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When and how do I divide irises?

September is a good time

Here’s the thing about writing a gardening column: There is so much great information to share and so little space to share it fully.

For that reason, I’m prone to offering lots of tips and suggestions, but not so much in the way of detailed guidance. It’s just hard to fit it all in! I always hope that readers who want to know more will seek out a knowledgeable source for assistance—Extension System experts, Master Gardeners, garden-wise friends and relatives, books, magazines and, yes, the Web. And, honestly, even if I had all the column inches in the world, I’d still encourage readers to track down experts who have loads more experience and knowledge than I will ever possess.

Still, my ever-creative and reader-oriented editors at Alabama Living offered an idea on how to better address the questions my tips and ideas may evoke. So here’s a stab at it, starting with a question my sister recently asked after reading a tip in my July column: So how do I divide irises?

Though the ideal time to divide irises it just after they bloom, in most parts of Alabama it’s fine to divide and replant them (and many other perennials) throughout the month of September, so it seemed an appropriate question to tackle this month.

Over time, the rhizomes (main roots) of irises produce lots of “baby” rhizomes that need to be removed and relocated so parents and children alike can thrive, thus the need to divide irises. To divide them, carefully lift the plant clump and its rhizomes/roots out of the ground with a garden shovel or fork, then gently separate individual rhizomes from the clump by snapping or cutting them apart. If you have more than one kind of iris in your yard, you may want to group them according to their color and/or cultivar as you do this.

Wash any excess soil off the rhizomes, soak them for 10 minutes in a 10:1 water:chlorine solution, then rinse them with fresh water and allow them to air dry in the shade for at least 30 minutes. From this freshly cleaned and dried collection, select the healthiest rhizomes for replanting or sharing and discard any that look diseased, shriveled or just plain puny. Try to replant them as soon as possible, preferably the same day.

As you replant the rhizomes, don’t bury them too deeply. Iris rhizomes need to be close to the soil’s surface and either partially exposed or only lightly covered with soil to reach their full blooming potential next year.

Another question my column recently elicited was about cover crops. Cover crops, unlike perennial ground covers used in the landscape, are annual crops that are used to hold and build soil between planting seasons in vegetable gardens.

As the summer gardening season comes to an end, you can replant the area with cool-season vegetables (cabbage, collards, lettuces, garlic and onions, for example).

But if you’re planning to leave the space dormant this winter, consider planting it with crimson clover, rye, soybeans, hairy vetch, oats and other legume or cereal crops. These crops help hold the soil in place, build soil quality and, depending on the cover crop you choose, can add nitrogen to the soil, suppress weeds, help control some insect and disease pests and attract pollinators.

Cover crops will protect and enhance your soil all winter and, next year, can be used as “green manure” by mowing the cover crop in late winter or early spring, letting it dry for a week or two, then working the crop residue into the soil as you prepare the garden for the coming vegetable season.

More information on what kinds of cover crops to use and how to use them in vegetable gardens can be found through your local Alabama Cooperative Extension System office or in the Extension publications Cover Crops for Alabama (available here) or The Alabama Vegetable Gardener (available here).

And if you have gardening questions, send them on. If I don’t know the answer I will try to find someone who does, and your question may well be fodder for a future column!

Katie Jackson is a freelance writer and editor based in Opelika, Alabama. Contact her at

September Gardening Tips

  • Make notes about what did and didn’t work in this year’s garden for use as you plan next year’s garden.
  • Clean dead plants and debris from garden beds and the landscape.
  • Add lawn and garden debris to the compost, along with any organic (non-meat) kitchen waste.
  • Test your soil so you’ll know what amendments to add this fall and winter.
  • Plant fall and winter vegetables and root crops, such as cabbage, collards, celery, garlic and onions.
  • Continue to mow and irrigate lawn as needed.
  • Fertilize azaleas and camellias.
  • Plant winter grass seeds on bare areas.
  • Plant perennials and biennials and spring-flowering bulbs.
  • Divide perennials and thin or transplant irises and daylilies.
  • Clean bird feeders and birdbaths and keep them filled throughout the fall for resident and migratory birds.