Last Updated on September 16, 2022 by Plant Mom Care
Iris is the major genus of the Iridaceae family, famous for the showy flowers produced by more than 300 species, including hundreds of hybrids in the genus. While some authors claim that the name denotes the wide array of flower colors found among the species as well as other species belonging to closely related genera, others say the genus is named for the Greek rainbow goddess Iris. She passed along messages from the gods to earth on a rainbow and beautiful flowers of all colors bloomed wherever the rainbow landed.
The earliest artwork dedicated to the goddess is a mural found on Crete dating approximately 2400 BC. King Thutmose III of ancient Egypt grew Syrian irises and had artists engrave images in stones of a Temple of Amon.
Almost all plants in the species are from Northern hemisphere temperate zones in Asia, Europe as well as North America. These plants predominantly grow in arid, semi-desert, grassy slopes, cold rocky mountainous areas, bogs, meadowlands, and riverbanks.
They vary in size, from varieties that grow only 6 inches tall to taller varieties that grow to 4 feet. They are further classified by varieties that grow from rhizomes or bulbs. They all have erect simple or branched flowering stems, hollow or solid and flattened or circular. The rhizomatous varieties generally have 3–10 sword-shaped basal leaves that form dense clumps while the bulbous varieties with cylindrical basal leaves.
The flowers are distinctive and composed of two types of petals – standards and falls, standards are 3 upper petals while the lower petals are called falls that droop downwards or fall. The features of the petals further divide the plants into 3 types – crested, bearded, and beardless. Bearded plants produce soft hair on their falls, like a beard while beardless plants don’t have hairs or crests like the crested plants that have a ridge-shaped crest on the falls.
Plants growing from bulbs usually flower earlier than rhizomatous plants. However, most display their celebrated flowers in early summer, while others also flower again in late summer. They attract several different pollinating insects and hummingbirds and make perfect flowers for bouquets.
They are extensively cultivated as ornamentals in botanical and home gardens. The Presby Iris Gardens of New Jersey, USA is a living museum with over 10,000 iris plants, whereas the Giardino dell’Iris of Florence, Italy is Europe’s most well-known iris garden that hosts an iris breeders’ competition every year. Irises feature frequently in flower shows like the famous Chelsea Flower Show.
Irises Light Requirements
Most varieties grow best under full sun. A few varieties can tolerate partially shaded conditions, but excessive shade will stop them from blooming.
These plants like water and well-drained soil, so it’s necessary to water them consistently and deeply every 7 or 10 days or as required in the morning or evening. Don’t over-water them as most varieties are drought-tolerant and water-logged soil causes root rot. Though they need constant watering, they won’t die if they aren’t watered for a while.
They prefer average humidity levels of approximately 40-50%.
They like average temperatures between 60-75°F. However, considering their wide range of growing conditions and varieties, these plants are hardy and can tolerate fluctuations in humidity and temperature.
Rich, well-drained soil is best for these plants. As mentioned, although they like damp soil, excess water can damage them. Try planting them in raised beds, as this helps provide good water drainage.
If your plants grow in pots and no longer flower as they once did, it’s an indication for repotting them after dividing the rhizomes or bulbs. Use 6- or 8-inch pots for dwarf varieties and 12-inch ones for taller varieties and make sure your pots have good drainage capacity. After flowering, remove and divide the plants in July and they will reward you with more flowers next year.
These plants are usually propagated by seeds and division. However, to get flowers next year, rhizome or bulb division is the best method to use. While propagating from seed can also work, germination rates are usually low as 50% and it might take 2 to 3 years for the plants to flower. Furthermore, seeds from hybrids won’t grow true as the parent plant.
Rhizomes/bulbs can become over-crowded, inhibiting flowering, and should be divided every 3 to 5 years after the flowering season ends in July. Using a digging fork, dig around the plant to uproot the rhizome/bulb clumps. Carefully lift the clumps and remove excess soil.
Separate them by hand, choosing only healthy specimens and discarding any that are rotting, soft, or showing signs of insect damage. Treat the cut rhizomes or bulbs with a suitable fungicide. Once this is done, simply plant the divided rhizomes or bulbs into pots or another location in the garden.
Because they prefer rich soil, adding compost is a perfect amendment to help give your plants all the nutrients they require to grow healthy. However, if you don’t have compost, a balanced fertilizer designed for flowers will work as well. Just make sure it doesn’t contain too much nitrogen – this might lead to rot. If the varieties you’ve planted bloom twice in the season, add another fertilizer dose after they finish with their first bloom.
Remove seed pods to prevent overcrowding. After flowering, prune back flower stalks but keep the leaves in place to produce and store energy for the next year. Cut any brown tips if necessary by autumn, leaves naturally brown and die off and can be cut back to prevent disease and pests during winter. Plants growing in cold regions require mulching with leaves or straw which must be removed when new growth emerges in spring.
Irises Common Problems
Aphids suck sap from foliage and can spread disease. Get rid of them with strong sprays of water larval borers of certain species of moths target the rhizomes of some species. Inspect rhizomes regularly for holes or check for water-soaked leaves any plants found with these signs should be discarded. Caterpillars can munch on the foliage but are easy to control by handpicking, slugs and snails also like to munch on flowers and leaves and create irregular holes. Handpick and dispose of these pests and remove any hiding places like stones and garden debris. Apply diatomaceous earth to restrict their access.
Soft rot initiated by the Erwinia carotovora bacteria could be a problem and usually happens in warm and wet springs. Symptoms include wilting and decay at leaf bases and soft, smelly rhizomes. When soft rot attacks, use a spoon to scoop out infected portions of the rhizome and then dry the rhizome in the sun for several hours, dust the rhizome with garden sulfur before replanting.
Sclerotium rolfsii causes fungal crown rot by covering rhizomes and the leaf bases with a soft gray mat causing decay and usually appearing under warm and wet conditions. To avoid crown rot, keep garden beds clean, use sterile tools for dividing rhizomes, and immediately remove infected material. If this is a frequent problem, disinfect rhizomes by plunging them in a bleach solution of 10% bleach to 90% water before planting
Cladosporium iridis fungi cause leaf spots that appear as water-soaked spots that combine, darkening to brown, and might have sooty-appearing spores in wet weather remove and dispose of plant parts infested by leaf spots.
Puccinia iridis fungi cause rust that shows up as light green or yellow spots with a rust-colored brown bump that turns black as leaves turn yellow and wither from the tips downwards. Remove and discard infected leaves to stop them from spreading.