When to plant iris bulbs – for a colorful and showy display

Work out when to plant iris bulbs and you can enjoy these sensational flowers from early spring through to summer. With distinctive, elegant petals and exquisite markings they never cease to impress. 

Choose from early flowering varieties with their dainty flowers and delicate fragrance or opt for one of the many taller European types such as Dutch, English and Spanish that come into their own midsummer. These tend to come in a wider range of colors and have larger long-lasting blooms set against dark green sword-like foliage. 

You can grow irises happily in free draining soil and love to flower in a sunny spot, but some will tolerate part shade too. Long lived and pretty hardy – thriving in USDA hardiness zones 3-9 – they will last for several years with very little care and attention. Not to be confused with rhizome irises, bulbous types need an annual cold dormant period to build up energy stores ready to bloom again the following year. 

When to plant iris bulbs

Depending on whether you want petite early flowerers or larger midsummer blooms, this spring bulb guide is laden with expert tips, will help you know when to plant iris bulbs with confidence.

When to plant spring flowering iris

‘Iris bulbs must be planted in the fall because they require a long period of cold temperatures in order to set their flower buds,’ advises Venelin Dimitrov, Product Manager at Burpee. Plant bulbs in fall as soon as possible after receiving or buying your bulbs.

Dimitrov also says to, ‘Select a site in full sun to light shade with good drainage where water does not stand on the surface after a rain event. Bulbs thrive in well-drained, moist soils. Mulch the soil to protect the bulbs from the heat of strong summer sun.’

Smaller spring flowering iris such as Iris reticulata and Iris danfordiae will fill your yard with color and fragrance during February and March, when very little else is in flower. Stunning planted in clumps and naturalized in grass, under deciduous trees, they can create carpets of blue, white and yellow with very little effort. Their open, graceful blooms – with a trio of upright petals set amongst three drooping ‘falls’ or longer petals – are a highly valuable and popular food source for early emerging pollinators. 

When is the best time to plant summer flowering iris bulbs?

Irises are also amongst the best summer bulbs, too. Again, it's important to plant bulbs in fall well before the first frosts.

‘Dutch irises, like bearded irises, grow from bulbs and require a cold period to bloom,’ says Annette Coppess at Breck’s. ‘Try planting these smaller bulbs in early fall – after the weather cools but before the soil becomes extremely cold. These bulbs will need cooler, but not freezing, temperatures to settle into their new home before winter.’ 

Growing to around 20-23 inches (50-60cm) high, these large showy blooms look fantastic growing outside in borders and pots and make brilliant cut flowers too. With colorful blooms in a huge array of striking and unusual shades – including azure blue, white flushed with lime and blush pink to copper, each flashed with a golden eye – they are surprisingly good natured and demand very little attention.

When to plant iris in pots and planters?

As with all bulbous iris, these are best planted in fall, as they require a cold period to prompt them into growth. If you fancy growing these reliable backyard beauties in pots and planters do bear in mind that some types of iris are more suitable than others. 

Paul Blom from specialists Bloms Bulbs says, ‘The lovely Dwarf Iris are among the earliest of the spring bulbs and provide the richest colors and are particularly suitable for the rock garden or pots and small containers. Whereas the Dutch, English and Herbaceous types feel more at home in the border.’

Thanks to their early flowering period and small bulb size, dwarf iris are ideal candidates for layering with other spring flowering bulbs. Known as a ‘bulb lasagne’ it is a popular and easy way to plant up a single container and ensure a succession of blooms that will last for weeks.