Lifting and dividing irises

The Irises at Sissinghurst

• Along with roses and peonies, irises are the other key plant for us at Sissinghurst.
• Bearded irises have rhizomes and a fuzzy 'beard' running down the centre of the three petals that hang down from the flower (falls).
• There are tens of thousands of bearded iris cultivars, classified by height: small, intermediate, tall.
• We traditionally grow the tall varieties because they have more presence in the border and are from the period, so they feel cohesive in the garden.

Bearded Iris Care

• The top-heavy flower stems can flop, so tie the stem to a short stake as it grows.
• Snap off faded flowers from the stem to leave just the fresh ones.
• Straight after flowering, between mid-June and mid-July, lift and divide those that haven't flowered well. Few flower spikes for the size of the group indicate that it's time. This usually happens after 4-5 years – the rhizomes run out of space and energy.
• We do this in the short window when they've finished flowering but before they start growing new roots. If done then, they will very soon naturally start growing new roots.
• Lifting and dividing takes some time, so we do a few clumps each year.
• If you notice poor flowering in the interim and don't have time to lift, you can cut unproductive pieces off the rhizomes in situ.

How to Lift and Divide Irises

1. Remove the tie and stake.
2. Remove the faded flower stem. Secateurs can leave a stub, so snap it off at the base instead for a clean break with no stub left. Look for the direction the rhizome is going and push the flower spike from the base in the direction of the rhizome.
3. With a border fork, hand fork or trowel, lever underneath the rhizomes to lift the clump.
4. Put the clump on a hessian sheet. Tease apart the rhizomes and look for unproductive and productive pieces. Keep plump, firm sections with buds and leaves, and cut off and discard the old, unproductive end with no shoots or roots.
5. To conserve moisture, cut the leaves down to an arrow shape.
6. Prepare the soil by digging in some homemade compost. Though irises like it stony, gritty and sunny, the new roots do need nutrients.
7. Replant the rhizomes at around 6-8in spacing. Face them towards the south so they're not shaded by the leaves. Ensure the roots are under the soil but the rhizome is on the soil surface. Scoop a hole, thread the roots in and cover them over with soil. Firm around the roots while holding the rhizome at the right height to stay exposed.
8. Spread a thin layer of coarse grit around the rhizomes, without covering them, to stop water sitting around the rhizomes.
9. If you have acidic soil, scatter half a handful of lime around the rhizomes.
10. Pin the rhizomes in place with a U-shaped piece of metal wire to prevent windrock as the regrowing leaves catch the wind.

Pairing Annuals with Bearded Irises

Irises are fleeting, so you can interplant them with delicate annuals that flower between the irises without shading the rhizome.

Delicate annuals I plant among irises:

• Verbascum phoeniceum (purple mullein and also the white form)
• Nigella (love-in-a-mist)
• Galactites tomentosus (purple milk thistle)
• Viola cornuta Penny™ White (pansy Penny™ White) – a perennial, but often used as bedding.

The Value of Bearded Irises in the Garden

• From lifting and dividing, you'll have spares that you can spread around the garden.
• Irises are quite expensive, but from buying one pot, you'll quickly have enough rhizomes to make several groups.
• Irises may be fleeting but are more special for it and provide a moment of luxury among the stalwarts of other perennials like geraniums, pansies and salvias.
• Little highlights like this are important in a planting scheme.

They evoke such a feeling of both the exotic and the traditional English cottage garden. They're ephemeral, but actually they're more special for that, and I look forward to the moment they flower

Plant Directory

Geranium species and cultivars

Hardy geraniums, cranesbills

Hardy herbaceous perennials

Geraniaceae

Iris germanica species and cultivars

Bearded irises

Hardy herbaceous perennials from rhizomes

Iridaceae

Nigella species and cultivars

Love-in-a-mist

Hardy annuals

Ranunculaceae

Verbascum phoeniceum

Purple mullein

Hardy evergreen biennial or short-lived perennial

Scrophulariaceae

Viola cornuta Penny™ White

Pansy Penny™ White

Hardy evergreen perennial

Violaceae

Viola × wittrockiana cultivars

Pansies

Hardy evergreen short-lived perennials

Violaceae

Sourcebook

• Melcourt horticultural coarse grit 20kg – use the 'where to buy' feature, selecting horticultural coarse grit from the dropdown list, to find a stockist near you. It's worth phoning your local garden centre to double-check whether they stock it, as it's possible they may not be listed above. If there are no stockists near you, you can order online here for delivery at a fee.
• Check your local garden centre for horticultural or garden lime (calcium carbonate).