Questions on: Dandelions
Ron Smith, Horticulturist, NDSU Extension Service
Q: I was reading through your Web site about how to kill dandelions. However, something needs to replace that space when the dandelions are killed. Will the surrounding grass naturally fill in that space or would it be best to spread some grass seed to prevent new weed competition? If so, when would be the best time to spread the seed after applying the dandelion spray? (e-mail reference)
A: A herbicide treatment followed by a fertilizer application would thicken the grass to fill in the spot. Kentucky bluegrass, which makes up 90 percent of the northern turf lawns, is a rhizomatous grass that fills in bare spots when given a little encouragement by fertilizing, watering and high mowing (2.5 to 3 inches). The dandelions will be out-competed under those conditions!
Q: I have a question about spraying dandelions in our campgrounds. What is the best time to spray and what is the best chemical to use? Is it possible for us to still spray in mid-June and, if so, what would you recommend that we use? (e-mail reference)
A: Everybody wants to spray dandelions in the spring while they easily can be spotted. Some die, but many simply shrug off the dose of herbicide and are around the following year to send out millions of seeds. Give the dandelions a spraying whenever you can in June and again after the Labor Day weekend. Those are the most effective times to get a more complete kill. There are plenty of products on the market. Weed-B-Gone is one of them. It contains a combination of broadleaf herbicide products, which makes it a fairly potent herbicide for controlling more than just dandelions.
Q: I spray my yard with Trimec for dandelion, clover and creeping Charley, but am not sure of the proper formula to use. Could you please advise me on the proper proportions to use? (e-mail reference)
A: All of that information is on the label. If not, go to http://www.pbigordon.com/pdfs/TrimecPlus-SL.pdf for more information. Be sure to follow the directions. Good luck!
Q: I read your column religiously. Would you recommend using Ponderosa pine needles as mulch in perennial beds? Last summer I visited the botanical gardens in Cheyenne, Wyo., and observed they used pine needles as mulch. Also, when dandelions are sprayed or mowed, the blossoms still appear to go to seed. Are those seeds viable? I hope not. (Carrington, N.D.)
A: Using pine needles as mulch is a very acceptable practice. Unfortunately, dandelion seeds are very viable. Thanks for being a regular reader!
Q: Is there any product that can be used in flowerbeds to control or eliminate dandelions after the perennials start growing? I have so many, but some physical limitations prevent me from removing that many by hand. (Jamestown, N.D.)
A: Spot spraying carefully with Roundup is the only alternative I can suggest at this point.
Q: I read that Trimec is good for killing dandelions. The dandelions at my place are interspersed among the tulips. Would Trimec bother the tulips?
A: You bet it would! Wait until the tulip foliage dies down. In late August or early September, use a less potent and soil inactive herbicide to kill the dandelions. Make sure the material does not have dicamba as part of the formula. You will get control of both the mother plants and the newly emerged seedlings.
Q: When is the best time to try to eradicate dandelions? Do I have to spray more than once a year? What is the best weed killer to use? Is it harmful to birds and animals? I notice that birds, especially goldfinches, like to feed on the seed heads. Any other do's and don'ts would be appreciated. (Cooperstown, N.D.)
A: Fall is the best time for controlling dandelions. The plants are going through an assimilative type of growth that will be more receptive to herbicide application. The plants are typically not in flower then, so the birds that feed on the seeds will not be affected. There are many broadleaf herbicides on the market. I suggest shopping around to see which herbicides are specific for dandelion control. Apply herbicide in the early morning hours because the drying sun will help to get the herbicide translocated into the plant tissue more effectively.
Q: I would like to know how late this fall I can spray for dandelions and Canadian thistle and still get effective control. (Lamoure County, N.D.)
A: Itís probably too late if youíve had a killing frost in your area. They will not respond when they have been shut down by cold weather.
Q: My landscaped beds are overridden with thistle and dandelions. There are certain areas of the beds that are infested with thistle and other areas with clumps of dandelions. What is the best way to get rid of these weeds? (E-mail reference)
A: That is a perpetual challenge! Since it is early in the growing season, I suggest the physical removal of them at this time. In other words, create a cleanly cultivated bed with nothing remaining but the ornamental plants that you want. There is a product known as Bio-Barrier that creates both a physical and chemical barrier between the soil surface and the germinating weeds. Place this in your landscape beds after the weeds are removed and cover with an organic mulch like bark or wood chips. You should be virtually weed-free for the next 10 years if everything is done correctly.
A: Here are the facts on dandelions: the young spring leaves are eaten for their vitamin A content and for a diuretic effect. They are mixed in salads, to dilute their somewhat bitter taste (which is prized in Pennsylvania Dutch cooking!). The interesting thing about the diuretic effect of dandelion leaves is that it behaves differently with the body than typical pharmaceutical diuretics. It restores the potassium lost through increased urination. The root can be roasted as a coffee substitute; the flower collected and made into a wine. Will we ever win in the battle against dandelions? I certainly hope not, it may become a major part of our food chain in the future! (Information was gleaned from "The Herbal Drugstore" by Linda B. White, M.D. and Steven Foster. Published 2000.)
Q: I had two smoke trees in my yard that were broke off, one to the ground and the other is about 6 inches tall. All kind of sprouts came up. Will they amount to anything or should I start with new trees?
We planted 13 acres into grass and white clover. Last summer and fall was good growing weather for dandelions. Is there any kind of spray that will kill only the dandelions? (Pelican Rapids, Minn.)
A: Your smoke "trees" are Cotinus coggygria, a plant that is more of a shrub rather than a tree--getting about 10 to 15 feet tall and as wide. Cotinus coggygria is definitely hardy in zone 5 but questionable in zone 4. You must have grown it in a protected microclimate. If it was up to me, I'd let the sprouts take off and see what develops. It will be interesting at least and possibly attractive and functional.
To simply take out the dandelions and not kill the clover, I suggest using 2,4-D. It may toast the clover somewhat, but in my experience it has always come back. Be sure to follow label directions.
Q: The fern peonies here in town have now begun to brown and fall down. Can they be cut to the ground yet? I know the leaves of dandelions that currently are growing freeze over the winter, but do new shoots come from the existing plant next spring? In other words, is it of value to spray and kill the current plants to ward off them reappearing again in the spring? I have red twig dogwoods that have exploded out of control this summer. Beautiful, but drooping with new growth making for difficulty mowing under them. How does one deal with such ambitious growth? It seems to me that certain oaks at the farm produce way more acorns than other oaks of the same size. I think that there are some oaks that produce no acorns, but I could be wrong about that. Any thoughts on this? (Fertile, Minn., e-mail)
A: Cut down your peonies. Spray your dandelions. As for dealing with your dogwoods, the best method is to cut them back to make mowing easier. Not to worry, they are completely winter hardy and will not suffer from a late summer pruning. The other way, tying them up, is a band-aid approach and not very effective or pretty.
And, it is true that some oak trees are more fruitful than others. Sometimes the fruiting is related to the stress the trees are under, as well as the age. Older, stressed trees will tend to fruit heavier, while younger (but still mature enough) less stressed trees will go fruitless or bear very little fruit. Another reason could be hardiness. The flower bud is less hardy than the leaf bud. Hence, the oak that is marginal in hardiness may get caught in a late spring freeze that kills the flower bud, but doesn't harm the leaf bud.
Q: I own an empty lot across from my house and just finished planting about 70 bare-root trees there. My problem is with dandelions. I sprayed last spring and fall, but of course it is impossible to kill them all. I don't dare use 2,4-D with these small young trees. Do you have any other suggestions? (Maddock, N.D.)
A: If you can direct your spray away from the foliage of these young trees, Roundup would do an excellent job killing only the plants whose leaves are hit with it. It has no soil activity and will not be taken up by tree roots.
Q: Last year we lost one of our apple trees to rabbits. We have a seedling that came up from the roots, will this bear fruit? I believe this one was a Harelson. We also have a Red Baron apple tree that half the branches on one side died. It looks like it could fall over, it's so unbalanced. It also has this fungus-like growth. Does this need to be treated? It doesn't seem to affect the leaves or blossoming.
We also have a Habelred apple tree that has a black powder like residue on some of the branches. What is it and should it be treated?
What is the best proven chemical to use to kill dandelions, keeping in mind that we have young children and a dog? (Barnesville, Minn.)
A: The growth from the roots is very likely a rootstock sucker growth. The rootstock is different from the top growth and is likely to result in something unwanted.
The fungus is a saprophyte feeding on dead or decaying wood. The black powder is sooty mold. Pruning to open the canopy of the tree will help to control this superficial fungus growth.
I would encourage you to put up with the dandelions in your lawn if it is going to be used for romping and playing by the family. If they are just too much to put up with, then Confront applied according to label directions would be an example of an acceptable herbicide.
Q: I have a zillion dandelions and am wondering what is the best spray for them. I have
used 2,4-D, but it seems they enjoy the bath in that. Can you give me an idea
as to what to use? (Tappen, N.D., e-mail)
A: There are other products that can take care of dandelions, such as Trimec, for instance. This is a potent broadleaf weed herbicide that will take care
of the dandelions and others in your lawn. Fall application is best, as most of the seed that will be cast in the spring will be distributed all over, with new
seedlings coming up during the summer. They, along with their mother plants (the ones you see now in the spring), will be most vulnerable to the
herbicide at that time.
Back to Weed
Back to the Hortiscope Table of Contents