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How to Divide Perennials

Jo.Baker
Published on August 25th 2019
43
A garden border filled with perennial flowers in front of a brick wall.
As our flowering perennials are slowing and starting to go over, now is an excellent time to think about moving some of those plants that didn't quite sit right to new locations.
Dividing perennials every third year helps to prevent them from outgrowing available space or overcrowd neighbouring plants. It can also improve their vigour by giving the replanted clumps a larger growing area. There's also the bonus of having more plants to either spread around the garden, give away or trade with friends.
A close up of the red and white flowers of Lamprocapnos spectabilis (Bleeding Heart)
Bleeding heart plants can be divided now while they are dormant. Take care with the brittle roots and discard any dried up sections.

What plants to divide in summer

Plants that flowered in spring are best divided between June and August, so we only have a week or two left to lift these.
Some of the plants you can divide in summer include:

Bearded Iris

Iris × germanica

A purple Iris sibirica flower on a plant

Siberian Iris

Iris sibirica

Bleeding Heart

Lamprocapnos spp.

Some pink flowers on a Pulmonaria officinalis plant

Lungwort

Pulmonaria officinalis

Phlox paniculata 'Top Shelf Series'

Phlox paniculata 'Top Shelf Series'

How to lift plants

  • Water the ground around the plant you want to divide to help reduce the stress the plant experiences.
  • Prepare the new site. Dig the hole and add any soil improvers or feeds the plant will benefit from. Reducing the time a plant is out of the ground increases its chance of survival.
  • Use a garden fork to gently dig around the plant's root ball and slowly tease the roots out of the ground. Facing the prongs away from the plant may be a bit awkward to do, but will reduce the likelihood of damaging roots.
  • Shake off any excess soil from the roots so they become visible. Remove any fleshy white roots intertwined with the plant's roots. These usually belong to perennial weeds, which you don't want to spread around the garden or pass onto friends.
A close up of a orange Hemerocallis (Daylily) flower above it's green leaves.
Daylilies have large fibrous roots that may need to be separated with a knife.

Dividing the plant

Once you've got the root ball out, it's time to divide the plant. Most books and television programmes will recommend placing two garden forks back to back in the centre of the clump and pulling the handles together to separate the roots. I wouldn't bother as it's hard and doesn't work very well. I use an old kitchen breadknife which works wonders. You could also use a very sharp spade.
Having sliced the clump into two or three parts, remove the older central bits as they will have reduced vigour. The clumps of younger roots, crowns or plantlets can be replanted or potted up straight away.
Water them well to help them settle into their new homes and then every ten days - during dry spells- until the autumn rains take over.
A garden Sedum being divided with a spade.
Hylotelephium's and sedums can be divided in Autumn but are best done in early spring when the new growth quickly reveals where the plant is.

What plants to divide in autumn

Plants that flowered before the end of June can be divided from September through to November, providing the ground is dry enough to work with. However, if we get a very wet autumn it might be worth waiting until spring to reduce the possibility of roots rotting off. Some plants to consider dividing soon include:

Plants to divide in spring

Those plants that are still flowering now will need to be divided in spring (March to May). This also suits slightly less hardy perennials.
Some of the plants you can divide in autumn include:

Plants not to divide

Plants that grow deep taproots rarely take to being moved or divided, but if they do, then they tend to be prolific seed producers. Collecting and sowing replacements will be the best course of action if you want to replace plants such as Verbascums, Eryngiums, Hollyhocks, Poppies or Acanthus.
A close up of the new red leaves with green veins of an Epimedium plant
Epimediums, like Hostas and Heuchera, have small fibrous roots which can be easily pulled apart into small clumps.
Before you begin dividing, my main recommendation is to spend some time planning what you'd like to move and where you'd like to move them.

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