Darlene F. of Sonoma asks: My bearded irises used to bloom beautifully. This year there weren’t many blooms. They are in full sun, get plenty of water and they’re growing in good soil. There are a lot more plants now since I planted them 5 years ago. A friend told me I needed to divide them. If so, how and when do I divide them?
The first indication that your bearded irises need to be divided will be the decreased blooming. Overcrowded iris rhizomes will produce fewer and fewer flowers compared to uncrowded iris rhizomes. It’s also time to transplant your irises if and when the rhizomes start heaving out of the ground and look like they’re growing on top of one another.
Overcrowded iris rhizomes will start to grow into each other, which causes the root system of the iris plants to start pushing themselves out of the ground and you can see the mass of roots growing all over.
The best time to transplant bearded irises is late summer, after the iris have finished blooming, up until late fall.
To divide your irises, lift the clump of plants out of the ground with a spade or fork. Try to lift the whole clump in one piece, but if you can’t, carefully break the clump into smaller pieces and lift them out.
Brush off as much soil as possible from the rhizomes. This will make it easier to see where to break the clumps apart.
Each iris rhizome will then be divided into pieces and have at least one fan of leaves on each rhizome. Do not remove the roots from the rhizomes.
As you get closer to the center of the clump, you may find sections of rhizomes that are shriveled up and/or dead, with no roots attached. Throw those away. Check the iris rhizomes for borers and disease.
The iris rhizomes should be firm, and not soft and squishy. If they are, throw them away.
Once you have divided the iris rhizomes, now you can replant them. Some gardeners set the divided rhizomes out in the sun for a couple of days, giving the cut sections time to callus over. You don’t have to do this if you’re in a hurry to get them planted. First, trim the leaf fans back to about 6 inches tall. This will allow the plant to grow new roots without having to support a large amount of foliage at the same time.
Plant the iris rhizomes in soil that has been amended with a little organic matter. If you are going to plant some in a different location, be sure the area is also in full sun. Set the rhizome into the ground just below the ground level, horizontally, with the leaves pointing straight up.
If you are going to plant several irises near each other, point the rhizomes away from each other and space them about 12 inches apart.
Spread the roots out around the rhizome and then cover the roots and the rhizome with soil. Water them well and keep them damp, but not soaking wet all the time.
Gene F. also from Sonoma asks: It’s getting to be that time of year when we will be planting the spring blooming bulbs. Before I buy any, do you have any guidelines for buying good quality bulbs? What should we be looking for? I have been disappointed in the past with small blooms and lack of blooms.