Two Easy-Care Perennials Need Periodic Dividing in August 8/8/05

OLATHE, Kan. – This year’s hot and often humid summer weather doesn’t seem like the best time to garden. ...unless gardeners love irises or daylilies.

In early to mid-August, both long-time perennial favorites are in a kind of dormant period. So, that’s when gardeners are most likely to succeed in dividing the plants’ clumps. The clumps tend to become overcrowded and less productive every three to five years, said Dennis Patton, horticulturist with Kansas State University Research and Extension.

Some Irises Can Rebloom

OLATHE, Kan. – The iris – named for the Greek goddess of the rainbow – is attracting new interest because experienced gardeners and plant breeders are coming up with varieties that flower more than once. Under just-right conditions, some irises can now bloom from spring through fall.

“Called reblooming or remontant irises, these plants flower at the usual time in early to mid spring. Then some can put up new stalks within a month of the regular season. Some have a second flowering period in late summer or early fall. And, some are sporadic or everblooming – which means you can’t predict when they’ll rebloom, but if they like where they’re living, these irises may bloom repeatedly,” said Dennis Patton, Kansas State University Research and Extension horticulturist.

Apparently, all irises with rhizomes can develop varieties that are able to rebloom, Patton said. Among the bearded irises, that could include plants that range from 6 to more than 40 inches tall. Some of the “beardless” water and bog iris types can rebloom, too.

Thus far, however, the Reblooming Iris Society, a section of the American Iris Society, is still gathering data on the varieties that perform well in particular locales. For example, Kansans have reported success with six: Baby Blessed, Double Shot, Flower Child, Low Ho Silver, Perfume Counter and Rosalie Figge. Nebraskans, on the other hand, have achieved rebloom with 51 varieties.

“Plus, plant breeders are working on many more new varieties. So, the rebloomers, along with the newly popular dwarf bearded and beardless irises, are likely to remain big news in the garden world for years to come,” Patton said.

“For the most part, we’re talking about extremely easy-care plants. To keep them healthy and promote optimum flowering, however, you simply have to divide them periodically,” Patton said.

During dry weather, the horticulturist recommends watering overcrowded clumps a day or two before digging, just to make the process easier. Some gardeners also cut back the leaves by half to make handling the plants easier, too.

“After that, there is no simple approach. You’ve simply got to jump in and tackle digging up the entire clump,” Patton said. “Fortunately, though, irises have a fairly shallow root system. Daylilies’ roots can be harder to dig up, because they’re a little deeper and get more tangled with each other, but they’re also better able to handle some injury.”

If gardeners plan to move some divisions to other parts of their landscape, they should select sites that receive at least six hours of sunlight, he said. One reason irises and daylilies have maintained their popularity since pioneer days is that they tolerate most garden soils. Even so, the plants also prefer well-drained soil that is neutral to slightly alkaline.

Irises have fat food-storage structures called rhizomes that produce leaves and flowers above and roots below ground level. Gardeners must be careful with the leaves and roots, Patton said. But, they can assume the rhizomes are fairly tough and just knock away any excess soil, so they can see where to snap or cut the rhizomes apart.

The best iris divisions are sound rhizomes with two or more leaf-growing points.

“You’re always going to throw some rhizomes away. And, the first ones to discard are those with holes and worm-like insects called iris borers – which can seriously injure or destroy the plant. Then cut off any remaining affected tissue and dust what’s left with a garden insecticide, such as Sevin,” he said.

Rhizomes spread outward, forming a new “knee” or bump every year. The only necessary bump is the one that’s attached to the leaves. The others are no longer productive

Some iris lovers do leave one or two others to help stabilize the division in the soil more quickly. To discourage borers, however, they cut away the oldest rhizomes and discard them far from the iris bed.

Iris plants like well-cultivated soil, improved with organic matter. The traditional way to plant them there is the “hill in the hole” method, Patton said.

“Dig a hole that’s deep enough for the longest roots. Mound up a hill in the middle of that hole and place the rhizome on it, with the roots dangling down the hill’s sides. A rhizome must never be more than an inch below the soil line. In fact, it will be fine if its top surface stays a bit exposed to air and sunlight,” he said. “After that, fill the remainder of the hole and water. Wait until spring to fertilize.”

Daylilies Still ‘Tough Enough’

SALINA, Kan. – Time and weather have reduced most High Plains homesteads to rubble. Yet, stands of orange-blooming daylilies still often mark the homes’ entries.

“The old orange variety is tough,” said Chip Miller, horticulturist with Kansas State University Research and Extension. “But you can believe that most of the newer varieties with all of their unusual colors are also ‘tough enough.’”

Plant breeders have introduced more than 30,000 cultivated daylily varieties since the first one came on the garden scene in 1890, Miller said.

“Today, daylilies are available in every color except blue. They range from 1 to almost 4 feet tall. They grow in full sun to light shade in hardiness Zones 3 to 10,” he said.

Nowadays, neglected daylilies still tend to survive – no matter what their variety, the horticulturist said. They do better, however, if watered during droughts and separated into new divisions when they get crowded.

“Unlike many perennials, you can divide or just move daylilies about any time during the growing season – even while they’re blooming. Still, the best time tends to be just after their last flowers for the year have faded,” Miller said.

He’s turned one of his in-depth columns about daylily selection and care into a fact sheet that’s now available on the Web at http://www.oznet.ksu.edu/ckd3/_EzWeb/Newsletters/96097.pdf

Patton prefers planting iris divisions in groups of three, with their rhizomes nearly touching and the leaves on the outside of the circle. As they grow, the divisions will widen and thicken the circle.

Daylily lovers who regularly divide their plantings can sometimes use a spading fork to “peel off” a fan or two while an overgrown clump is still in the ground, the horticulturist said. But, the first step in dividing large, tightly packed clumps is to dig them up. After that, gardeners have three options for creating divisions:

* Wash away the clump’s soil. Roll the clump back and forth until divisions separate off.

* Use a sharp spade to cut the clump into pieces, thereby losing quite a few roots.

Patton said the best size for a daylily division depends on how fast the gardener wants an area to fill in. But, he doesn’t recommend replanting one that’s much larger than a head of cauliflower.

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.