GTI Lawn & Garden Letter

Entertaining advice for home gardeners with a focus on lawn and garden care and the outdoor gardening lifestyle. Suitable primarily for people living in northeastern North America and similar temperate climates in other parts of the world.

Thursday, May 15, 2008

Dealing with Dandelions

Once again we enter the season when dandelions reveal their golden flowers across lawns, fields, ditches and parks. I could probably write an entire post about the pluses (pretty flowers, salad greens, wine, and the fact you can make a cool necklace by looping the flower stalks) and the minuses (ugly flowers, crowds out the grass, makes a lousy playing surface, seed blows everywhere and gets into my perennial border) of this controversial plant/weed. However, since this is a place where gardeners come to look for advice about lawn care, I will restrict my comments to managing dandelions in your lawn, or should I say out of your lawn.

Ontario residents are probably aware that the provincial government is introducing legislation to eliminate the cosmetic, or non-essential, use of pesticides on lawns and gardens including those used to control dandelions and other broadleaved weeds. If you are interested in this legislation, check out this link where you can read the draft legislation and provide your own comments if you are so inclined. The bottom line is that if you are currently using a weed and feed fertilizer, a three way herbicide like Killex or having a professional service treat your lawn to control dandelions and other broadleaved weeds, this may be the last year you can use these products. Start planning now to refine and change your management practices to reduce weed populations by other means or alter your expectations and learn how to make dandelion wine.

As a starting point, when dandelions are flowering is not the best time to control them using traditional herbicides. At this time of year, they are putting all of their efforts into producing seed so treatment may affect the leaves but the roots will likely survive and regrow. The treatment will not affect seed production. Fall treatment is most effective at controlling dandelions as they are directing their energy to the roots for winter survival.

In the spring, your best option is to dig out your dandelions. You want to remove as much root as possible so hand pulling is not really an option. A number of tools are available for this job. I have experimented with a few of the available models and have yet to find one that is 100% effective at getting all of the root and preventing regrowth. My current strategy is to use a model that removes the weed, about the top 6-8 cm of root and a small cone of soil. I carry a bucket with some good topsoil mixed with grass seed and toss a handful in each of the little holes to prevent other weeds from germinating in the void. If you have a large lawn and currently have a good crop of dandelions, consider treating your lawn one last time this fall then plan to improve your cultural practices and start manual removal of weeds next year.

There are some options for weed control that will still be available as well as some new options on the horizon. Corn gluten meal has been around for a few years. Normally used as a pet food ingredient, it was found to also prevent seed germination. It has no impact on established weeds but will prevent new weeds from germinating. Unfortunately, it will also prevent grass seed from germinating so you should avoid using it if you are overseeding your lawn to increase turf density. It is particularly effective in a program to control crabgrass, an annual grass that is a weed in lawns and is starting to germinate right now. For more information about this product, including how and when to apply, follow this link.

Within the next year or two, watch for a new product called Sarritor. Expected to be commercially available in 2009 or 2010, this is a true "biological control agent" in that it is a living organism, in this case a fungus, that selectively attacks dandelions and may also have some activity against other broadleaved weeds. Watch for further information on this product or check out their website.

Once you have eradicated undesirable weeds from your lawn, plan a good maintenance program to keep your lawn thick and healthy. A long term demonstration project looking at lawn care alternatives conducted at the Guelph Turfgrass Institute over the last few years showed that fertility was one of the major factors in reducing weed infestation on lawns. The most important aspect from both an agronomic and an environmental perspective is to apply the correct amount of fertilizer at the appropriate time of year. For a moderately managed lawn, you should fertilize twice per year - sometime in the next four weeks (late spring) and in late summer/early fall. I follow a three times a year application schedule on my lawn that adds a late fall application that I think is important for winter survival and early but controlled spring green-up and growth. It is critical to apply the correct amount - go back and see my May, 2006 posting (link at the right side of this page) for information on how to accurately calculate your lawn's fertilizer needs as well as a discussion on organic versus inorganic fertilizers. A soil test taken in the fall every 2-3 years can point out any odd nutrient deficiencies but nitrogen is not measured by soil tests and is the most critical nutrient for grass.

Combined with good mowing practices (a sharp blade, mow high and return the clippings to the lawn), periodic aerating to manage thatch and overseeding as needed to increase turf density, it is not that difficult to have a lawn with no chemical intervention needed. Insect problems are going to be the greatest challenge of managing pesticide free landscapes. Keeping the lawn thick and healthy will help as will quickly overseeding any damaged areas. Hopefully the elimination of pesticide use will help stimulate investment in research to develop effective alternatives so we can still enjoy the environmental, recreational and aesthetic value of our lawns.

We are working on a new website for the Guelph Turfgrass Institute & Environmental Research Centre, and our intention is to eventually move this blog there as well as develop an extensive list of frequently asked questions about lawn care and other helpful resources for home gardeners. I'll keep you posted on new developments and welcome your comments, suggestions and questions. In the meantime, enjoy your lawn and garden and have a great Victoria Day weekend.

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