Irises: Bearded, Beardless and Beyond

Whether your taste leans towards the enchantment of frilly bearded irises or steers towards the sleek, contemporary allure of Dutch irises, one thing remains certain: they'll infuse your garden with unparalleled beauty in vibrant hues, and steal the show. 

With a flourishing genus boasting over 325 recognised species and more than 50,000 named varieties, these floral gems boast some of the most dazzling blooms in the garden.

You might recognise some familiar names such as bearded iris, Dutch iris and Louisiana, but what sets them apart from one another? Let's dive into the delightful world of irises and unearth their secrets. 

Understanding the Differences Between Irises

Irises come in two main forms: rhizomes and true bulbs. The rhizomatic types flaunt larger flowers and include both bearded and beardless varieties. Bearded irises, native to central and southern Europe and the Mediterranean, sport thick, bushy 'beards' on each of their lower petals. Meanwhile, their beardless cousins, Japanese, Spuria, Siberia and Louisiana, prefer a ‘clean-shaven’ look. On the other hand Iris japonica, also grown from rhizomes, offers more frills than fuzz. Dietes, an indigenous wild iris, adds to the diversity of rhizomatic types. It is the Dutch iris, though, that stands out as the rebel of the group, being the only true bulb among them.

Bearded iris

Arguably the most renowned among gardeners, bearded irises (I. germanica) are believed to have emerged from the interbreeding of approximately fourteen wild iris species. As variations in size proliferated through breeding, bearded irises have been categorised into six distinct groups based on plant size and growth habit. Bursting into a spectacular display in spring and early summer, they span almost every hue of the rainbow and beyond, earning them the nickname 'rainbow flower'. Deep purples, blues, and near-black shades further distinguish them from other flowering plants. Their cultivation is a breeze—simply find a well-draining spot in full sun, and plant with the rhizome's top half just above the soil, water regularly and voilà! You have a plant that is set to thrive. Remarkably pest-resistant and requiring minimal maintenance, they return year after year.

Optimal planting time is from October to December in South Africa, or wait until cooler weather from mid-April to late May when irises enter a semi-dormant state. 

Dutch iris

Contrary to their name, Dutch irises (I. x hollandica) hail not from Holland but originally from sunny Spain. However, hybridisation was achieved in Holland. These dramatic spring-flowering bulbs boast orchid-like flowers and silky petals. They thrive in dappled shade to full sun, provided the soil is well-draining. When you plant them, cover the bulbs with 5cm of soil. Reaching heights of about 50cm, these ‘tallies’ are unsuitable for the front of garden beds or before low-growing plants. Most gardeners treat them as annuals, replanting fresh bulbs each autumn. Just ensure you incorporate compost at planting time and use it as a mulch too, to help regulate the soil temperature. 

Louisiana iris

Louisiana irises flourish in diverse conditions and boast an extensive colour range. This water-loving iris is an evergreen, spring-flowering perennial with sword-like leaves. They are ideal for pond margins or well-watered garden beds in full sun, but some afternoon shade can be provided in hot summer growing conditions. These water babies aren’t keen to get scorched. The wetter the soil, the more vigorous the growth, so deep watering is best. These spring flowering sensations grow well in up to 15cm of standing water. They are also tolerant of clay soils which retain moisture. Avoid well-drained sandy soils unless copious amounts of organic matter are added. Soils should never dry out during the growing season. They can be grown in pots sunk into the ground in water gardens. Otherwise, they can also be grown in elevated beds as long as adequate moisture levels are maintained. Plant the rhizomes at least 3cm deep to prevent bacterial rot. Just watch out for unwanted guests (snails and slugs love irises just as much as you do). 

Divide clumps every 3-4 years if overgrown, but avoid disturbing them during hot weather. Opt for low-nitrogen fertilisers, which will help prevent iris rust, which is caused by excessive nitrogen levels. 

Iris japonica

In early spring, gardeners are captivated by the ethereal beauty of Iris japonica, particularly the crested Iris japonica with its ruffled white blooms. Flourishing in shady garden corners, these evergreens multiply rapidly in slightly acidic soil through surface-rooting rhizomes. While they tolerate dry conditions, this ‘tough guy’ can do with occasional and deep watering. 

Siberian, Spuria and Japanese irises

These vigorous growers show off their blooms anytime from late spring to mid-summer and can be planted in either autumn or spring. Keep them moist and plant them in rich acidic soil, around 45cm apart, in full sun. Don’t cut these varieties back, just remove dead leaves and flowers or when you see small pointed green shoots appearing.

Dietes (wild irises; butterfly iris)

Dietes varieties, including the large wild iris (D. grandiflora) and the yellow version (D. bicolor), are evergreen perennials prized for their Forest Gump-like resilience. Come drought, frost or continuous rain, the butterfly iris remains unfazed. Plant in full sun or partial shade for best results. These local stars reach heights of up to 1m. Space them 40cm apart, and cover the rhizomes with 2cm of soil. 

No matter the variety you’re planting out, apply a layer of compost as mulch to help regulate the soil temperature. Then, for those who may have heavy or clay soil – add compost and gypsum to improve drainage.

Regardless of your preference, irises offer a full spectrum of colours to enhance any garden design, bringing joy to your landscape. Happy gardening! 

Caution: none of these bulbs are for consumption – they can be harmful if eaten by humans or animals – so please do exercise caution when there are children and pets around them.