FALL LAWN CARE AND WEED CONTROL

By Diana Alfuth, Horticulture Educator UW-Extension

Is your lawn crawling with clover or dizzy with dandelions? The dry conditions the past two years have taken their toll on area lawns. Mid- to late September is the perfect time to get weeds under control and improve your lawn for next year. Existing perennial weeds, those that come back year after year, are best controlled by using an appropriate herbicide at this time of year.

While you may not see those dandelions blooming like they do in the spring, they are still very much active. With the onset of cooler weather and shorter day length, perennial plants have begun moving the sugars, starches and nutrients from the leaves down to the roots to store over winter. They also move herbicides extremely well at this time of year, which means the weed killer you spray on the leaves will more readily kill the root.

Using an herbicide such as 2,4-D or a mix of 2,4-D and dicamba as active ingredients is very effective on broadleaf (non-grassy) weeds. If you seeded a new lawn this fall, however, wait until next year to control the weeds. Lawns seeded less than 60 days earlier may have injury to the grass seedlings if you treat with herbicides.

As long as the weeds are still “active”—are green and have not yet gone dormant for winter--herbicides should be effective. Follow the instructions on the label for mixing and applying the herbicide.

Killing the existing weeds is the first step to a nice lawn next year, but if you have a major weed problem, you should try to determine why. A healthy, well- maintained lawn will have less weed problems.

Start with a soil test to determine if you have the appropriate pH and nutrient levels to support a healthy lawn. Soil tests can be done through the UW- Extension office, and fall is a good time to make necessary soil amendments.

If an area of the lawn is compacted, the grass will be stressed and you are more likely to have weeds such as white clover and plantain. If that’s the case, aeration is needed to allow more oxygen, water and nutrients to reach the grass roots. Plan on aerating in spring, and again early next fall if the soil is severely compacted.

Throughout the summer, be sure to raise your mower deck to at least 3”, and higher is even better. Taller grass will mean a better root system, so that the grass is more able to out-compete the weeds as well as sustain drought. It also helps prevent dandelion and other weed seeds from germinating in the first place.

Proper fertilization of your lawn also helps it out-compete the weeds. Fall is an important time to apply fertilizer to help the plants survive winter and get off to a good start in spring. Use early to mid-October as a rule of thumb for when to apply the last application of fertilizer for the year in our area, or whenever you think you are done mowing for the year. Apply approximately 1 pound of nitrogen per 1,000 square feet of lawn. “Winterizer” fertilizers also usually have extra potassium, which can help grass roots make it through the cold weather ahead. However, never apply fertilizer to a drought-stressed lawn. Wait until after a good rain or use supplemental irrigation prior to fertilizing.

During October, you could start gradually mowing your lawn a little shorter than you do over summer. This is optional, but might reduce snow mold and vole activity over winter if you’ve had those problems in the past.

If you have major recurring weed problems, it’s important to fix the underlying problems. For more information about lawn care, or any other horticulture topic, contact Diana Alfuth, Horticulture Educator, Pierce County UW-Extension office, at (715) 273-6781, or by e-mail.