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7 container flowers to plant in May for non-stop colour all summer long

Pick these vibrant, long-lasting blooms to ensure a colourful display that will see your garden all through the summer months

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pink petunias in container
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As things start to heat up outside, it can be hard to resist diving in and filling up the patio with row upon row of colourful pots and planters. But rather than relying on impulse buys that may fade quickly, choose wisely, and there are plenty of fabulous container flowers that can be planted in May to give non-stop colour all summer long.

May is the perfect time to get started when it comes to planting up containers - the weather is warmer and the risk of overnight frosts fading - so filling pots and planters now with long-lasting blooms leaves one less thing to think about when it comes to garden jobs for May.

‘While your borders may already be thriving, container gardening shouldn’t be overlooked,’ says Shelley Davis, flower expert at Flying Flowers. ‘Planting summer flowers in various pots and containers offers great flexibility, making it ideal for small spaces like patios and balconies while allowing for precise control over soil quality and sunlight exposure. And by selecting a diverse mix of heat-loving plants, you can create a dynamic display of textures and shades that will remain vibrant all summer long.’

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1. Petunias

pink petunias in container

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‘Petunias are the gold standard for May container planting because they thrive in the warming soil and provide a relentless blooming cycle that lasts until the first autumn frost,’ advises Shelley. ‘Their diverse growth habits, ranging from cascading trailers like these Petunia Surfinia Purple Basket Plants, £17.99 from Gardener's Dream to dense mounds, allow them to fill pots quickly with vibrant, high-impact colour.’

‘Unlike more delicate varieties, low-maintenance petunias are incredibly resilient and “heavy bloomers”, meaning that with regular watering and deadheading plus occasional feeding, they will remain lush long after other plants have peaked.’

‘With any container, success starts with choosing the right size, so select a pot one to two inches wider than the original nursery container, or, if sowing seeds, evenly place each seed just below the soil surface,’ suggests Shelley. ‘Most importantly, ensure proper drainage by using pots with base holes and adding a bottom layer of stones before filling with soil to prevent waterlogging.’

Where to buy petunias:

2. Begonias

Pink begonia flowers growing in garden

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With masses of long-lasting, super-bright flowers, begonias are a great choice for pots, window boxes and hanging baskets, flowering pretty much non-stop between July and October. While begonias do best out of direct sunlight, position them in a shady spot or north-facing garden, and begonias are hard to beat.

When it comes to when to plant begonia tubers, there is some flexibility. While they can be started indoors around March to April, the tubers are vulnerable to frost, so waiting until May before planting begonias outside in pots can be a better bet.

Where to buy begonias:

3. Geraniums

red geraniums in container

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‘Geraniums are another summer staple because of their exceptional drought tolerance and sturdy, long-lasting flower heads that thrive in the summer heat,’ says Shelley. ‘These sun-loving plants are incredibly resilient, making them ideal for gardeners who want high-impact colour with minimal maintenance.’

‘And because geraniums bloom continuously through the seasons, they provide a reliable architectural focal point in pots, offering both vibrant clusters of flowers and attractive, fragrant foliage that keep containers looking full and healthy.’ This Trailing Balcony Geranium 'Decora' Collection, from £12.99 at Gardening Direct, will add plenty of interest.

Where to buy geraniums:

4. Cosmos

cosmos in container

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Avid bloomers that produce masses of flowers all summer long, cosmos are super-pretty and perfect for lovers of cottage garden or prairie-style planting schemes. While often grown in flower beds and borders (reaching up to 1m in height), cosmos can be a good choice for containers too. However, shorter varieties are recommended, such as these Cosmos Sonata mixed, £12.99, Gardening Direct (which are closer to 30cm in height), so easier to grow in pots.

Wait until mid to late May, when the danger of late frosts has passed, before planting out cosmos. Choose a deep, wide-based pot as cosmos can become top-heavy, making sure it is fairly weighty so there’s less chance of it toppling over as the plant grows taller. And drainage holes are a must too, to ensure the plants don’t get waterlogged.

Where to buy cosmos:

5. Calibrachoa

orange calibrachoa in container

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‘Calibrachoa, often called million bells, is an essential May addition to the garden due to its incredible flower density and self-cleaning nature, which eliminates the need for deadheading,’ says Shelley.

‘While calibrachoa resemble miniature petunias, these plants are significantly more resistant to pests and disease, and one of the best trailing plants for containers, maintaining a lush, cascading carpet of blooms that spill over the edges of pots and hanging baskets.’ These Calibrachoa Million Bells Super MixMillion Bells, from £9.99 at J.Parker's, will create the most eye-catching of displays.

Keep calibrachoa plants well watered, especially in very hot weather, but ensure that excess water can drain away as calibrachoas don’t like sitting in waterlogged soil - use pot feet under containers to aid drainage.

Where to buy calibrachoa:

6. Dahlias

Dahlia 'dreamy Nights'

(Image credit: Sarah Raven)

As it gets warmer towards the end of May, dahlias are a safe bet for providing non-stop summer colour, giving big, bold blooms right up until the first frosts in autumn.

To grow dahlias in pots, either plant up dahlia tubers that you have been keeping undercover inside or buy young plants from the garden centre. Choice of pot is key; it should be at least 12 inches deep (and roughly the same wide) to ensure it won’t topple as dahlias put on a lot of top growth. It’s also worth staking dahlias to support them as they get bigger.

Choose a sunny spot on your patio or balcony, as dahlias are sun-loving plants and need plenty of sunlight each day to thrive. And remember to deadhead dahlias regularly to remove the faded blooms, which will help to keep the plant flowering for longer.

For pots in particular, opt for dwarf varieties of dahlia, like these Dahlia Figaro Dwarf White Shades, £3.99 from Gardening Express, that stay quite compact and are better suited to container gardening, unlike taller varieties that can often reach 5ft tall.

Where to buy dahlias:

7. Marigolds

marigolds in container

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‘Marigolds are an excellent choice for May containers because of their ability to produce fiery blooms in even the most intense summer heat,’ suggests Shelley. ‘These hardy annuals are exceptionally easy and a fast-growing flower to try, offering a compact, bushy show that fills pots with shades of gold, copper, and orange.’ I have my eye on these huge pom-pom-headed Marigold 'Marvel Mix', from £14.99 at Thompson & Morgan.

‘But beyond their visual appeal, marigolds are also highly valued for their pest-repellent properties and their no-fuss nature, as they are notably drought-tolerant and can thrive in various soil conditions. Whether used as a vibrant border in a mixed planter or as a standalone splash of colour, marigolds provide a reliable, low-maintenance display that stays bright and healthy all season long.’

Where to buy marigolds:

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Is your patio lacking colour? What flowers will you be planting up for summer... let us know.

Lisa Fazzani
Lisa Fazzani
Freelance content editor

Lisa is a freelance journalist who has written about interiors for more than 25 years. Previously editor of Style at Home magazine, she has worked on all the major homes titles, including Ideal Home, Country Homes & Interiors, 25 Beautiful Homes and Homes & Gardens. She has covered pretty much every area of the home, from shopping and decorating, crafts and DIY to real homes and makeovers and now regularly writes gardening stories for Ideal Home.