When to plant summer bulbs - experts reveal the perfect time to ensure your garden is filled with colour

 Alitex antique set of drawers with dahlias in vases above in greenhouse.
Alitex antique set of drawers with dahlias in vases above in greenhouse.

As we move towards spring, you may have wondered when to plant summer bulbs this year. And what we mean by summer bulbs are bulbs that grow and flower over the year's warmer months. So, May through to September and sometimes into October, depending on the temperatures.

If you already know when to plant spring bulbs, summer bulbs are usually planted a little later in the year when it's warmer.

‘Summer bulbs bring vibrant colours and unique shapes to our gardens, making them a popular choice among horticulture enthusiasts,’ Tim Marshall, Raby Castle’s Head Gardener, outlines. From pretty dahlias and lilies to bright begonias, they can instantly lift the look of any garden design.

‘However, to ensure a successful growing and blooming period, it is crucial to plant them at the right time and in the right location,’ Tim continues. But when should you get started?

We've asked the experts when is the best time to plant summer bulbs, as well as the best summer bulbs to plant and fill your garden border ideas with beautiful and bright blooms all summer long.

When to plant summer bulbs

If you want guaranteed blooms for summer, experts recommend planting them between March and May, with May often being the optimum month. So, it might be time to start considering which types of summer bulbs you want to plant this year.

Bulbs planted in terracotta pots
Bulbs planted in terracotta pots

However, It is important to wait until the last frost of the season has passed – which can be tricky given the unpredictable weather that we have here in the UK. If the weather or temperature is too cold, when you plant summer bulbs, they could struggle to establish themselves or become damaged by frost.

‘Most summer bulbs need temperatures of 13 degrees and above to grow, so you’ll want to wait until the temperature is consistently above this before planting,’ warns Craig Wilson, Co-founder, Director and Gardening Expert at Gardeners Dream. ‘However, there are some more hardy types, such as lilies, that can be planted slightly earlier as they are less sensitive to frost and chillier temperatures.’

On the other hand, you don’t wait too long to get planting and miss out on the chance to have your bulbs bloom in time for summer.

White cala lillies in garden
White cala lillies in garden

‘Any later than April and you’re running the risk that your bulbs won’t have time to establish and you may miss the chance to have a beautiful display of blooms in the summer,’ Jamie Shipley, Gardening Expert and Managing Director of Hedges Direct, warns. So, it’s all about getting this timing just right.

‘Summer bulbs generally should be planted anywhere between late spring and early summer, usually around late April and early June time,’ says Steve Chilton, Garden Expert at LeisureBench. ‘This allows them to fully establish their roots before the warmer weather arrives, which is important for their health and growth development.’

Essentially, you’re looking for the ground and soil to be warm but not too hot and for the risk of frost to be at its lowest when you go to plant summer bulbs.

The best summer bulbs to plant

Depending on your preference, there are a number of beautiful summer blooms that you can get planting this spring. But the experts agree on several that all work well in UK gardens whether you are looking to fill container garden ideas or add colour to small garden ideas.

  • Dahlias

  • Lilies

  • Begonias

  • Gladioli

  • Crocosmia

‘For flower beds, Dahlias, Gladioli and Crocosmia are great for structure,’ suggests J Parker's Gardening Expert, Hannah Rowson. While ‘shorter plants like begonias and compact Dahlias or Lilies work great for containers.’

‘Gladiolus are typically planted in late spring (April to May). Whereas Lilies and begonias can be planted from late spring to early summer (May to June),’ Tim affirms.

Pink Gladiolus
Pink Gladiolus

It is, however, important to ‘choose bulbs that suit your garden's conditions and your personal aesthetic preferences,’ admits Josh Novell, Director of Polhill. ‘Consider the height, colour, and blooming time to create a well-balanced and visually appealing garden.’


Where is best to plant summer bulbs?

Whether you have a sprawling garden or a smaller amount of space to work with, there are a few key considerations to make before planting bulbs.

‘When selecting a planting location, keep in mind that most summer bulbs thrive in well-drained soil with full sun exposure,’ Tim explains. There are always a few exceptions to the rule. For example, ‘begonias prefer partial shade,’ Tim affirms. So, it can be worthwhile taking a note of the specific requirements for each bulb variety and then choosing an appropriate area in your garden, depending on this.

‘The likes of raised beds, borders, and even containers are suitable for summer bulbs, as long as the location has enough sun and the soil is right,’ says Steve. ‘I also recommend planting them in locations that receive at least 6 hours of direct sunlight per day.’

Red begonias growing in a stone urn
Red begonias growing in a stone urn

Should I plant summer bulbs in the ground or containers?

Again, this will depend on what kind of outdoor space you have available to you. But if you only have a patio, balcony or small garden, many summer bulbs can flourish in containers. ‘Planting in containers can be more practical for those with less available space or if the soil conditions in the ground aren't necessarily perfect, as they allow you to be able to control it more,’ Steve concludes.

If planting in pots or containers, 'just make sure to raise them off the ground with pot feet to avoid waterlogging and deter slugs,' Antony Flooks, Online Store Manager at Hillier Garden Centres, advises.

Whether they are planted in the ground or in containers, the ideal time for planting summer bulbs will still be around the same.

When do summer bulbs typically flower?

Generally, summer bulbs typically start flowering from mid-summer onwards, the experts agree. But ‘the exact flowering time can vary depending on the specific bulb type,’ Steve remarks. For example, ‘some varieties, like Dahlias, have long flowering times so can flower from summer into autumn,’ says Hannah.

So, you can enjoy a variety of colourful blooms all summer long, if you plant your bulbs at the right time.

How can I plant summer bulbs when there may be future frosts?

Even when you think spring has well and truly sprung, the great British weather can surprise us all with some unexpected frost in March and April. But how can you go about preparing for this? Well, Jamie has a few tips.

‘If we do experience any March frost, planting in a sunny part of your garden will mean the soil can recover more quickly, diminishing the damage a cold snap will have on your bulbs,’ he affirms. And if you’d like to get your summer bulbs planted in early spring, when frost and cold temperatures could still be on the cards, ‘a heated greenhouse or indoor windowsill are ideal environments for the bulbs to begin their establishment protected from the cold,’ Jamie concludes.