7 of the best annual flowers to plant in May for bountiful, dazzling blooms to fill borders and pots

If you dream of your flower borders and containers filled with glorious color this summer, May is a fantastic month to sow annual flower seeds. Many easy-to-grow flowers producing blooms of different colors, sizes, and shapes can be sown this month.

I have picked seven of my favorite annual flowers to plant in May. These selections can give drama in flower beds, attract pollinators to a space, and be cut for vases to display in the home.

The likes of calendula, bachelor's buttons, cosmos, strawflower, sunflower, and more can be started from seed this month. They are all annual flowers I have grown from seed as a professional gardener for many years, and I provide tips for sowing and maintaining plants.

Flowers to plant in May - our top picks

Whether you want bright blooms for flower beds or easy-to-grow flowers for container gardens, the following are a selection of some of the best annual flowers to plant in May that can bring dazzling color to any space.

1. Amaranthus

Amaranthus, known as love lies bleeding, is a unique and stunning ornamental annual. Growing up to 4-6 feet tall, depending on the variety, amaranthus produces distinctive cascading blooms, predominantly in shades of purple or light pink, that add guaranteed drama to any space.

Amaranthus is an easy annual to grow in spring. The flowers can be started indoors earlier in the year or sown directly into the garden in May, once the risk of frost has passed and the temperatures reach 60-65°F.

Sow seeds outdoors where the amaranthus is to flower and cover with a thin layer of soil. Keep the seeds well-watered and amarathus will germinate within 7-10 days. Thin the seeds as they appear to at least 12 inches apart, and the annual plant should flower around 12 weeks after sowing and last until the first frosts.

2. Calendula

Calendulas, also known as pot marigold, are beautiful and multi-purpose plants. Not only do they look great, but calendula is a great plant for pollinators and a source of edible flowers. Different calendula varieties come in bright tones of orange, yellow, or white, while bi-colored varieties can also suit many different tastes.

These fast-growing flowering annuals are easy to grow from seed directly into a sunny spot in the garden. Simply press the curvy calendula seeds into the soil and cover them lightly, as they need light to germinate. Keep them moist, and they should germinate within two weeks.

Calendula will flower profusely through summer. Deadhead plants for a long display, or harvest calendula seeds to sow again next year.

See the range of calendula flower seeds at Amazon

See the range of calendula flower seeds at Walmart

See the range of calendula flower seeds at True Leaf Market

3. Cornflower

Cornflower, or bachelor’s button, is a delicate flower very popular as part of cottage gardens and wildflower gardens. The blooms come in many colors and, despite being small, can make fantastic cut flowers thanks to their long vase life. Best known for their blue flowers, bachelor’s button varieties can also be pink, white, and dark red.

The annual flowers can be sown directly into their growing position this month. Cover them only lightly with soil, keep the soil consistently moist, and the seeds should germinate within two weeks at temperatures of 60-70°F. So reliable is cornflower at germinating that it makes a great plant for chaos gardening, to just scatter around the garden.

4. Cosmos

Growing cosmos is super-simple, and the reward is lots of gorgeous flowers in bright, vivid shades complemented by the plant’s soft foliage. Keep the cosmos blooming by deadheading, and you can get a spectacular display through summer and into fall.

While you can plant cosmos seeds indoors in spring to get earlier flowers, May is a time to sow seeds directly into their growing position. Pick a full sun position and rake the ground to a fine consistency, before sowing the seeds 2-3 inches apart and keeping the soil moist.

Thin seeds to around 12 inches to give plants space to develop. It is also good practice to pinch the tips of all types of cosmos when the plants reach around 12 inches, as this can give you longer stems and more flowers.

See the range of cosmos seeds at Amazon

See the range of cosmos seeds at Walmart

See the range of cosmos seeds at Burpee

See the range of cosmos seeds at True Leaf Market

5. Nasturtium

There are many reasons to grow nasturtiums. They are one of the easiest flowers to grow from seed, their bright blooms come in a variety of colors, the flowers and leaves are edible, plus they are great for companion planting.

Once the risk of frosts has passed for your climate and the soil warms to 55-65°F in spring, you can plant nasturtium seeds directly into the soil. The seeds want to be planted at just under an inch deep and at a minimum of six inches apart.

Keep the soil moist and thin the seedlings to 12 inches apart when they appear. You can get nasturtiums that produce flowers of one color, though I prefer a mix such as this Nasturtium ‘Alaska Mix’ at Burpee that produces blooms in multiple bright shades.

6. Strawflower

Strawflower, or Helichrysum, is a great plant for a cut flower garden and a must for anyone passionate about dried flowers. Also known as everlasting flowers, the blooms are delicate and come in different colors, sitting on top of tall stems.

When picked as cut flowers, they have a long vase life and if you dry strawflowers, the blooms can be used in wreaths, garlands, or more to decorate with dried flowers.

Where you sow the flower in May depends on your climate. It is best to sow seeds indoors 3-4 weeks before the last frosts in colder areas, while warmer climates can sow outdoors after the frosts have passed.

The seeds want to be pressed onto the surface of compost or soil and kept moist for good germination. Space the plants at least 12 inches apart and support the stems if you live in a windy area.

7. Sunflower

Bright, cheery, ever-popular with people and pollinators, it is no shock that growing sunflowers is on many gardeners’ to-do lists every year. And they are simple flowers to grow from seed that come in a wide range of colors and sizes.

Most people will picture the classic yellow sunflower, but there are sunflower varieties in shades of red and orange - some are even bicolor.

You can plant sunflower seeds indoors or outdoors in May. Either sow the seeds into individual large pots to start indoors and plant out next month, or pop them directly into the soil around an inch deep.

When sowing outdoors, space seeds at least six inches apart and thin to around 18 inches when the seedlings appear.

See the range of sunflower seeds to plant at Amazon

See the range of sunflower seeds to plant at Walmart

See the range of sunflower seeds to plant at Burpee

See the range of sunflower seeds to plant at True Leaf Market

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FAQs

Can I sow wildflower seeds in May?

May is not an ideal month to plant wildflower seeds. March or April are preferable months to sow seeds in a wildflower garden or plant a wildflower meadow. If you missed that window, it is better to wait until fall for more favorable conditions.

As well as knowing what annual flowers to plant in May to fill beds and pots with blooms, our guide to the best vegetables to sow in May ensures your vegetable garden is full to the brim with healthy plants to provide bumper homegrown harvests.