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How to Grow Iris Plants in your Garden

Gardener's HQ Guide to Growing Iris and Flag

The Iris is a large genus of plants that include hardy perennials and hardy bulbs.

Due to the large size of the Iris plant genus they vary immensely in size, from 15 to over 180 cm (6 to 72 inches). This makes Iris ideal for all sections of the garden, and they make very attractive border plants.

Iris have sword shaped leaves and beautiful flowers of all colours and shades.

Iris
Iris Photograph by Lisa JG.

Iris Growing and Care Guide

Common Names: Iris, Flag.
Life Cycle: Hardy perennial. Half hardy perennial. Hardy bulb.
Height: 4 to 72 inches (10 to 180 cm).
Native: Northern Hemisphere: Europe, Asia, Africa, North America.
Growing Region: Zones 2 to 9.

Flowers: Species dependent: Spring/summer/autumn and/or winter.
Flower Details: Purple, brown, maroon, white, blue, yellow; many different pastel colours. Showy. Fan-shaped inflorescences. Six lobed.
white, red, pink, orange, yellow, green, blue, pink, lilac. Small. Clustered. Fragrant. Daisy-like ray and disc florets. Bell-shaped. Tubular. Trumpets. Inconspicuous pale green; plants are grown for their attractive silvery or bronze spearheads.
Foliage: Sword-shaped.

Growing Iris Outside: Bulbs: 2 to 5 inches (5 to 12 cm) depending upon species. Rhizomes: level to the soil surface. Early in autumn. Spacing: small 4 to 8 inches (10 to 20 cm); medium to large species 12 to 18 inches (30 to 45 cm).
Sowing Iris seeds: Germination time: one to eighteen months (sometimes longer).
Seed: Method 1: Seeds should first be sown into flats in the autumn or winter. Next sink the flat into the ground in an area that offers shade, preferably close to a wall that faces north. Provide a glass/plastic covering. Keep an eye on the flats to ensure that the soil remains moist. Bring the flats indoor at the beginning of spring and keep at 60 to 70°F (16 to 21°C).
Seed: Method 2: In the spring or summer, mix seeds in a moist growing medium, then put in flats, wrap in a large plastic bag, then stratify by refrigeration for three weeks. Next bury the flat as described above. Once seedlings emerge allow them to grow for two years before transplanting them in the autumn.

Requirements and care: is so variable Full sunlight; some species in partial shade. pH 5.5 to 8.0 (species dependent). Dry or wet soil (species dependent). Provide a low nitrogen spring feed. Regular watering during dry periods. Deadhead. Provide support for taller species. Propagate: by dividing rhizomes once flowering has finished; or by division of bulbs in the autumn.
Miscellaneous: As members of this genus require different growing conditions and care it is recommended to buy a specialized Iris growing book. The name Iris comes from the Greek word for Rainbow. Flowers have evolved to be especially attractive to insects. Rhizomes often used in perfumery.

How to Grow Iris

It is easiest to grow Iris from purchased bulbs or rhizomes. The depth that the bulb should be buried is dependent upon species, but in the range of 5 to 12 cm (2 to 5 inches).

When planting Iris bulbs best results are obtained by planting in the early months of autumn. If you are growing from rhizomes then these should be planted level with the soil surface in the spring.

It is difficult to grow Iris from seeds but if you intend to do so, first soak the Iris seeds for a full day in warm water. Then sow into flats in the spring, place the flats in a black plastic bin bag, then place carefully in the fridge for three weeks.

The flat should then be sunk into the ground in a shady area of the garden and covered with glass.

It can take anything from one month to one and a half years for the Iris sees to germinate, so be prepared to be patient, and keep an eye on the flat to keep it moist.

Once seedlings emerge allow them to grow for two years, before moving to their final location in the garden.

Caring for Iris in the Garden

There is a little minor work involved in looking after Iris once they are growing in the garden.

They should be fed in the spring (low nitrogen fertilizer); watered during prolonged dry spells of summer; staked; and deadheaded following flowering.

If you require more Iris plants then they can be propagated by division of the bulbs (autumn) or rhizomes (once flowering has completed).

Common Questions

How many members does the Iris plant genus contain?

The Iris genus is quite large with about 300 species. These plants range from small dwarf Irises to tall, large-flowered varieties.

Do members of Iris make a good garden or landscaping plant?

Yes, Iris plants make stunning garden plants. Their vibrant flowers and decorative foliage provide a striking visual element in any garden or landscape.

Which Iris species are most frequently grown by gardeners?

Species such as Iris germanica (German Iris) and Iris sibirica (Siberian Iris) are popular in gardens as they have beautiful bold blooms.

Are members of the Iris plant genus fragrant?

Yes, many Iris species are fragrant. The aroma varies by species, with some smelling sweet, floral, or even like vanilla.

What is the perfect location to grow Iris?

Iris prefers a location with full sun to partial shade and well-drained soil. It is also advisable to give them plenty of space to flourish.

Is Iris invasive in the USA, if so in which states?

Some Iris species can become invasive under the right conditions. For instance, Yellow Iris (Iris pseudacorus) is invasive in certain parts of the USA.

How do I remove Iris plants from my garden?

To remove Iris, dig up the entire plant, ensuring to remove the rhizomes to prevent regrowth. Dispose of the plant parts responsibly.

Summary

The Iris genus belongs to the Iridaceae family, comprises perennial plants native to temperate regions of the Northern Hemisphere. Recognized for their striking, often multicolored flowers, Irises are a staple in many gardens.

Iris plants prefer full sun to partial shade, and a well-drained soil. Regular watering is required, but overwatering should be avoided. Propagation is generally done through division, usually in late summer after blooming.

I hope that you enjoyed this guide on how to grow Iris plants. You may also enjoy my gardening guides on how to grow Lapeirousia, Lobelia plant, and Anoda plants.