How and When to Divide Perennials

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How and When to Divide Perennials

Tips to Know When It's Time to Divide Perennials

As the weather begins to cool for fall, it's time to start thinking about which garden plants would benefit from being divided. Labor Day is the traditional "deadline" for dividing Bearded Iris, but that's just a guidepost ÔÇö where you live, what the weather is doing, and most importantly, how your plants are behaving are the real signals to look for! 

First of all, if you're like us, you may be asking yourself, "Do I really have to divide any plants?" And while it's true that the Plant Division Police won't be patrolling your neighborhood, many perennials bloom and grow much better, and can even live longer, if divided every few years. Coreopsis is a prime example; if left alone, it can peter out after a few seasons, but if you take a moment every 2 to 3 years to pull it apart into smaller clumps and re-plant, it will thrive for a long, long time!

Here is a quick list of the perennials that benefit from a late summer to fall division:

  • Heuchera - Mark your calendar to divide this super-easy perennial every 3 years, removing the woody center of the plant and separating the healthy outer parts into several new plants.
  • Hardy Garden Phlox - Like Heuchera, this plant grows outward, creating a dead woody middle section every few years. If you divide Phlox faithfully every 3 years, not only will it live longer and bloom more fully, it will also be less susceptible to powdery mildew!
  • Hardy Geranium - Not every variety of hardy Geranium needs dividing, but considering what we pay for them, it's well worth it to break them apart every 2 to 3 years. They fall apart if just pulled gently ÔÇö no more than a moment's work for so much beautiful color!
  • Astilbe - Divide it every 2 to 3 years for best flowering and most vigorous growth.
  • Ajuga - This is a spreader, so it takes off like lightning after you divide it. Depending on how fast you need coverage, divide it every 2 to 3 years.
  • Hosta - This super-easy, super long-lived foliage plant can be divided any time of year, but fall works better than spring because it leafs out late, so it can hide from you until April or May ÔÇö by which time you're swamped with other garden chores! When you dig it up, you'll see that the rootball is divided up like a pie. Whack the divisions and you've got new plants!
  • Bearded Iris - If time is tight, divide your Iris first ÔÇö it needs to be divided and re-planted at least 6 weeks before the first frost, to give it time to root securely for winter. Look at the rhizome and cut off any parts that look dead or diseased. Then cut the rest cleanly into pieces, making sure to get at least 2 to 3 eyes in every piece.
  • Daylily - The busy gardener's best friend, this perennial is so easy that you can divide it without even digging it up, if you want ÔÇö just whack the base of the plant into 2 to 4 sections and leave it be! But you'll probably want to re-plant those new divisions elsewhere to increase your beautiful garden.... or possibly even share them with friends!