Gardening Articles: Flowers :: Bulbs
May's Flower: Bearded Iris (page 2 of 4)
by National Gardening Association Editors
Where and How to Plant Bearded Iris
Container-grown iris are less susceptible to transplant stress.
These flowers' popularity is explained in part by their being widely adaptable and easy to grow throughout most of North America. The only exception is the humid subtropics. For instance, they're fine from Bangor, Maine, to San Diego, California, but not in Houston, New Orleans, Miami, or Savannah. However, they do grow well a little farther north in the southeast (Shreveport, Birmingham, and Atlanta). Generally, iris grow in USDA Hardiness Zones 3 through 10 in the dry-summer West and in 3 through 8 in the rainy-summer East.
Most iris need at least 6 hours of full sun, and good drainage. In deeply cultivated, rich soil, they respond with superior growth and flowers. A soil pH near neutral is best. Sand or clay soils are okay, but you need to pay more attention to drainage in heavy clay soils. If water in your garden pools for more than half an hour after a rain, plant in raised beds or mounds.
In cool maritime regions like Seattle and Boston, day-long full sun is required, but in hot regions, such as Phoenix or Dallas, locate plants so they receive afternoon shade.
Set out plants anytime between midsummer and a month or so before first frost: July to October in most regions, July and August in coldest climates, and September and October in hottest climates. You have somewhat more latitude in transplanting container-grown iris as they suffer less stress in the process.
Whether you buy plants by mail or are the beneficiary of a generous neighbor, what you put into the ground looks the same: a 1/2-inch-thick, 2- to 3-inch-long fleshy rhizome with short, spaghetti-like roots spreading from its sides, and a short fan of leaves at one end. The rhizomes are tough enough to stay out of the ground for a week or two without serious harm, but the sooner they are planted, the better.
Amend the soil with generous amounts of compost or peat moss, and add 2 pounds of 5-10-10 fertilizer for every 100 square feet of garden. If your soil tends to be acidic, add ground dolomitic limestone to raise the pH to nearly neutral. (Use a soil test to determine your soil's pH and the type and amounts of amendments necessary.)
Space rhizomes 1 to 2 feet apart, or closer for a more immediate effect and for dwarf varieties. However, close planting usually means sooner replanting. Set each plant in a shallow hole large enough to accommodate the division and the attached fibrous roots. Because new plants will emerge from the fan end and sides of the rhizome, orient the leaf end in the direction you want to growth to take.
If you're planting several iris of the same variety, arrange them in drifts with the fans all pointing in the same direction, or plant in a circular clump with fans pointing outward.
Cover the rhizomes with only 1/2 inch of soil. Depth of planting is particularly important in heavy clay soils where drainage may be impeded. Water to settle the soil and start growth, then water sparingly until new growth indicates that roots are growing.
Plants need regular water throughout the growing season, but especially until six weeks after flowers fade. It's during this period that the next season's growth is initiated. Established clumps are drought tolerant and don't need water except in areas where there's little rainfall.
Lightly mulching new plantings is important. It prevents sunburn in the hottest regions. In the coldest regions, it prevents freezing and thawing of soil, which can kill the shallow-rooted plants.