Finally, March is here! The heralding of spring marks a pivotal moment for our gardens, which are beginning to awaken from their annual slumber. It’s a prime time for seed starting, and there are so many wonderful flowers you can plant this month that will fill gaps in beds and borders, and create abundant pots and hanging baskets. Growing these flowers from seed now will make substantial savings compared to buying nursery plants later in the season, and provide you with an endless choice of varieties in every color imaginable.
In many regions, the weather remains too cool for planting seeds in the garden without any protection from the elements. While winter sowing seeds is possible for hardier varieties, starting seeds indoors is the best option for most gardeners, allowing greater control over the quality and position of the young plants. Provide the right light, temperature, and moisture levels, and you'll be ready to transplant seedlings into the garden as soon as the last frost date has passed.
Myriad annual and perennial flowers can be started in March, but certain varieties are destined to be star performers when planted at this time. Many of these flower seeds are available in the Gardening Know How Shop, which only stocks the best varieties, handpicked by experts.
In addition to these flowers, you can also plant any of our must-sow flower seeds for February during March. Happy growing!
From sensational flower seed collections to grow kits, seedling trays, and drip-irrigation lids, the Shop has everything you need to create your dream garden.
1. Cosmos
Cosmos are favorite flowers to grow from seed – and for good reason. Their captivating blooms – which come in infinite petal styles and colors – have a delicate appearance that belies their resilience and adaptability to most soil types and weather conditions. They are fairly drought tolerant once established and their presence will entice butterflies, bees, and other precious pollinators to your garden.
Sonata cosmos, available in the Gardening Know How Shop, have a classic look but are more compact than taller types such as Sea Shells cosmos, making them ideal for containers or the front of borders.
For something more unique, try Cupcakes and Saucers cosmos, which have curved petals that form a bowl shape.
To grow cosmos, thinly scatter seeds across the surface of seed-starting mix and lightly cover them. Keep them warm and moist and thin out seedlings once they reach a few inches in height. Once they have developed two or three sets of true leaves, pinch out cosmos to encourage fuller plants.
Transplant young plants into the garden once the risk of frost has passed, and water regularly until they establish.
2. Lobelia
Lobelia is a container garden staple that blooms all summer and into fall with a mass of tiny blue, purple, or white flowers that cascade over the sides of pots and hanging baskets. While they thrive in full sun, the plants will also tolerate part shade, making them a versatile choice.
March is an ideal time to start lobelia from seed, as they need to be started 8 to 12 weeks before being planted out after the last frost date. Scatter the seeds over the top of moist potting mix and cover with a clear plastic lid to keep in the moisture. You can find a range of professional-quality seedling trays and lids in the Gardening Know How Shop.
Place the tray in a warm, sunny spot. Carefully prick out seedlings and transfer them into individual pots, giving them plenty of light and moisture until planting time, when they need to be hardened off before planting out.
3. Calendula
Calendula, commonly known as pot marigold, is a versatile annual that thrives in cooler temperatures, bookending summer with blooms early in the season then springing back to life as the heat fades. Although, in cooler areas, it will endure through the whole summer into fall.
Despite the name, the flower is not in the same genus as marigolds (tagetes) and has different properties. Its flowers are more daisy-like and possess a pleasant scent, while marigolds exude a more pungent smell that repels pests, making it a prized companion plant on the vegetable plot. However, calendula attracts pollinators and can be used as a trap crop to entice certain pests away from your veg. Unlike marigolds, calendulas are edible. They are also medicinal, used historically to treat wounds and reduce inflammation.
Orange Flash is a gorgeous calendula variety that makes a delicious healing tea. It’s part of our Natural Remedies Seed Collection, available in the Shop.
Calendula can tolerate some frost so can be sown direct in the spring or started indoors a few weeks before planting out – scatter lightly across potting mix and cover with a thin layer of soil on top.
4. Dianthus
Dianthus, often called pinks, are beloved for their long-lasting frilly flowers with a clove-like fragrance. They have a pretty, elegant look, elevating borders, rock gardens, and containers while attracting pollinators. Yet plants are hardy and easy to grow. Many varieties are perennials or biennials, returning year after year with minimal care.
Available in shades of pink, red, white, and bi-color variations, dianthus also comes in a stunning lavender-blue Siberian blue variety, part of the Flower Seed Bio Dome Collection in the Shop.
To grow dianthus from seed, sow indoors 8-10 weeks before the last frost, pressing them lightly into moist soil without covering. Keep them in a warm, sunny spot and once seedlings have a few sets of leaves, harden them off and transplant them outdoors in well-drained soil with full sun. Deadhead regularly to encourage more blooms.
5. Dahlias
Dahlias are most widely purchased as tubers, yet many types can be grown from seed and may even flower in their first year. While you won't be able to grow the heavily hybridized varieties in this way, each plant is genetically unique, so you can experiment with creating your own types. It’s a wonderfully cost-effective way to add these popular perennials to your garden, and with proper care they will last for many years.
Dahlias flower from late summer into fall, making a stunning display when most of the garden is winding down for the season. The flowers are prized for cutting gardens and are even edible – tubers and all.
To grow dahlias from seed, start indoors 6 to 8 weeks before your expected last frost date. Sow seeds into individual modules or pots, or spaced out in seed trays, sprinkle over a light layer of potting mix – about ⅛ inch – and top with a lid or other plastic cover. Place in a warm spot until the seedlings start to develop, which should take about 2 weeks. Then move them to a sunny windowsill until they develop, transferring them into bigger pots if necessary. Harden off seedlings and plant out after the risk of frost has passed
6. Petunias
Indispensable for filling containers and hanging baskets, sunny petunias need to be started early in the season to maximize their flowering window, which runs from late spring until the first frosts of fall. Sowing seeds in March will give just enough time to get plants off to a good start.
Petunias come in a wide range of colors and forms, but Double Cascade petunias, available in the Shop, are one of the most stunning varieties, with frilly, abundant flowers, perfect for planting statement containers.
Thinly sow the seeds across the surface of moist potting mix and place them in a warm, bright spot. Keep the soil moist and transplant into final positions after the last frost has passed.
7. Sweet Alyssum
Sweet alyssum blooms for months on end with its frothy white flowers. With its low-mounded growth habit, it's a perfect edging plant and makes dreamy containers. It's quick to grow from seed and can be succession sown for a continual sea of elegant blooms throughout the growing season.
Normally, sweet alyssum is sensitive to heat, but Snow Crystals Sweet Alyssum, available in the Shop is an award-winning variety that is heat resistant, meaning that its blooms can span three seasons.
Sow seeds over the top of moist potting mix, and cover with a thin layer of compost. Place in a warm, bright spot and, once the last frost date has passed, harden off seedlings before planting.
More Flower Growing Inspiration
- Discover the best romantic old garden roses to grow for a dreamy display.
- Be enchanted by these 8 blue flowers you can grow from seed for vibrant beds and containers.
- Try these 7 small flower bed ideas for big blooms in compact corners.
- Browse glorious flower seeds in the Gardening Know How Shop, selected for their beauty and performance.
This article features products available from third party vendors on the Gardening Know How Shop.
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