Early fall is prime time to tackle lawn improvement

The garden gets tired by September. As the perennials fade, I feel my interest in the garden flagging, too.

But we Minnesotans need to rally our energy, especially where lawns are concerned. Fall is the best time to tackle many lawn chores, including killing weeds and fertilizing.

Dandelions and creeping Charlie are growing like crazy in the spring, and unless you get to them when the plants are young, it's harder to kill them when they're growing so quickly. In the fall, perennial weed growth slows, and the plants pull nutrients into their roots in preparation for winter. They're sitting ducks for targeted weedkillers.

Dandelions usually succumb to a single application of weedkiller. Creeping Charlie is a tougher customer. Often two applications of a herbicide containing triclopyr or another chemical labeled for use on the plant are needed. Make sure creeping Charlie, ground ivy or the plant's Latin name, glechoma hederacea, is listed on the herbicide label as a targeted plant. The first application can be applied in early September, and if the plants are still thriving two or three weeks later, apply again.

Never use more chemicals than the label indicates. People sometimes think they can increase the effectiveness of weedkillers by applying more than they should, but doing so is not only dangerous but may even negate the herbicide's effect.

For a while, a suggested alternative treatment for creeping Charlie was a homemade formula using 20-Mule Team Borax. While the recipe generated some excitement in the 1990s as an alternative to conventional weedkillers, it is not an "organic" solution and in fact will permanently damage soil if used more than once. The boron in the laundry solution stays in the soil and will kill grass. Because of this, university extension services that once promoted this mix as an alternative no longer do so.

Remember that if you want to kill weeds only, buy something appropriate for the job. Spot treatment of weeds with Roundup will kill grass as well, while herbicides that are labeled specifically for weeds won't hurt the grass.

Seeds of improvement

If you have a problem lawn, fall is a great time to tackle that project, too. Cooler weather is great for sprouting grass seed, and there are fewer weed seeds to contend with than in the spring. The weeks leading up to mid-September are an ideal time to sow grass seed.

Many weeds thrive in compacted lawns where kids, dogs or general traffic have pressed down the soil, making it difficult for grass to grow well. Plantain, prostrate knotweed and spotted spurge are common in lawns with hard-packed soil.

Aerating the lawn will break up compaction, making it easier for grass roots to penetrate the soil and for nutrients and oxygen to reach those roots. You can rent an aerating machine or hire a professional to run an aerator over the grass. The machine pulls soil plugs that look like little cigars out of the lawn.

To make a difference, the machine should be run over the lawn several times until it looks really awful. The lawn will bounce back within a couple of weeks, and the soil plugs will disappear into the grass. Aeration should be done after a rain or good watering so the machine's prongs can easily penetrate the ground.

Here's a guide to lawn renovation from the University of Minnesota Extension Service:

extension.umn.edu/garden/turfgrass/repair/lawn-renovation/index.html

Time to fertilize

Lastly, fall is the most important time to fertilize lawns. If you fertilize just once a year, do so around Labor Day. According to experts with the U extension service, fall fertilization's benefits carry forward into spring. Spring fertilizing can actually stress lawns, those experts say, by encouraging green growth just as summer dryness hits. Fall fertilization stimulates green growth in the spring but also tends to reduce summer disease.

Fussing over lawns has fallen out of fashion in a time when many homeowners are wary of chemical use and want a more carefree approach to caring for their grass. But steps including aeration, fall fertilization and fall seeding of bald spots are among the best ways to fight weeds.

A healthy lawn beats back weed invasions. And just like rain gardens, lawns are one of the best ways to catch and absorb rainwater that otherwise would rush into streets and storm sewers.

Meanwhile, if you have time and the inclination to work in the garden (after working on your lawn), there's still lots to do. Top tomatoes (cutting off stems that are taller than the cage), divide peonies and daylilies, and get rid of perennials that have lost their appeal.

Mary Jane Smetanka is a Master Gardener and Minneapolis freelance writer.