Iris discovery: Siberian and Japanese

Gardeners are discovering that there's much more to the iris world than tall bearded varieties. Japanese and Siberian irises are rapidly gaining favor because they're almost trouble-free, have stunning flowers, and thrive wherever they get enough sun and ample moisture.

Unlike bearded irises, both these kinds produce clumps of leaves that are green and healthy from the time they emerge in spring until hard frosts hit in fall.

You can order rhizomes of both Japanese and Siberian irises this month for planting in October (some mail-order sources are listed below).

Japanese iris: what five centuries of breeding can accomplish

These iris can stop you in your tracks. With big (sometimes 10-inch) flowers in a number of exotic variations on the fleur-de-lis theme, Japanese iris begin blooming when bearded irises stop, and continue through June and July. Colors are usually purple, blue, white, pink, or burgundy-but there are spectacular bicolors, many of which are spotted, netted, doubled, or rufflied almost beyond imagination.

These iris have a reputation as water plants because they're so often grown near ponds (ancient Japanese breeders grew them on dikes beside rice paddies). Ideally, they should have plenty of extra water during spring and early summer, then more moderate amounts after bloom. (Like Siberians, these produce abundant stalks with few flowers on each.)

On a rich, moist, sunny site, Japanese iris multiply quickly. We saw one 5-foot-wide clump in a Bellevue, Washington, garden; it had been started four years ago from six rhizomes.

That runaway-train growth rate can work against them: when clumps get crowded, plant health and flower size suffer. To keep plants healthy, divide fast-growing clumps every three to four years, slower-rowing clumps less often.

Fertilize plants every season, and top-ress with manure every winter.

The Siberians: easy, versatile, permanent, and oh, what colors

A diverse lot, the Siberians comprise several species and scores of hybrids (all from Asia but almost none, ironically, from Siberia). In bloom, they have some of the best purple, blue, and burgundy colors of any iris; there are even good yellows and whites. Out of bloom, their tall (30- to 60-inch) grassy foliage stands in beautiful contrast to most other garden shapes.

When you shop for these, you'll likely come across some kinds marked diploid or tetraploid. The tetraploids are hybrids with larger flowers and more substance

than standard diploids . But that's not to minimize the diploids; some, such as the award-winning pale blue Cambridge', have colors you just won't find in tetraploids.

Siberians do well on the same watering regimen as most other perennials, but if you give them extra water (I to 2 inches per week) during spring, they can grow an extra foot over the course of the season.

These plants tend to be tough and longlived; once you have them in the ground, you may not have to divide and replant for seven years. They also bloom profusely; you won't get more than two or three blooms per stalk, but you may get 50 or more stalks from a well-established plant, so the total effect is striking. Siberians bloom in May, at the same time as tall bearded irises, and make excellent cut flowers.

Mail-order sources: three in Oregon, one in California

You can occasionally find both Japanese and Siberian irises in retail nurseries, but your best bet is to get them from mail-order specialists. These ship during September, so order quickly.

Three of the best sources are in Oregon. They are Caprice Farm Nursery, 15425 S.W. Pleasant Hill Rd., Sherwood 97140 (40 Japanese, 6 Siberians; catalog I); Chehalem Gardens, Box 693, Newberg 97132 (45 Siberians; price list free); and Laurie's Gardens, 41886 McKenzie Highway, Springfield 97478 (162 Japanese, 66 Siberians; for a price list, send a 25-cent stamp).

Smith & Hawken's free bulb catalog lists six Japanese and five Siberian named varieties. Write to the firm, 25 Corte Madera, Mill Valley, Calif. 94941.