When to plant summer bulbs – prepare for a show-stopping display with these timing tips

Get set for a spectacular show by planting dahlias, crocosmia, gladiolus and more at the right time

(Image credit: iBulb)

When winter comes to an end, the spotlight shines on spring bulbs. These are the tulips, daffodils, and hyacinths that fill our gardens with color after being planted with anticipation back in the fall. But while enjoying the cheery spectacle, it pays to think ahead once again, and start planning our summer garden show.

Summer bulbs – such as dahlias, begonias, agapanthus and gladioli – provide some of the most beautiful blooms when temperatures soar. And, growing them from bulbs is easy and generally cheaper than buying ready-grown potted plants from garden centers. But it's important to plant your summer bulbs at the right time.

‘It’s best to note that summer bulbs are not tolerant of cold temperatures, so they should only be planted when the ground is warm,’ says Aya Bradley, a gardening expert at The Golden. This is why, in many regions, it's best to lift and store them for winter, or at least protect them with a layer of mulch. Spring is the time to plant them – but are there more precise timings you should follow? This guide explains all you need to know for the best chance of success. 

Holly Crossley
Holly Crossley

A former professional gardener and allotment-grower, Holly now spends her days writing about plants and outdoor living for Homes and Gardens, caring for her large collection of houseplants, and drawing her favorite blooms.


Crocosmia brings hot hues to a flower bed

(Image credit: iBulb)

When is the best time to plant summer bulbs outside?

Generally, the temperature of the soil should be consistently over 50˚F and the risks of frost long gone for planting summer bulbs outdoors. This means the exact time will vary slightly depending on your hardiness zone: in hotter climates, you can plant them earlier in the season, while in cooler regions, you may need to wait until May.


Agapanthus are a favorite for summer pots

(Image credit: iBulb)

Can you start summer bulbs off indoors?

Many gardeners choose to start their tender and half-hardy summer bulbs, such as dahlias, gladiolus and begonias, indoors. An ideal place would be a frost-free greenhouse. Doing so in February, March or April will give them a good head start before the soil has warmed up enough to plant them outdoors.

When you do go to plant these types of summer bulbs outside, harden them off first to acclimatize them to outdoor conditions. This means putting the pots in a sheltered space outdoors during the day (and bringing them indoors at night) for a week or so before planting them in their final position.

When planting bulbs, providing good drainage is key, and fertility is important, too, if they are destined to stay in the spot for a long while. 

'Once the flowers have died back, always remember to leave stems and foliage to die back naturally to ensure that the bulbs swell to a good flowering size for the following year,' says John Negus, a garden expert from Amateur Gardening.

John Negus
John Negus

John has been a garden journalist for over 50 years and regularly answers readers' questions in Amateur Gardening magazine. He has also written four books and has delivered many talks over the years on horticulture.


Gladioli can be started off in a greenhouse

(Image credit: John Richmond / Alamy Stock Photo)


What happens if you plant summer bulbs too late or too early?

Summer bulbs shouldn’t be planted too early in the year, or they could be damaged by frost before they have a chance to grow. Too late, however, and they will fail to thrive in the summer. June is the latest you should plant them.

Should you plant alliums at the same time as other summer bulbs?

Alliums' blooming time is on the border between late spring and early summer. They are usually treated as spring bulbs and planted in the fall. Planting the bulbs in the spring can reduce their flowering potential, but they should put on a beautiful show over the following years.

It's easy to get distracted by the beauty of spring bulbs – but, as is often the case with gardening, don't be tempted to rest on your laurels. If you want your garden to continue looking glorious for the upcoming months, start planning and planting your summer bulbs now – you'll be enjoying their fabulous flowers before you know it.

Holly Crossley
Contributing Editor

The garden was always a big part of Holly's life growing up, as was the surrounding New Forest where she lived. Her appreciation for the great outdoors has only grown since then; over the years, she's been an allotment keeper, a professional gardener, and a botanical illustrator. Having worked for Gardeningetc.com for two years, Holly now regularly writes about plants and outdoor living for Homes & Gardens.

With contributions from