Public Service Announcement: Fall is the best time of year to feed your lawn.
When it comes to fall feedings, think of your options as a “choose your own adventure” situation.
Option 1: The “Regular” Step 4: 20-0-8 w/ Q3 (The Weed-and-Feed)
If you have had any issues with weeds in your lawn this season, now is the best time to prepare to apply Step 4 (11,000 square feet/bag). The ideal timing for the application of this product in Iowa is any time between the end of September and the end of October. That said, this product can be used any time of year when the weeds are actively growing. This means some folks who are playing “major catch-up” on a property might use it in June and then again in the fall. This can be an effective strategy for lawns that have been long-neglected or are simply overrun for one reason or another.
Note: This question is really asking, “Did you EVER have weed problems in your lawn this year? How about dandelions this spring?” The most effective time to stop weeds for next spring is this fall.
Purslane is a common broadleaf weed in compacted soils. If you have lots of purslane in your lawn, schedule extra aerations in the coming years to help prevent this weed naturally.
Why Fall??
It’s science. In the fall, plants put lots and lots of effort into storing energy to help them get through the winter. When someone applies an herbicide in the fall, the plant is biologically primed to take the weed killer into the depth of the plant, ensuring a greater likelihood the entire plant will die efficiently (with as little application of the product as possible).
Can you use a weed and feed at other times of the year? Yes. But they will be less effective than they will be in the fall.
When treating weeds, it is helpful to know what weeds you are trying to target. There are many species of broadleaf weeds that can be found in home lawns and other turfgrass sites. These species vary widely in their appearance, competitiveness, and level of difficulty to control.
They can also have various life cycles including annuals, biennials, and perennials. Understanding plant identification, growth habit, and lifecycle are all important in deciding how best to control them, or whether to bother treating them at all.
What is a broadleaf weed?
Broadleaf weeds are dicotyledonous plants (dicots) with leaves that emerge in pairs after germination. Their appearance often catches our attention for many reasons. Unlike grasses, broadleaf weeds often have showy, colorful flowers that can emerge from the canopy several days after mowing. They have various leaf shapes, arrangements, and margins, and can have prickly leaves or fruits that stick to clothes and pets. Furthermore, their spreading growth habit can interfere with turfgrass health and performance.
Do I have to use chemicals to stop them?
Iowa State mowing heights and weed pressure study - Photo credit: Dr. Quincy Law
Not necessarily. It is important to note our cultural practices on the lawn can also have a big impact on weed pressure, both positively and negatively.
For example, consider this image from a mowing height study done by Dr. Quincy Law of Iowa State University. These plots were fed identically (without crabgrass preventer). You can clearly see that the lower the mowing height of the plot, the more pressure occurs from crabgrass.
Routine mowing will prevent many broadleaf weeds from flowering, which helps reduce or prevent the spread of weed seeds.
Iowa State feeding practice and weed pressure study - Photo credit: Dr. Quincy Law
Another cultural practice that will impact weed pressure is your feeding program. This second photo from Iowa State does a good job illustrating how feeding practices will influence weed activity in the lawn as well. It is important to point out in this case that the Nitrogen (N) being used for feeding these study plots is not killing the dandelion weeds. Rather, the thicker stands of turn (a result of the stronger feeding program) are doing a better job of naturally crowding out competition.
Some broadleaf weed species can be removed by hand. They often have large leaves and fleshy tap roots that make them easy to pull up with a quick grasp, hand tool, or small shovel. People are often surprised how quickly a few minutes of hand-pulling here and there can make a large impact on removal. That said, be very careful to ID the weed prior to pulling, as some weeds, like Creeping Charlie will spread more aggressively as a result of pulling.
I’m mowing and feeding well, but I still have broad weeds!
It’s ok. Let’s talk chemical control options.
Prostrate weeds that grow close to the ground will not be impacted by mowing, which is one reason they are sometimes harder to control. Many broadleaf herbicides are combination products of two, three, or even four herbicides designed to expand the spectrum of weeds controlled.
It is not uncommon for a broadleaf herbicide to list hundreds of weed species on the label. When using these products, do not mow three to four days prior to spraying to ensure there is plenty of leaf tissue available to absorb the herbicide droplets as they land. Additionally, try not to mow two to three days after application so the herbicides have time to translocate into stems, rhizomes, tubers, etc.
Pro Tip: This is why Step 4 is the “weird” step of our four-step program, as it is applied when the grass is dewy and/or wet in the morning, and you do NOT want rain for at least 24 hours afterward.
This is a cute, but ineffective method of killing Creeping Charlie.
Some broadleaf herbicides will result in visible injury within hours of application, but most take more time to fully kill the weed. For perennial broadleaf weeds, such as Creeping Charlie, a second application may be necessary two to four weeks later.
Although weeds may look dead after the first application, there is a potential re-growth period from underground storage organs whereby new leaves are produced.
Other general guidelines include not spraying when the weed or lawn is under any type of stress from heat, drought, or cold and being cautious on warm-season turfgrasses during spring green-up. As always, be sure to follow the product label’s directions and use these products judiciously.
A note about Creeping Charlie: Creeping Charlie is a weed in a league of its own. Because it is so difficult to kill, we recommend getting a spray specific to Creeping Charlie (also known as Wild Violets) and following the label to kill this tenacious plant. It is NOT possible to kill Creeping Charlie by pulling it (or dethatching the area).
Bear in mind Creeping Charlie tends to thrive in shady areas where there is too little light for grasses to be thick and lush. Consider having surrounding trees limbed by a professional arborist to introduce more light into the area to promote more competition from the surrounding grasses.
What about grassy weeds?
Those, my friend, are a whole other ball of wax. Read more about controlling them here.
Option #2: Thickening, Strengthening, and “Winterizing” (without weed control)
Is your lawn mostly weed-free but could be thicker and healthier? Was the drought or derecho hard on parts of the lawn?
Feed it. Iowa is literally the grassland of the nation; you will be amazed how much your lawn can do in terms of self-repair if you provide the food it needs to get the job done. Remember, you can repeat feedings with 13-13-13 as often as every three weeks until you feel the lawn is fully healed and ready for winter. For people with heavy clay lawns or dogs, now is also a great time to apply gypsum to help repair dog urine damage.
Bonus Question: Did your lawn underperform in general this year? Mark your calendar to bring us a soil sample first thing in the spring so we can design a more effective feeding program for your lawn for next year.
Pro-Tip: Fall is the best time for Aeration
The ideal aeration is a core aeration that pulls 3” plugs.
This fall, we received several inquiries regarding possible diseases in the high heat and humidity of August and early September, as well as thatch build-up in yards. These issues were almost always seen in compacted, poorly drained soils.
The easiest and most efficient way to prevent the possibility of diseases in your lawn from year to year, in addition to promoting the healthy breakdown of thatch, is core aeration.