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Top 10 Tips on Easily Dividing your Perennials

February 16, 2014

Accidentally made this cumin plant look cool. It was long and stringy and I hacked it about a month ago, and this happened...

1) Divide when they are pretty, not after they have outgrown their space.

It’s like when kids outgrow their clothes, you won’t let them wear them for another season… you go buy then a size up!  So when the plant looks it’s greatest, and you find yourself standing in front of it admiring it that you make a note in your gardening journal to divide it at the end of it’s growing season.

2) Divide in mild weather.

You wouldn’t put a new plant in the ground in the heat of summer or try to break into icy dirt to plant anything, so this is an easy one to remember.  Divide at the end of a growing season AND in mild weather for a freshly divided set of plants to get their best start.

3) Dig at the drip line.

The drip line is the imaginary circle around a plant where you would imagine rain rolling off the leaves and landing on the ground spherically around the plant.  Dig THERE!  Then you will be getting the bulk of the root system.  One of the things that are most frustrating to a detail person like me is to know you have to dig up all the roots when you can’t visibly see them until you’ve already stuck a sharp shovel into the ground and potentially severed your favorite plant!  Digging at the drip line pretty much guarantees that you’ll avoid hurting any important parts of your plants.

4) Remember 50/50…

Keep the divisions that aren’t going right back into the earth around 50 degrees F and 50% humidity.  A cool garage is a good storage place.  And you could wrap the root in wet newspaper to buy it some time.  Do try to plan to divide the same day that you replant though.  That’s the best way to ensure good plant health.

5) Add New Soil

I always have three fresh bags of good garden soil on hand at all times in the growing season.  If I know I’m almost out I go grab some more.  When you pull a plant from the ground and divide it you can’t put half of a plant back with half the soil or it will lack  the soil luster that it had that made it gorgeous that last season.  Remember soil is a huge part of the equation that makes a beautiful garden.  I usually divide, fill some of the hold with new soil, put the half plant back in and mound new soil over the top until it’s ever so slightly above ground level.  Not a hill though because the purpose of the height here is simply to ensure that after the first rain it settles to a level height.

6) Replant only 20-25% pieces.

Unless you want to be dividing every single year, this rule is paramount!  So, to the UNgardener… you could imagine this is a rule like no other!  If I divide a plant into two pieces, then replant them into two holes in my yard I am pretty much guaranteeing myself to have to dig up and divide two plants next year.  Then by the laws of multiplication, I will have twice the number of plants the following year (4, then 8, then 16, then 32…) if I again divide in half and replant… By nature, perennials are vigorous growers.  They want to perform for you like good pets.  For that reason we should be grateful.  But, when it comes to reducing the work load, remember to only replant at around 20% the size of the original plant.  This will allow us to really pick over the roots and select the healthiest looking sections for replanting.

7) Replant only the healthiest pieces.

That last point having been said, it’s seems quite obvious that you would only replant the healthiest looking root pieces.  If I only need 20% of my root to make a new healthy plant I can afford to weed some of the roots out for trash.  Once I had about 10 hostas to divide, and they were almost 3 feet around at the time and growing into my walk way.  I broke those 10 plants into 40… surely I didn’t need 40 new plants.  I was able to weed through them, trash some, replant some, and fill two of my friends’ yards with them.  Aren’t perennials good little pets?

8) Make the hole as wide and tall as the roots when spread out.

In the next growing season you can imagine that the plant, if healthy, will be as wide as it’s roots when spread out in the hole.  Therefore, you want the plant to be able to concentrate on growth of the plant, not first to have to concentrate on spreading out its roots.  All plants will first focus on growth underground before being able to concentrate on beautiful stems and flowers above ground.

9) Divide according to its root type.

When you dig up a perennial, you will see that it fits into one of five basic root types

  • Roots that form clumps or offsets – To divide a plant whose roots form offsets (small plants growing at the base of
    a larger one), snap the connection between any of the sections to obtain a piece with ample roots and three or more growing points.  (Examples:  Asters, Hostas, Coneflowers, and Tickseeds)
  • Surface roots – Some perennials have roots that run on or just below the surface of the soil.  They form new crowns and roots when they reach open spaces or make contact with the soil. If you cut between any of the stems as you would cut a piece of sod
    from a lawn, you will have a division with its own stems and roots.  (Examples:  Bee Balms, Black-eyed Susan, Creeping Sedums, and Creeping Speedwells)
  • Underground running roots – Underground running roots can develop suckers as they grow beyond the shade of
    the mother clump. These suckers can be cut away from the main plant, or you can dig up the main plant and cut away any piece with an eye or sucker already forming.  (Examples:  Hardy Geraniums, Japanese Anemones, Ostrich Fern, and Plume Poppies)
  • Taproots – Plants that have taproots can be divided by using a sharp knife to slice down the length of the root. Every piece that has at least one eye, some of the taproot, and a few side roots is a viable division. (Examples:  Balloon Flowers, Butterfly Weeds, Cushion Spurges, and Oriental Poppies)
  • Woody roots – Woody perennials often form roots when stems rest on the ground or are buried by gradually accumulating mulch. Make a new plant by simply cutting between the rooted stem and the mother plant. (Examples:  Candytufts, Euonymus, Lavenders, and Sages)

10) Wear Gloves.

Always wear protective gardening gloves when dividing plants.  This is a good idea for a couple of reasons.  First, it’s just more comfortable to not worry about hurting yourself.  Second, on some plants the sap could irritate your skin.  And third, because a better grip could allow you to do the job quicker, and quicker is the name of the game for the UNgardener!


The UNgardener


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