Q: When should iris be dug up and replanted? Is it based on the calendar – a certain time of year – or condition of plants? They don't seem to die back enough for that. Or what other criterion should I use?

Our irises haven't been dug up for some years, so they probably should be attended to now.

– Lee Shore, Sacramento

A: When your iris clumps get crowded, it's time to divide and replant, says UC Master Gardener Annie Kempees. The buildup of pests and disease organisms and the depletion of vital nutrients may weaken your plants, resulting in fewer rhizomes reaching blooming size.

About four to six weeks after the flowers have finished blooming is a good time to dig up and divide a clump. At that point, the plants are beginning to enter a period of partial summer dormancy. Leaf and root growth slows or stops altogether.

The objective is to divide and reset the plants before a second growth of root production begins in late summer and autumn.

Just before digging, cut the leaves in an inverted "V" pattern, then remove the clump with a spading fork.

Wash off the dirt and inspect the plants. Choose only those rhizomes from the margins that are plump and healthy with a broad fan of leaves.

Break (rather than cutting) the healthy ones away from those that are spent and dispose of the latter.

Thoroughly wash the new divisions and allow them to dry completely for several days in a shady, airy place, on a layer of newspaper. Remember that they are near dormancy so no harm will be done.

Add 4 to 6 inches of compost or leaf mold, turned into the soil each time you replant.

When replanting, give the leaves a final trim. Trim off about two-thirds of the length of the roots.

If you have named varieties, label the fans with a permanent felt-tip marker. Lastly, replant the single divisions.

When dividing, remember: Each rhizome will bloom only once in its lifetime. After it flowers, the mother rhizome produces new baby rhizomes. That plump new growth is where the new flowers stalks will sprout. That's why you concentrate on saving those babies.

In addition to midsummer transplanting, bearded iris may be divided and transplanted in the fall, especially varieties that rebloom in late summer.

According to the Sacramento Iris Society, clumps of bearded iris should be divided about every three years for best bloom.

Q: There is a grasslike ground cover that I have seen planted in various locations. UC Davis Medical Center uses this ground cover. It looks like grass, but it is longer and willowy. Please tell me what this is and the upkeep on it.

– Shelley Johnson, Citrus Heights

According to UC Master Gardeners Bill Pierce and Carol Rogala, your mystery plant looks like a fescue (Festuca) that is not mowed.

There are several varieties of this grass on the market and it is sometimes sold as sod. The UC Davis Arboretum also has several examples in its collection and offers some fescues – including the native California fescue – at its nursery sales.

Fescue is a cool-season grass and is adapted to a wide range of conditions. However, it prefers well-drained, rich, organic soil, full sun to part shade.

Sow seeds or sod in the early fall for best performance. Mow it high for lawns (l 1/2 to 3 inches). If left unmowed, it provides a meadowlike appearance.

Irrigate thoroughly and deeply and not again until the turf indicates a need; usually every two weeks.

Tall fescue is a cool- season grass that is well adapted to sunny or partially shady areas. This low-maintenance turf grass will tolerate moderate traffic and infrequent mowing.

Tall fescue is a good species to plant for general lawn use and is the most common lawn grass in California.GARDEN QUESTIONS?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.

Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put "Garden Detective" in the subject field and include your postal address. To contact your UC Extension directly, call:

• Sacramento: (916) 875-6913; 9 a.m.-noon and 1-4 p.m. weekdays

• Amador: (209) 223-6838; 10 a.m.-noon Monday through Thursday; email ceamador.ucdavis.edu

• Butte: (530) 538-7201; 8 a.m.-noon and 1-5 p.m. weekdays

• El Dorado: (530) 621-5512; 9 a.m.-noon weekdays

• Placer: (530) 889-7388; 9 a.m.-noon on Tuesdays, Wednesday and Thursdays or leave a message and calls will be returned

• Nevada: (530) 273-0919; 9 a.m.-noon Tuesdays through Thursday or leave a message

• Shasta, Tehama, Trinity: (530) 225-4605

• Solano: (707) 784-1322; leave a message and calls will be returned

• Sutter, Yuba: (530) 822-7515; 9 a.m.-noon Mondays and Tuesdays and 1-4 p.m. Thursdays

• Yolo: (530) 666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned

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