Encouraging iris blooms

Next to my driveway is a "Mediterranean mound" bed with Irises and Agapanthus, among other things, growing beneath a Sweet Gum tree. In the three years that we've been in the house, only a couple of the Irises have ever bloomed; those that did were "California Gold" and right next to the trunk of the tree. The Agapanthus in that section of the bed haven't bloomed much, either. So my question is how to encourage the rest of the Irises to bloom. They look pretty healthy to me, but just don't seem interested in flowering. They are fairly crowded, although I tried to thin them a little last fall. These are naturalized plants that, to my knowledge, have never been lifted. We also don't get very cold here in the winter; could that be a factor?

Any advice anyone could give me would be greatly appreciated. Thanks in advance.

Jim

There are at least two reasons for iris to fail to bloom. Most common is
being planted too deeply and the other is not enough sunlight. You may
plant them under a deciduous tree, like the sweet gum, if you stay out
toward the drip line where they can receive sunlight before the leaves
begin. Next to the trunk would be iffy. This is true for my area. Some
others from the west may have a better idea.

If they've been in place for a long time without being dug, divided, and replanted, then they are probably much more crowded than you realize, and they have most likely exhausted the soil nutrients. Dig the bed out completely and reamend the soil with compost, alfalfa meal, and any fertilizers for which a soil test of the bed indicates a need. Divide the irises and replant the largest, unbloomed rhizomes, spacing them 18-24" apart to allow for increase without becoming overcrowded again too soon. Plant so that the tops of the rhizomes are level with or slightly below the soil surface. If you plant too deep, the irises will refuse to bloom. As oldgardenrose noted, locate the irises where they will receive as much direct sun as possible. Irises generally require a minimum of 6 hrs of direct sun a day in order to bloom well.

Irises often take a year or more to settle back in after being replanted before they resume a regular bloom cycle, though some may bloom next spring. You'll get your best bloom on irises that have been in place for 2-3 yrs.

Laurie

Laurie and Oldgardenrose,

Thank you very much for your advice. I'll give it a try.

Jim