The Aster (Aster dumosus) in an autumn garden. (Photo: Shutterstock).
Deryn Davidson, Colorado State University Extension – Boulder County

It’s hard to believe but September is upon us. Nighttime temperatures are dropping, leaves are slowly beginning to change and if you’re lucky, soon the smell of roasting chilies will hang in the air. While noticing these seasonal changes starting to take place, I realized that all summer long, I’ve been waiting for summer to start. There weren’t the usual outdoor summer concerts, early camping trips were canceled due to the pandemic and life has been anything but normal. I also had a very grounding realization that although I’ve felt like I am in a holding pattern, the natural world has marched on. Life as we knew it changed abruptly, but I take great comfort in knowing that flowers kept blooming and the bounty of vegetable gardens and farms filled our plates.

Now that we’re slowly making our way into fall, what are some of the garden tasks to be done? We still have several weeks of gardening season left, but now is a good time to assess how things did this year, make notes and plan for next year.

In the vegetable garden: Did you try some new vegetable varieties? Were they a smashing success or one-and-done? Keeping notes will help your planning efforts for next year. As plants start to finish up and there is nothing more to harvest, you can remove them from the garden and get them into the compost pile. That is, if they are disease free. Plants that you think might have any fungal or bacterial malady are best put in the trash, so they don’t live-on in your compost pile. Now is also a good time to make sure you have access to some sort of frost cloth or light bed sheet to cover those tender veggies, herbs or annuals that could get nipped by an early frost.

Perennials: How did your ornamental garden do? Did you lose anything? Is there overcrowding? September and October are great months to divide existing, and plant new perennials. There is still enough time for the roots to establish before winter hits and the plants go dormant. If you have iris or daylilies that aren’t blooming as vigorously as they once did, dividing them in later summer will refresh them for next spring. If you have perennials that have outgrown their space and look crowded, dividing and transplanting them on a cool day will set them up for better growth and performance in the years to come. If you need to replace any plants or have areas that are ready for something new, it’s a great time to visit garden centers and nurseries and find those new additions. Make sure you keep all of these well-watered through the end of the season and apply a 3 to 4” layer of mulch to hold the water in and protect them over the winter.

Plant bulbs: If you don’t have any bulbs in your garden, I highly recommend trying some. Planted in the fall, they will bring bright pops of color to your garden in early spring. If you already have bulbs, why not try something new? Even though it’s still a little too early to plant them, now is the time to buy them. Selections get picked over quickly, so you want to make sure you have time to get what you want. There is a huge variety and they come in all colors and heights for great garden interest. The best time to plant bulbs is mid-September to late October, again so they have time to establish roots before the soil freezes.

For more information on all of these topics, check out planttalk.org and use the search bar to find what you’re looking for. Happy fall gardening!

By Deryn Davidson. Deryn is an Extension Agent – Horticulture at Colorado State University Extension Boulder County. For more information contact CSU Extension at the Boulder County Fairgrounds, 9595 Nelson Road, Box B, Longmont, 303.678.6386, e-mail ddavidson@bouldercounty.org or visit boulder.extension.colostate.edu.