How to Grow and Care for Iris Flowers

Iris plants

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In This Article

There are around 300 varieties of flowers in the Iris genus. These famous flowers are available in two main forms: those that grow from rhizomes and those that grow from bulbs.

Iris flowers feature unique blooms that are made up of two different kinds of petals, falls and standards. The falls form the outer petals, which droop downward or fall. The standards stand upright. The characteristics of an iris petal further segment the plant into three types: bearded, crested, and beardless. Bearded iris plants have soft hairs along their falls, resembling a beard. The flowers of a crested iris have a ridge-like crest on their falls. Beardless have neither hairs nor crests.

Irises that grow from bulbs include the dwarf and Dutch varieties and often bloom a bit earlier than the rhizomatous irises. However, most show their famous flowers in the early summer, while some also bloom for a second time in the late summer. They are known for attracting butterflies and hummingbirds and make perfect cutting flowers. The iris varies greatly in size from the smallest dwarf variety, which only grows to 6 inches tall, to the tallest variety which is up to 4 feet tall. 

Botanical Name Iris
Common Name Iris
Plant Type Perennial
Mature Size 6 in. to 4 ft. tall
Sun Exposure Full sun
Soil Type Rich, moist, well-draining
Soil pH Neutral to slightly acidic
Bloom Time Late spring, early summer, and late summer
Flower Color Varying shades of purple, blue, white, yellow
Hardiness Zones 3 to 9, USA
Native Area Europe, Asia, North America
Toxicity Toxic to humans, toxic to pets
Bearded iris plant
Example of a bearded iris Juan Rosillo / EyeEm / Getty Images 
Crested iris variety
Example of a crested iris flower GracedByTheLight / Getty Images
Crestless iris flower
Example of a crestless iris flower Ivan Petermann / EyeEm / Getty Images

Iris Care

When planting irises, it is best to do so in late summer or early fall before nighttime temperatures fall below freezing. This allows the plant time to become established and enter dormancy for the winter. When planting, be sure not to bury the rhizomes too deep into the soil. Though they look tender, iris rhizomes need to be just below or at ground level and slightly exposed to the elements. If you live in a very hot area, you can cover them slightly, but not deeply.  

Once flowers are spent, deadhead the blooms. When the whole stalk of flowers is spent, cut the stalk to the ground to keep your iris healthy and neat. Once the first heavy frost comes or your leaves yellow for the season, you can cut your iris foliage to the ground to prevent iris bores from overwintering in the leaves. However, do not be tempted to remove the foliage before then, as the greenery is still performing photosynthesis, providing the plant with energy necessary for next year’s blooms.

Once the foliage is trimmed back for the winter, be sure to cover the rhizomes with something to help protect them, such as sand or mulch. Remove this in the spring. Irises are a great choice for areas with wildlife as they are deer resistant. Common pests include iris borers.  

Light

Most iris varieties do best in full sun. They can tolerate partial shade, but too much shade will prevent them from flowering. 

Soil

Rich, well-draining soil is best for iris plants. Though they like moist soil, too much water can be damaging. If you are worried about too much standing water, try planting your irises in raised beds, as this will allow for optimal water drainage. 

Water

Because the iris likes both moisture and well-draining soil, watering consistently and deeply is very important. Just be sure not to overwater, as too much water in the soil can cause problems such as root rot. Though they appreciate consistent water, irises are drought-resistant and won’t die quickly if they are deprived of water for a short time. 

Temperature and Humidity

With its wide range of varieties and growing zones, the iris is a hardy plant that can tolerate fluctuations in temperature and humidity. As long as the soil is well-draining and they get plenty of water and sunshine, these flowers can thrive in a large variety of gardens.  

Fertilizer

Because irises prefer rich soil, compost makes a perfect fertilizer. Loosening the soil in the spring and adding a healthy layer of compost will help give your irises the nutrients they need to grow healthy and lush.

If you do not have compost, a well-balanced fertilizer for flowers works well. Just beware of too much nitrogen, which can lead to rot. Because some varieties bloom twice, once early in the season and once later in the season, these varieties will appreciate another dose of fertilizer before their second bloom.   

Is the Iris Toxic?

Though beautiful to look at, the entire iris plant is toxic if ingested. The rhizomes or bulbs are the most toxic part of the plant. The sap can also cause skin irritation.

Symptoms of Poisoning

Symptoms of poisoning are usually milder in humans and cause digestive distress such as vomiting, nausea, and diarrhea. For curious pets who consume higher amounts of sap or ingest the rhizomes, symptoms can be more severe. According to the ASPCA, these include drooling, vomiting, diarrhea, and lethargy.

Iris Varieties

  • Yellow Iris: Also sometimes known as "flag," this variety of beardless iris is highly tolerant of moisture. It is an abundant spreader, which sometimes deters gardeners from planting it. However, it makes a great container flower variety and produces beautiful blooms and bright green foliage.
  • Louisiana Iris: This iris is native to the U.S. and hardy up to zone 4. They boast a wide variety of colors and petals that are reminiscent of lilies.
  • Japanese Iris: The Japanese iris boasts large, broad petals, and a stunning array of colors. This variety also does well with increased soil moisture, making it the perfect choice in areas with high water tables or a greater chance of standing water. 
  • Siberian Iris: The Siberian iris provides smaller, more delicate-looking blooms than many other iris species and adds a beautiful pop of color in the late spring.  

Propagating Irises

Irises spread underground through rhizomes or bulbs and will need to be divided every 3 to 5 years, creating the perfect opportunity to spread your irises to new landscaping areas. You will know when it is time to divide when you have fewer blooms or there are rhizomes popping out of the ground. Follow these basic steps to propagate iris plants:

  1. Wait for 6 to 8 weeks after your irises have finished blooming. Then, with a garden fork or shovel, slowly work around each plant to loosen the rhizomes or bulbs. 
  2. Gently lift the iris out of the ground and shake out the dirt. 
  3. Once the dirt is removed you will be able to see the rhizomes or bulbs. You will find smaller rhizomes spreading from the larger mother rhizome. Some may come away naturally while others will need to be cut. Either way, divide these smaller rhizomes and toss any old, shriveled rhizomes. 
  4. Once you divide the rhizomes and remove any that are spent or diseased, simply plant the divided iris plants in a new location.