There is still plenty to do in the garden

You can do a lot in September that will help get your plants ready for colder weather and for next year.

If you have plants that prefer acidic soil, like rhododendrons and azaleas, now is a good time to add granular sulfur to the soil to create good conditions for them come spring. And if your blue hydrangeas have turned pink, a sulfur application might even return the flower color to blue. Just be sure to avoid contact with the sulfur by wearing latex gloves and keeping dust out of your eyes. Apply the sulfur to the soil and gently scratch it in. Sulfur works slowly, so you might need repeated applications from year to year.

Fall peony prep

Peonies are dependable, long-living, hardy perennials that are easy to grow, and September is a great time to plant them or divide and transplant the ones you have. After the large, showy blooms, their neat foliage generally stays green from spring until frost.

I’ve seen some peonies with powdery mildew this fall, so there can be exceptions to the clean foliage, but the plants with powdery mildew will recover next year.

They do best in full sun, and they can tolerate partial shade, but it might reduce flowering. If you’re going to divide and transplant, lift roots carefully and use a sharp tool to cut the large, fleshy roots into smaller pieces. Be careful not to make these pieces too small; each section should have at least three eyes. The eyes are reddish growing buds that emerge from the top of the roots, appearing in spring and fall. Set these divisions an inch or two below ground level to transplant.

Bring herbs indoors

It’s also time to start thinking about the indoor herb garden. Before frost hits, carefully lift and pot small herb plants or large perennials like rosemary or lemon verbena to bring inside. After lifting them from the ground, you may want to keep them outside for a few days, in partial shade with even moisture, since it’ll help them adjust to moving indoors. The shock from moving plants from outside to inside can cause some yellowing of leaves. Once inside, keep the herbs in a sunny window.

Be careful with herbicides in the fall

You can spray weeds late in the fall if hand weeding isn’t an option. Just keep in mind that herbicides are most effective when temperatures are consistently above 55 degrees Fahrenheit and weeds are actively growing. I recommend spot-spraying the weeds or hand pulling them to minimize the amount of herbicide you use.

Dandelions are easy to weed out of the lawn by using a soil knife to pry the roots out. Mitigating weeds now will save you some work when the next growing season starts.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.