudbeckia from the rhizomes of the Zebra Iris. It is at such times when I contemplate the fact that there is far more than one flower calling itself the Black Eyed Susan, and that somewhere is a variety that is just as attractive, blooms just as long, and doesn't spread at quite such a rampant rate. If only I had taken the trouble to find it, instead of taking the neighbor's unwanted plants off her hands.
The next time some cheerful neighbor comes offering me excess plants, I hope I will remember that there is probably a reason why she wants to get rid of them.
(Editor's Note: This article was originally published on April 29, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
Purple coneflowers grow well just about anywhere in USDA hardiness zones three through nine, but in colder climates, you may want to give them a little winter protection in their first year. However, once established, coneflowers are rugged and hardy.
Coneflowers grow well from seed and can be divided to make new plants. They can also be grown from stem cuttings, but often with less success. They're easily found in garden centers and can also be purchased via mail order. Coneflowers start blooming in early summer and will repeat-bloom throughout the first frost. They may take a break after their initial bloom period, but they will quickly set more flower buds.
To get the most blooms (and the sturdiest plants), plant your purple coneflowers in a spot that gets at least six to eight hours of full sunlight each day. The plants will tolerate partial shade, but may eventually flop over, and the blooms won't be as prolific.
Coneflowers grow best in a garden that boasts a neutral soil pH of about 6.5 to 7.0. They can thrive in a variety of soil types, including sandy, rocky, and clay soils. However, they do not like wet or mucky soil. For best results, add a bit of compost to your mixture when planting to give your coneflowers successful a good start.
Coneflowers are often listed as drought-tolerant plants, but they will actually do much better with fairly regular watering. Water them daily just after planting, then transition to an inch of water per week for the rest of the plant's first year of life. Second-year and older plants may only need watering during droughts.
As a native prairie plant, purple coneflower thrives in hot, dry climates but can handle a range of temperature and humidity fluctuations. However, they do not do as well in very humid climates, or in rainy areas where the soil stays wet.
Although coneflowers thrive best in a soil high in organic matter, too much supplemental fertilizer can cause them to become leggy. Adding compost each spring usually gives them the nutrition they need for healthy foliage and blooms.
Every three to four years, you should divide your asters to keep them from growing too large, American Meadows recommends. Do this in spring after the ground thaws, and the plant has started to grow. Either divide the plant into roots of 6 to 8-inch in diameter, or separate parts of the roots from the main plant.
Replant the divided plants right away, and water them deeply after planting. Plant asters in full to partial sun, but if you live in an area with hot summers, plant your aster away from an area that gets full midday sun. Asters can also grow from seeds, but the process to mature into an aster that produces flowers can take several years.
Dividing asters every three years or so will help prevent powdery mildew disease, one of the few pests that affects asters. When planting, make sure you give them room to prevent their leaves from becoming crowded and ensure air circulation, which will help prevent powdery mildew from becoming a problem.
We just spent an incredibly long time clearing out our yard and getting rid of plants that got away from us. We have a fresh start on a small 1/4 acre lot and I am trying to go as native as possible without creating any maintenance problems for us.
I would love to add joe pye weed, asclepias, native asters,liatris, and echinaceas. I just want to make sure before I add them, that they are not going to eventually become a problem for us. A problem for us would be if they reseed tremendously, if they outgrow their predicted space and encroach on neighboring plants, if their root system makes it difficult to remove the plant, especially if when you attempt to dig it out, any root you miss, turns into another plant.
What would be okay for us. if we have to divide them maybe every 4 yrs, if they gently reseed, if they increase in size at a slow to moderate rate, without taking over the yard. If they can easily be dug out and given away if they don't work out for us.
Can someone share their experiences with these native plants?
Oh, I was also going to try to add Little Bluestem grass and wonder the same questions as above?
i have seen some asters get out but i dont think they would be a very big problem to remove.
I have recently done the same thing on about 2/3 acre. My design came from a professional who specializes in natives and natural landscaping. All of the plants on your list are in my new yard except the Joe Pye Weed. I can't say if that is more because of its cultural requirements that hte yard did not meet or because it would not be a good choice for my goals. My goals were. native as possible, reasonably civilized so the neighbors are not appalled, habitat for birds, small mammals, encourage hummingbirds and butterflies and above all else, after the garden is established it must be virtually maintenance free. I like the idea of a garden but not hte gardening. So I have lots of groundcovers so there won't be weeding. Things like that. As to the plants he chose. in some cases they were smaller versions of the species depending on where they were going. ie Kim's Knee High rather than the species. As to Asters, he chose Aster Oblongifolius "October Skies". I think it may be a bit more restrained than some others.
I grow all of the plants that you mentioned.
First of all we should define invasive. None of the plants are invasive as in detrimental to agriculture or natural habitats.
You are more concerned with "aggressiveness" in the sense of a landscape or garden.
All of the plants you mentioned have extensive root systems. However, if you want to remove them, you can dig the core of the roots out and missed roots will not resprout. Its the extensive root systems of these plants that make them desirable, drought resistant, disease resistant, they won't need soil amending or fertilizers etc.
Little blue stem tends to spread and cannot be divided without a saw. its does widen and spread, but slowly .
The rest of the plants do widen as they grow and they will tend to fill in the space that they are given.
The grass (LBS) is recommended to fill in between the flowers because without the competition from the grass the flowers tend to get top heavy, wide and fall over. The grass interplanted with the flowers helps keep them from falling over. (my observational opinion)
The asters tend to reseed readily and some species are considered aggressive. It depends upon the species and your growing conditions. (This can easily be controlled by dead heading the flowers not letting the seeds hit the ground. )
Some of the aslpeias spread readily too, depends upon the species and your soil conditions. Asclepias are quite lovely and make excellent landscape plants. I think they can be controlled fairly easily by snipping the seed pods before they open.
If you do plant those plants, get ready for lots of butterflies. All of those plants are butterfly favorites and you will enjoy both the beauty of the flowers and butterflies.
Most of the plants you list will possibly spread by seed (Aster, Echinacea, Liatris) and/or by runners (Asclepias). With the exception of common milkweed (A. syriaca), none of them are invasive by my standards. They tend to fill in gaps in your planting, producing a more naturalistic look (which I like). They may encroach or overtop smaller species.
Most asters do get large and they will spread by seed if they like your conditions. Joe-pye weed can get HUGE. Both of these can be maintained at a smaller height by cutting them back by one-third to one-half early in the season. My asters are due for a haircut this weekend. This year I will experiment and let my Joe-Pye grow as tall as it wants. It is about six feet tall already and flower buds are barely visible.
I think john mo's post is an excellent example of different soil and growing conditions. In my yard, its the asters that get HUGE and get a trim, while joe pye is left to grow at his own pace, the joe pye spreads but not as quickly as the asters or culversroot.
Gee thank you all so much for all the great input.
philmont. thanks for sharing your experiences with asters. I am happy to know if they do reseed they can be pulled out easily.
Robin, that is very encouraging that your professional chose these for the goals you specified. I would have had similar goals so I was happy to hear that.
Joe. thanks for defining invasive..yes you are correct, I am more concerned with aggressiveness. I am relieved to hear that if I need to take them out, missed roots will not resprout. With the reseeding. I guess I could control the extent of the reseeding by deadheading some or most of the flowers.
John. I hadn't thought about keeping them smaller with pinching. I am hoping to try to let them grow as they like for one year but it is good to know that I could get a different result with pinching if I wanted to.
Lots of help here, thanks very much in helping me to think through how I can accomodate these great plants in my yard.
I enjoyed reading all the postings and they tend to go along with my experiences, both in my home garden and as a professional for the past 10 years. I also cut some plants in half or thirds--especially around my front door--rosin weed (for example) is very pretty and well behaved when treated this way.
The natives that I usually avoid because they are too aggressive here in Kentucky are Ratibida (grayheaded coneflower) almost all coreopsis--(one exeption--I like the tall coreopsis--true to its name is is tall, but not outwardly bound) and the grass that people call sea oats-- it spreads everywhere when given a chance. If you avoid those, the rest are slow enough in growth for you to get to know. Some people have problems with ashy sunflower, but I haven't. Good luck and have fun with your native plants--you will love the birds and butterflies you will attract!!
I have found that Cup Plant, Silphium perfoliatum, is extremely aggressive in my loamy-sandy soil. I get HUNDREDS of seedlings every spring, tough sneaky little buggers too! The Mother plant is easily three feet across and twelve feet tall at flower, and the birds go bonkers over the seed. I've tried pinching it back to shorten it and and it didn't do very well cosmetically. Although I consider this plant in the way high maintenance category, it is too magnificent not to include, just be warned.
Thanks for your input too. I am determined to provide as much for the birds and butterflies as I can and to use as many natives as I can, but have to keep yourself on track to be able to care for it all. So it is important to know what you are in for. Pam, I couldn't give that Cup Plant that kind of maintenance so I really appreciate having that information. Although I wasn't considering using it right now, who knows, at some point I might have been. I have seen the plant and it is really a great plant.
I also have had enough experience with coreopsis to know how much of it I can contend with, and after having read a number of posts on the problems with sea oats grass, I have thankfully stayed away from that one.
Yes, I am looking forward to the birds and butterflies.
Make sure you put a shallow dish with water, or better yet fill it with sand, THEN water, for the butterflies to get a drink without drowning. I also put rocks (some low, some high) in a regular ground birdbath for the smaller birds - and so no one gets trapped.
I have aromatic aster and false aster that have tripled in size in one year. Wish my butterfly weed had done that!
I'd just like to say that my garden has many of the plants you list, and they all reseed. In fact, about half of the "weeds" I get are in fact volunteers of my flowers and need clearing out. On the other hand, this gives me lots of seedlings to move around if I want, and sometimes the spots they choose are better than the ones I choose for them. One reason I enjoy gardening with native species.