Few flowers can boast the diversity and distribution of the Iris genus. This hardy perennial truly deserves its moniker that comes from the Greek goddess of the rainbow, for irises come in every color of the rainbow and then some, offering quirky black and brown hues for those who long for something different in their garden designs. Irises also tolerate a wide range of growing conditions, adapting to habitats on every continent except for Antarctica. Explore this genus of over 300 species, and you will find a perennial for steamy, swampy spots as well as dry alpine gardens.
Why is the iris such a multifaceted and versatile flower? Perhaps it's because the iris evolved around 82 million years ago, giving the plant ample time to diversify, making it possible to deliver so many colors and forms to our landscapes. With the help of modern hybridizing, even more exciting new cultivars are made available each year.
- Botanical Name: Iris genus
- Common Name: Bearded iris, Siberian iris, Japanese iris, Dutch iris
- Plant Type: Hardy perennial
- Mature Size: Eight to 38 inches
- Sun Exposure: Full sun to dappled shade
- Soil Type: Average with good drainage
- Soil pH: Neutral to slightly acidic, 6.8-7.0
- Bloom Time: Spring to summer
- Flower Color: Red, orange, yellow, blue, purple, brown, white, black, pink
- Hardiness Zones: 3-9
- Native Area: Southern Europe and the Mediterranean
How to Grow Iris
The most popular of the irises, bearded irises, are easy to grow provided that you plant them in a sunny site with well-drained soil. Plant irises in late summer, when they are finished actively growing. One major departure of growing irises compared to other perennials: They do not like mulch. Mulches (as well as deep planting) encourage the rhizomes to develop rot, so let your soil remain bare. Space plants at least 12 inches apart to prevent the need for frequent dividing.
Irises need full sun to thrive. Irises in full shade produce fewer blooms and may suffer from an increase in diseases.
Heavy clay soils do not work well for iris growing. Sandy soils are excellent, but if your native soil is heavy, you can plant irises in raised beds to help drainage. You may also amend your soil with gypsum or organic matter like compost to lighten the soil.
Although irises like moisture, they need good drainage to go with it to prevent rot problems. Water them when the top two inches of the soil feels dry.
Temperature and Humidity
Irises are notorious for their hardy disposition. They don't mind temperature extremes, as long as the soil allows excess rain or snow melt to drain away.
In the spring, apply a low nitrogen 6-10-10 fertilizer around your irises. Too much nitrogen will encourage foliage at the expense of blooms. Bone meal is also a good fertilizer.
Potting and Repotting
For irises growing in containers, plant up in a loose soil-free potting mix. Irises in containers may need dividing and transplanting more frequently than those growing in the ground, about every other year or so.
Dividing irises will not only yield more plants for your garden, but it will also keep your existing irises healthy and vigorous. Dig rhizomes in August, and cut them apart, making sure each rhizome has one foliage fan. Divide irises every three to five years.
Varieties of Iris
Craving early blooms? Petite purple Iris reticulata bulbs bloom with the crocus and snowdrops in March. If you equate brown flowers with dead flowers, behold the bronze beauty of the 'Terre de Feu' bearded iris. Two-tone 'Panama Hattie' adds curbside appeal. Yellow flag iris is a sure bet in wet soils.
Toxicity of Iris
Irises are toxic to cats and dogs, especially the rhizomes. Consumption can cause vomiting, diarrhea, and lethargy.
Trimming back foliage fans to about six inches in the fall makes the garden look tidy, reduces leaf surface area that might host fungal disease, and removes caterpillar eggs. Destroy all foliage that you remove, and do not add it to the compost bin.
Being Grown in Containers
You can grow irises in pots 12 inches or greater. Leave the tops of the rhizomes exposed, and don't overwater the plants.
Common Pests and Diseases
The iris borer is the most serious insect pest of irises. In the spring, caterpillars hatch and tunnel through leaves, reaching the rhizome by summer. Feeding tunnels allow the rhizome to become infected with bacterial rot, compounding the damage. Remove all iris leaves after frost, and you will remove caterpillar eggs as well.
Iris vs. Gladiolus
Both members of the Iridaceae family, irises and gladiolus flowers both have large showy flowers in a wide range of colors and strap-like foliage. However, the gladiolus is a tender perennial and will not return in zones colder than 7. Gladiolus flowers grow in groups staggered along a single stalk, making them valuable cut flowers.