May is the perfect month to fill your garden with flowers that will bloom all summer long.
The risk of frost is nearly behind us, the soil is warming up, and there’s no better time to get planting for a vibrant, colourful display right through until autumn.
Whether you’re refreshing borders, filling pots, or creating a brand-new bed, here are the best summer flowers to plant in May for maximum colour and impact.
1. Petunias – The Summer Staple
Petunias are one of the best-loved bedding plants for good reason. Their big, bold blooms come in every colour imaginable, from pure white to deep purple and electric pink.
✅ Why We Love Them:
- Long flowering season from May to the first frosts.
- Perfect for hanging baskets, pots, and borders.
- Easy to grow and low maintenance.
🌿 Tip: Deadhead regularly to keep them flowering at their best.
2. Geraniums (Pelargoniums) – Drought-Tolerant Favourites
Geraniums are brilliant for adding bold splashes of colour and thrive in sunny, dry conditions. They’re ideal for busy gardeners because they’re incredibly forgiving.
✅ Why We Love Them:
- Available in reds, pinks, whites, and purples.
- Great for containers and window boxes.
- Drought-resistant once established.
🌿 Tip: Water at the base to avoid leaf spotting and feed every couple of weeks with a liquid fertiliser.
3. Cosmos – Airy, Elegant Blooms
Cosmos produce delicate daisy-like flowers above feathery foliage, adding movement and elegance to beds and borders.
✅ Why We Love Them:
- Bloom profusely from midsummer to autumn.
- Excellent for cutting gardens — they look beautiful in vases.
- Easy to grow from seed or small plug plants.
🌿 Tip: Pinch out growing tips when young to encourage bushier plants.
4. Marigolds – Sunny and Cheerful
Marigolds are tough, reliable, and fantastic for adding bright yellow, orange, and red tones to your summer displays.
✅ Why We Love Them:
- Natural pest deterrents – they repel aphids and other nasties.
- Bloom quickly and last well into autumn.
- Suitable for flower beds, veggie plots (companion planting), and pots.
🌿 Tip: French marigolds are compact and great for edging, while African marigolds grow taller and make a bold statement.
5. Dahlias – Drama and Impact
For show-stopping blooms in bold colours and extravagant forms, you can’t beat dahlias. Plant dahlia tubers in May for flowers from mid to late summer onwards.
✅ Why We Love Them:
- Huge variety of colours, sizes, and flower shapes.
- Amazing for borders and cut flowers.
- A real statement piece for any garden.
🌿 Tip: Stake tall varieties when planting to avoid snapping stems later in the season.
6. Begonias – Shade-Loving Superstars
If you have shadier spots, begonias are your go-to flowering plant. They thrive in partial shade and offer vibrant colour where sun-lovers won’t flourish.
✅ Why We Love Them:
- Long flowering period from May to October.
- Happy in pots, baskets, and shady borders.
- Available in upright or trailing varieties.
🌿 Tip: Water begonias carefully—too much moisture can cause rot, especially in cooler spells.
7. Zinnias – Bold and Easy Growers
Zinnias are fast-growing annuals that produce bright, cheerful blooms in vivid reds, pinks, oranges, and yellows. They love the heat and reward you with colour all summer.
✅ Why We Love Them:
- Very easy to grow from seed.
- Tolerate heat and drought once established.
- Brilliant for pollinators, attracting bees and butterflies.
🌿 Tip: Zinnias don’t like cold nights, so only plant outside once all risk of frost has passed.
Quick Summary: Top Flowers to Plant in May
| Flower | Key Features |
|---|---|
| Petunias | Colourful, long-blooming, perfect for containers |
| Geraniums | Drought-tolerant, great for sunny spots |
| Cosmos | Elegant, airy, loved by pollinators |
| Marigolds | Bright, hardy, pest-repelling |
| Dahlias | Dramatic, perfect for cutting |
| Begonias | Ideal for shady spots |
| Zinnias | Fast-growing, heat-loving |
May Planting Tips for Summer Colour
✅ Harden off indoor-grown plants before planting them outdoors.
✅ Mix annuals and perennials for continuous colour and structure.
✅ Feed plants regularly once established with a high-potash fertiliser to encourage blooming.
✅ Water well after planting, especially on dry days.
✅ Mulch around plants to retain moisture and reduce weeds.
Conclusion: A Garden Full of Colour Awaits!
Planting in May is all about bold colours, long blooms, and easy care. With these gorgeous flowers, you’ll be on your way to creating a dazzling garden display that will keep you smiling all summer long.
Need Help Planting Your Summer Garden?
At Project Garden, we offer expert planting, garden makeovers, seasonal displays, and maintenance services to bring your dream garden to life.
📞 Call 07795 800 772
📧 Email info@projectgarden.co.uk
Let’s fill your garden with summer colour!