One of the great joys of growing irises is that they reproduce new plants every year which will give you loads of new plants for your own garden as well as presents for friends and family.
The best time to divide your iris plants is about 6-8 weeks after flowering.
You’ll find after 3-4 years the single iris you planted has turned into a ring of new plants joined to the old central rhizome, or ‘mother’.
Lift the whole congested clump.
Dig down deep to get as much root as possible and try to avoid damaging any newly formed flower buds.
Cut the new, outer rhizomes away from the old central clump. These are the plants that will flower next year. The old central rhizomes should be discarded, its job is done, it won’t flower again.
Cut off the leaves to form a ‘fan’ shape about 150-200 mm high. Doing this will reduce the chance of the new plant ‘rocking’ on the surface on the soil, which will cause the roots to repeatedly snap as they try to grow.
Replant the new rhizomes in a shallow hole, making sure you don’t cover the rhizome with soil.
To further reduce the chance of rocking, peg down the rhizome with a hoop of wire, or a tent peg.
This is an ideal time to feed the plants. Use a balanced slow release fertiliser, or bone meal.
You can now forget about it until next year when you should see a new flower spike start to form in Spring.
Can I divide in Spring?
You can divide plants in Spring, if there’s no further risk of frost.
Dig up the whole clump, split off the new rhizomes, as described above, but plant them up in pots. Water sparingly - on the dry side of damp, and keep them in an unheated greenhouse or porch until all chance of frosts has passed. When there is no further risk of frost, you can plant out in your beds.
You should peg down the rhizome to stop the plant rocking in the wind, which snaps off the roots and weakens the plant you’ve nurtured all winter!