Divide and conquer for a more vigorous crop of irises

Sometimes the hardest part of gardening for me is summoning the enthusiasm to go out and work on my own plants. After landscaping all week for my clients and then talking on the radio about other people's gardens, it seems like the last thing that I want to do is to head out to the yard with a shovel and a rake and get some work done.

It is a testament to the bearded iris that I seldom begrudge the time it takes to keep a bed of iris looking and growing its best. True, they certainly are not the fussiest of plants, yet like all blooming, living things, they respond to timely care as much as any other member of the garden.

If your iris have been giving you diminishing returns lately as to the number and the quality of blooms, it's time to take a close look to see if they are overcrowded and in need of division.

Division needs to be performed every two to four years, depending on the vigor of your plants and how closely you replant. When looking at the rhizomes, if they are tangled to the point where it is hard to see individuals, and they are crawling over and pushing one another, it's time to divide and reset.

Mid-July through August is just about the perfect time to work on them. Any earlier and they most likely will not have formed roots on the new sections of growth that you are going to save, and any later you run the risk that they won't root down before the cold weather hits. In reality, I have dug irises in the fall and clumsily stored them over winter and still had blooms the following spring. But I don't recommend that schedule.

The first step is to dig and lift the overgrown clumps. Start about 6 inches outside the group and sink your spade from 4 to 6 inches under the clump and undercut an area approximately 12 to 18 inches square. From underneath, pry this clump up and out of the ground. Be careful not to cut into the rhizomes. Since the plants grow right at ground level, this will be the easiest lifting that you'll ever perform. Maybe that's why I like to work on my iris!

Gardening books often will recommend that you wash the soil off the roots at this point. I don't do that. It's messy and muddy and unnecessary. If the soil is dry, it will fall off the roots as you gently pry the rhizomes apart with your hands. And you won't be standing in muck.

Once separated, cut the strap-like leaves back to approximately 6 inches. This way you can see what you're doing and the plant will have a chance of standing up without falling over when you replant. Use very sharp shears for this.

Carefully inspect the rhizome for signs of soft rot and borers. Soft rot will look exactly like what it sounds like. Cut away and discard any infected sections. Borers will leave holes in the rhizome. Cut away any affected sections past any visible tunneling. On healthy rhizomes, cut out and discard all but the last section that contains the now shorn leaves. This is what you will plant.

Now is your opportunity to improve the soil before re-planting. I have had iris really resent being mulched, so this is the time to incorporate organic matter into your soil if it needs it. Certainly, irises don't need the fertility that many other perennials do, but if your soil is really poor, add amendments now. Adding some bonemeal may help the plants root faster and deeper.

The last caveat involves planting depth. The rhizome should never be fully covered with soil or it will likely fail to bloom. I like to barely bring soil to the top of the rhizome before I water it in. Half of it will be exposed after the soil settles. This is what you are shooting for.

Dividing your iris now will pay huge dividends next spring and for several years. After all, it's not like you have anything else to do at this time of year, right?

Stan Mapolski, aka The Rogue Gardener, can be heard from 9-11 a.m. Sunday mornings on KMED 1440 AM and seen on KTVL-TV Ch. 10 every Wednesday during the 5 p.m. news. Reach him at stanmapolski@yahoo.com.

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