As the last of the cold recedes in the spring, May is an important window for gardeners to sow their summer flowering seeds.

This is the month when the soil warms, the sun lingers, and the garden starts to stretch into its growing season. With the right choices, you can fill beds, borders, and containers with vivid flowers that carry your garden through to autumn.

Planting petunias

May sits at a sweet spot in the growing calendar. In many places, the danger of frost is behind us or quickly diminishing, giving young plants a chance to settle in without sudden setbacks.

With warmer soil temperatures, seeds sprout more quickly and seedlings grow more vigorously. Spring rains still leave the soil moist, while the increasing warmth and longer days help plants gain a solid footing early on.

This early advantage lets flowers planted or seeded in May settle in well before the peak of summer heat. With more time for roots to develop and foliage to thicken, plants are better prepared to produce healthier and longer-lasting blooms.

Summer flowers (marigolds, petunias…)

There are many summer annuals that can be planted in May, but some perform particularly well when started at this time. These eight choices are dependable and bring both bright color and practical benefits to the garden.

Zinnias seedlings
Zinnias

Zinnias rank as some of the most rewarding annuals to grow from seed. They sprout quickly in warm soil and develop sturdy, upright flowers in a broad spectrum of colors—from vivid magentas to gentle pastels and striking bicolors.

Once established, they handle heat well and tolerate dry conditions, making them a reliable choice for both beds and fresh-cut arrangements.

Zinnias are ideal for garden borders or mixed beds, but they also shine in cutting gardens where you want continuous flowers to bring indoors.

African Marigolds
African Marigolds

Marigolds establish quickly and hold up well through the summer, making them a dependable fixture in many gardens. Their blooms appear early, often extending well into the heat of the season.

  • French marigolds (Tagetes patula) stay compact and bushy, lending themselves well to borders and container planting
  • While African marigolds (Tagetes erecta) develop taller stems with large, showy flowers.

Both varieties flourish in full sun with average soil and tolerate occasional dry spells without too much stress.

Bonus: The distinctive scent of marigolds can also help to deter certain pests, which is especially useful near vegetable patches.

Petunias
Petunias

Petunias have a prolonged flowering season, often lasting late into fall if regularly deadheaded. There is a diverse variety available—from trailing types that cascade gracefully in hanging baskets to more upright, compact forms that fill beds and pots with dense blooms. These flowers are a great option for particularly sunny gardens.

Cosmos flower with a bee
Cosmos

Cosmos bring a soft, airy quality to summer planting schemes. Their finely divided foliage and daisy-like flowers attract bees, hoverflies, and butterflies. These flowers cope with a little neglect—too much fertility will lead to more leaves than blooms—so they’re well-suited to poor or sandy soils.

Cosmos are especially good for naturalistic borders, wildflower-style plantings, or informal gardens. They’ll self-seed gently in mild climates, returning in future seasons with minimal effort.

Teddy Bear sunflower
Teddy Bear Sunflower

Sunflowers are iconic summer flowers, with cheerful, towering heads that follow the arc of the sun. They’re quick to germinate and develop, making them a fun project for children and a bold feature in ornamental or edible gardens.

  • Tall varieties like ‘Russian Giant’ or ‘Mammoth’ make impressive backdrops or screens;
  • While dwarf cultivars such as ‘Teddy Bear’ or ‘Little Becka’ suit pots or small gardens.

They grow best in full sun and well-drained soil and benefit from staking if exposed to strong winds.

Nasturtiums
Nasturtiums

Both ornamental and edible, nasturtiums are a good all-rounder in the garden. They spill attractively over container edges, raised beds, or retaining walls, and their round leaves and bright flowers add a tropical note to planting schemes.

Nasturtiums don’t need rich soil—too much fertility reduces flowering. They’re also known for their role in integrated pest management, acting as a trap crop for aphids and other sap-suckers. Both the leaves and flowers are edible, with a peppery flavor that works well in salads.

Salvia Splendens
Salvia Splendens

Salvias provide intense, saturated color and upright structure to flower beds. Their tubular blooms are irresistible to bees and hummingbirds, making them a valuable part of any pollinator-friendly garden.

Red-flowered Salvia splendensis bold and tropical, while Salvia farinacea (‘Victoria Blue’, for example) adds cooler tones and a looser, more relaxed habit.

Most salvias prefer full sun and good drainage, and once established, they are among the more drought-tolerant annuals available.

Coneflowers and a Monarch Butterfly
Coneflowers

Although typically grown as a perennial, Echinacea can also be sown or planted in May for flowering later the same summer. These tough, clump-forming plants are native to North American prairies and have excellent drought resistance once settled.

The large, daisy-like blooms with raised centers attract pollinators and birds alike, especially goldfinches in late summer. Coneflowers blend well into mixed borders and naturalistic designs, where they add both structure and ecological value.

Tip: Leave some of the coneflower seed heads uncut to provide attractive winter interest once the flowering season is over.

Planting petunias
  • Water deeply: Give new plants a good, deep watering right after planting. Even those that love the heat need steady moisture to get their roots established. Soaking the soil deeply encourages roots to grow down instead of staying near the surface, which helps plants handle dry spells better later on;
  • Mulch: Adding a layer of mulch (about two to three inches of something like composted bark or straw) can make a big difference. It keeps the soil from drying out too quickly and helps keep weeds from taking over, but make sure not to pile it up right against the stems to avoid any rot problems.
  • Choose a sunny location: Look for spots that get plenty of sun. Most of these flowers need at least six hours of direct sunlight to bloom well and grow strong. Planting in too much shade often results in sparse blooms and leggy, weak plants.
Colorful petunias on a fence

May is a turning point in the garden, when the soil is ready, the days are long, and the conditions are ideal for planting flowers that will carry the season’s color.

By choosing reliable performers like zinnias, cosmos, or salvia, and giving them the right start, it’s possible to create a garden that not only looks vibrant but also supports a thriving, biodiverse garden.

Whether you’re filling borders or just a few containers on a sunny balcony, a thoughtful selection now means months of beauty ahead—with color, scent, and pollinator activity right through to autumn.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *