Wednesday, April 13, 2011

Divide & Conquer

Who wouldn't want more of these?
'Rozanne geranium' is a 5 star perennial which can
be divided after several years growth. That makes
more for your garden - or for your friends.


It’s that time of year when we see that the garden is coming back to life and notice that our black eyed Susan’s (Rudbeckia) are hell bent on swallowing the nearby Rhododendrons or the “nice big hosta” is a monster this year and you have to pole vault over the top of it to walk along the path. Sound familiar? So which perennials can you divide at this time of year, how do you know they need to be split (apart from the aforementioned pole vaulting through the garden) and how do you go about it?

Basically you can divide any perennial which isn’t about to flower. Even then you can split them if you have to; you’ll just lose the flowers this year as the plant goes into recovery mode from your less than timely surgery.
This Siberian iris is ready to be divided; notice how it has
died in the center. A good sharp whack with a spade
will sort it out.




You can tell when a perennial needs ‘the operation’ when it has a bald patch in the middle (Siberian iris and ‘Autumn joy’ sedum are notorious for this), they flower less than usual, or are just so congested that you can hear their screams for help.

There are several methods to resuscitate and revive such sad plants which I select according to plant type or personal energy.


1. The ‘Stomp & Whack’ method. This is perfect for those of you with little patience, little time and hefty feet. For the seriously lazy gardener just leave the patient where it is, aim a sharp spade overhead and stamp down hard like a guillotine a few times. Assuming you weren’t wearing flip flops your feet will be fine but the plant will be dissected into chunks. Sure there’ll be a few lost leaves and bits of roots here and there but there will be enough good pieces to lift and replant elsewhere. This works really well for hostas and big grasses, and you can often yield 4-6 good sized pieces. However in defense of the humble hosta I should probably tell you that it never needs dividing for its own sake. It is happy to just keep growing bigger every year, so it only needs this brutality if you need to beat something up or the hosta has got too big for its allotted space.

Daylilies need dividing when they no longer bloom well.

2. The Playtex effect. (a.k.a. ‘lift and separate’). Basically the same as above but a little more genteel. For one thing the entire clump is lifted out using a large digging fork. This is a better way to go than a digging spade which will sever the roots whereas the tines of a fork which will go between them. Once lifted the clump is set on a hard surface such as a stone path or patio or an open section of soil. Then use two forks back to back to pry the root ball apart into sections. This allows for separation of plantlets along natural divisions so is ideal for dividing daylilies. Discard any weaker central sections and replant the other pieces.
It is easy to see the individual plantlets within a daylily clump

3. Surgical precision. It’s quite fascinating when you look at how plants grow. Some just keep growing out from the middle but others like black mondo grass produce little babies on shoots a few inches from the parent, rather like the indoor ‘spider plant’ (known as the airplane plant in the USA). These can be emancipated using pruners or a sharp knife as soon as the babies have some roots of their own. When buying this grass I look for the pot with the most ‘heads’ (growth points) in it, knowing that I can divide my ridiculously expensive treasure into lots of plants and so end up with a bargain (which justifies my spending money on another plant of course).

4. Cookie cutters. Want to divide groundcovers such as creeping thyme, Corsican mint of blue star creeper? These all have a fine network of threadlike roots which form a mat under the carpet of foliage. Use a bulb planter to push down, twist and lift up a plug which can be replanted in a new area. Just fill in the hole with a little fresh soil and the ‘wound’ will quickly be concealed.
Heuchera 'Peach flambe' responds well to
decapitation! I managed to propagate
a nice carpet of this variety, all from
one plant.


5. The “Off with its head” approach. Some plants like Heuchera grow up from one central crown. After a few years most varieties look rather like colorful giraffes with their necks sticking up much farther than is attractive. You can see tufts of fresh new growth at the top of the neck but the rest of the plant does not say ‘designer’. Since many of the newer varieties seem to grow from one central crown you can’t use any of the above methods to propagate Heucheras. However you can snap or snip off the tufty top and a few inches of ‘neck’. Pull a few leaves off the neck (this is where the new roots will emerge from) and plunk it into a new patch of soil, buried to just beneath its head. I’ve had about 80% success rate with this and since Heucheras can cost as much as $20 for a choice variety its’ worth a try.

A few basics
  • Don’t do this on a very sunny day; overcast, cooler weather is better.
  • Division in easiest before the plant is fully leafed out
  • When replanting sections there is no need to fertilizer but a handful of compost mixed in with the soil as you tuck them in isn’t a bad idea.
  • Keep well watered; these little babies will be stressed enough without being thirsty too.

Popular perennials and the best methods for division
Old fashioned bellfower (Campanula 
persicifolia) is a classic cottage garden
perennial. It self sows and spreads easily
but should you want to give some away
just show it that spade!


Yarrow (Achillea); 1 or 2
Bugleweed (Ajuga); 2 or 3
Lady’s mantle (Alchemilla mollis); 1
Japanese anemones; 2
Goats beard (Aruncus); 1 when small. Backhoe when not…
Michaelmas daisies (Aster); 1 or 2
Elephant ears* (Bergenia); 2 or 3
Bellflowers (Campanula); 1
Tickseed (Coreopsis); 1 or 2
Coneflowers (Echinacea); 1 or 2
Bishop’s hat (Epimedium); 1 or 2
Bearded iris; 3
Catmint (Nepeta); 1 or 2
Peony; 2 or 3. Yes they can be divided…
Lungwort* (Pulmonaria); 1,2 or 3
Black eyed Susan (Rudbeckia); 1 or 2

* wait until they have finished blooming in another couple of weeks.

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