Few plants provide so much beauty with so little effort as today’s iris hybrids. They're easy to plant, require minimum care, and multiply annually. These fast-growing flowers brighten gardens with an impressive array of blooms that increase yearly, and their sword-like foliage is attractive even when the flower isn't in bloom. An incredibly versatile plant, irises are excellent in the garden, bordering a walkway, or in a rock garden. The taller varieties are excellent as cut flowers and the Dwarf varieties are excellent for container planting.
Quick Reference Planting Guide
- Location: Full to partial shade, with at least five hours of direct sun per day.
- Hardiness: Will do well from zones 4 – 9 and survive temperatures to -30°F.
- Planting Distance: Miniatures and dwarfs 6" – 12" apart; border & bearded 1' – 2' apart; intermediates 2' apart; and tall bearded German iris 2' – 3' apart.
- Mature Height: Dwarfs, border and bearded, and miniature irises span a range of from 5" – 28" tall; intermediates 18" – 24" tall; and standard tall German iris 3' – 3-1/2' tall. They all attain their mature height by the second year and will form heavy clumps within three years.
- Bloom Time: Dwarfs, border and bearded, and miniature irises bloom first in the spring, then the intermediates, then the standard German varieties. They all bloom the first spring/summer after planting. If any varieties in these categories are offered as re-bloomers, they'll repeat bloom in August/September and sometimes into October/November depending upon weather conditions and your planting zone.
- To Plant: Dig shallow holes 10" across and 2" deep. Make a ridge of soil down the middle of the hole, dividing it in half. Place your iris rhizomes on the ridge, spreading the roots to cover both sides. Cover with soil and firm with your hands. In clay soil, rhizomes should be slightly exposed. In sandy soil, they can be covered with an inch or two of soil. Water thoroughly.
Irises do well in average well-drained soil of all types, but you can improve your planting success as follows:
- Spade or rototill the soil to a depth of 9" – 12".
- Mix in a 2" – 4" layer of dehydrated manure, garden compost, shredded leaves, and/or peat moss. After active growth begins, periodically feed with a water soluble flower booster. Plants in containers need more frequent water and feeding, especially when in active growth, bloom, or while setting fruit.
- Watering: Your plants require at least 1" of rainfall, or equivalent watering, each week. Whenever rainfall is minimal, be sure that you water well at least once a week, and more frequently during a drought or extremely hot weather.
- Mulching: Apply a 2" – 4" layer of shredded bark, compost, or other organic mulch around your plants to promote moisture retention, maintain even soil temperatures, and discourage weed growth.
- Weeding: Keep the area around your plants free of weeds. Weeds compete with all plants for food, water, and light. Walk around the garden periodically and pull weeds, including the roots, as soon as you see them. Mulch also assists in keeping weeds down.
- Deadheading: Remove spent blossoms to promote additional blooming. Pinch or cut off when they've faded, but leave as much foliage as possible.
- Grooming: Clip off unsightly or dead growth to maintain the plant's shape. Cut flower stalks between the bottom blossom and the uppermost leaves.
- Feeding: Discontinue any feeding after September 1. Your plants want to harden off for winter dormancy.
- Winterizing: After frost has blackened the foliage of your iris, trim them back to 3" – 5" and clean up the area around the plants. Apply a 4" – 6" layer of mulch. Gardeners in northern states should protect their irises every winter. If alternating freezing and thawing lifts your iris rhizomes, don’t try to press them back into the soil. Instead, just bank soil around the rhizomes and the exposed roots. As soon as the weather warms up, remove any mulch from in-ground plantings. At the same time, be sure to clean up the garden and remove dead or damaged parts on any plants.
- Containerized Plants: Move your containers to a sheltered location in northern zones, such as an unheated garage or shed, over the winter. You can also move containers to the south side of a foundation and mulch for the winter. Such warm locations can actually increase the hardiness factor by two planting zones. You can also bury or plant either the plant itself or the entire container in the garden and mulch after the ground has frozen. As soon as the weather warms up, remove any mulch from the container and bring it back out into the garden sunlight.
- Dividing: Irises can be divided every 4 – 5 years. August is the best time to do this. Older rhizomes that have few white roots should be discarded. Be sure each rhizome has one or two fans. Replant as you did your new iris.