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Bearded irises don't bloom? Time to divide

Blue irises
These blue irises are family heirlooms and have been blooming consistently for more than a century -- divided and replanted all along the way. (Photos: Debbie Arrington)

This easy-care perennial benefits from division, replanting

Divide and bloom; that’s the secret to bearded irises.

They’re such a persistent (and fast-growing) perennial, they need to be divided every three years or so. Otherwise, their rhizomes – their thick fleshy roots – overcrowd each other. If too crowded, they don’t bloom.

If your bearded irises have not bloomed in more than a year (but still look relatively healthy), they likely need to be divided.

Traditionally, August is the best time to divide and replant irises in Sacramento. With a slight break in the heat and smoke expected later this week, now may be a good time to tackle your iris beds.

Division and replanting are the only major work these easy-care plants need. So, a little TLC now will pay off for years to come.

Dig up the main clump; some rhizomes will look old and withered. Cut those off and discard. The other segments can be cut or broken apart. Make sure there’s at least one “fan” of leaves on each segment to be replanted. Trim the leaves to about 4 to 6 inches long. And, if you know, write on the leaves the iris variety or color. (A Sharpie works well for this.) This helps keep them sorted when you replant – and when you share irises with friends.

Preparation of the planting bed will assure beautiful blooms for several seasons to come. Even though irises are planted very shallow, dig down at least 10 to 12 inches and work the soil, breaking up any large clumps. Spade in some well-aged compost and bone meal to promote big flowers and root development.

Bronze irises
These bronze irises are eye-catching. In Sacramento, irises are
best divided and replanted in August.

Irises appreciate good drainage and full sun. If your soil is heavy clay, add some coarse sand along with the compost and bone meal. Don’t use high-nitrogen fertilizers on irises; it promotes lots of leaves but no flowers.

To replant, form two parallel trenches with a ridge down the middle. Put the rhizomes on top of the ridge with their stringy roots running down into the trenches on either side. Space each rhizome about 12 to 18 inches apart.

The plants will grow (and rhizomes increase) in the direction the fans of leaves are pointing. Arrange the rhizomes so their fans are all pointing (at least generally) the same direction; that keeps them from overcrowding too quickly. If arranged in a circle, place the fans pointing away from the center.

Once placed, gently press the rhizomes into that ridge, making sure the top of the rhizomes will be just above soil level. Then, fill in the side trenches with soil.

Water deeply – and wait. The rhizomes will start producing fresh leaves in early fall. Water the plants occasionally so they don’t dry out, but otherwise leave them alone.

And remember to share some of those freshly dug irises with friends. One large clump can produce several new plants – many more than is needed to replant the same space. Those extra rhizomes should be replanted within two weeks.

For more on irises: .


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Garden Checklist for week of July 7

Take care of garden chores early in the morning, concentrating on watering. We’re still in survival mode until this heat wave breaks.

* Keep your vegetable garden watered, mulched and weeded. Water before 8 a.m. to conserve moisture.

* Prevent sunburn; provide temporary shade for tomatoes, peppers, eggplant, melons, squash and other crops with “sensitive” skin.

* Hold off on feeding plants until temperatures cool back down to “normal” range. That means daytime highs in the low to mid 90s.

* Don’t let tomatoes wilt or dry out completely. Give tomatoes a deep watering two to three times a week. Harvest vegetables promptly to encourage plants to produce more.

* Squash especially tends to grow rapidly in hot weather. Keep an eye on zucchini.

* Some weeds thrive in hot weather. Whack them before they go to seed.

* Pinch back chrysanthemums for bushy plants and more flowers in September.

* Harvest tomatoes, squash, peppers and eggplant. Prompt picking will help keep plants producing.

* Remove spent flowers from roses, daylilies and other bloomers as they finish flowering.

* Pinch off blooms from basil so the plant will grow more leaves.

* Cut back lavender after flowering to promote a second bloom.

* One good thing about hot days: Most lawns stop growing when temperatures top 95 degrees. Keep mower blades set on high.

* Once the weather cools down a little, it’s not too late to add a splash of color. Plant petunias, snapdragons, zinnias and marigolds.

* After the heat wave, plant corn, pumpkins, radishes, winter squash and sunflowers. Make sure the seeds stay hydrated.

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