Tom Karwin, on gardening · Jul 23, 2026
Designing with irises
Bearded irises want sun and a summer bake on the rhizome. Divide when bloom is over and the clump looks like a bird’s nest of old fans.
Bearded irises want sun and a summer bake on the rhizome. Divide when bloom is over and the clump looks like a bird’s nest of old fans.
The iris genus is large. For the garden it is enough to think in three horticultural groups: bearded, beardless, and crested. Tall bearded irises are the crowd — easy in open sun, endlessly hybridised, and sold as rhizomes in midsummer when the plants are resting from bloom.
Site first. Full sun and sharp drainage for most tall beardeds. Partial shade for some species. Small kinds for troughs and rock. A few for bog or pond margins. Putting a sun iris in a wet, dark corner is how gardeners decide they “cannot grow iris.”
Division is the design tool
A clump that flowered well two years ago and now is all leaf is asking to be split. Lift after bloom, in the local dormant window (often July–August in mild-winter climates). Cut or break the rhizome so each new plant has a healthy fan and roots. Replant shallow: the top of a bearded rhizome should see air and sun. Water in, then ease off once established — winter wet plus buried rhizomes is rot.
Society rhizome sales are how many coastal gardeners try new colours without catalogue prices. Label what you plant. In two years you will not remember which peach bit was which.
This week in the garden
If fans are packed and bloom was thin, put a division day on the calendar before autumn rains. If the bed still flowers well, leave it another year and spend the afternoon on something that actually needs you.
Enjoy your garden.
On Gardening columns for home growers. Independent notes on these topics — not affiliated with any newspaper. Timing depends on your climate.