Gardens will soon be full of ‘thriving’ flowers if you plant these seeds now

Summer will be here before we know it, even if it feels right now like we’ve been grinding through cold and wet days for months. And if you want a vibrant, colourful garden to bring joy to your life (and impress your guests) this summer, you don’t have time to waste — you need to get moving now. 

It may only be March, but this is when you can sow the seeds (literally) of a thriving garden that you can enjoy all summer long as the evenings get longer and warmer. What’s more, if you choose perennials, you’ll get them returning year after year to brighten up your summer days. 

But if you want gorgeous summer blooms that return year after year, you should get started by planting your perennials indoors in late February or early March. Do this, and you can have outdoor-ready plants just as any last frosts of the spring stop in April. Here’s our choice of flowers to plant in March to have thriving and colourful blooms all summer. 

1. Black-eyed Susans

Sara Rubens, certified garden coach and founder of Seed to Sanctuary, told Real Simple: “Black-eyed Susans are a classic for any garden! These cheery yellow flowers with dark centres bloom year after year and are super easy to grow.”

The RHS says this flower is “a moderately fast-growing, evergreen, perennial twining climber, often grown as an annual”. It reaches 2.5m tall and has heart-shaped to oval toothed leaves. it produces flat, salver-shaped, orange to yellow flowers with dark brown centres which flower from summer to early autumn.

To start black-eyed Susans from seed indoors, sow the seeds 10 weeks before your last frost, and plant seeds a quarter of an inch deep in seed trays, Rubens advises. The RHS says you should grow them in well-drained soil in full sun with a support for the plant to climb.

2. Coneflower 

These are easy to grow and hardy perennials, which the RHS says are “increasingly popular in gardens”.  They flower in late summer and combine well with other late perennials and grasses. The flowers are attractive to bees and butterflies. They produce large daisy-like flowers in white, pink, red or orange.

Chrissie Handley, lawn care specialist at Online Turf, told Real Simple: “When starting them from seed, you’ll want to make sure they’re kept consistently moist and positioned near a consistent light source, as they take a lot of sunlight to be able to germinate properly.”

The RHS adds that they need a position in full sun in soil that drains easily and do not flower freely in shade.

3. Lavender

Lavender grows distinctive and richly fragrant flowers and foliage. It’s an easy-to-grow shrub that thrives in sunny spots, whether that’s in free-draining soil or in a container, and flowers in late spring and through summer. It’s a hardy plant with evergreen foliage but it’s best not to plant lavender in cold, damp spots. 

The RHS says lavender is “best planted in April or May as the soil naturally warms up and when many fresh plants become available in garden centres”. But you could start it off indoors given how tough it is and how well it grows in containers. You can then transfer it outside later in the Spring. As well as growing well in containers, it also looks great in flower borders, herb gardens and as a low hedge or edging to a border.  

4. Delphinium

This striking perennial is known for its rich colours. It flowers in early summer and is perfect for beds and borders. It’s easy to grow and will flower all summer. 

The RHS advises that delhiniums like “free-draining soil in an open, sunny site with shelter from strong winds” but that they “won’t grow well in shady sites or poorly drained soil”. It adds: “Very heavy clay soils will need improving. They also need plenty of space and don’t grow well if crowded or shaded by other plants.”

Chrissie Handley, lawn care specialist at Online Turf, told Real Simple: “Delphiniums love a cooler temperature when germinating, so starting them in winter is ideal. Starting them indoors also means you can control the temperature to make sure they’re kept cool. Delphiniums take a while to flower, so planting them indoors early means you’re more likely to see the blooming flowers in time for summer.” 

5. Geraniums

Geraniums are hardy and striking flowers that also work well as ground cover under shrubs and trees as they are happy in either full sun or partial shade. Gardening site Sarah Raven says: “Geraniums are not too fussy about soil types — like most things they prefer it moist and well drained, but once established they can survive in the rain shadow of walls, shrubs or trees.”

They can be planted from March to May. If you plant them during this period, you will get them established before the hot weather  kicks in and will be rewarded with flowers all summer. You can start it off planted in a pot, before teasing it out of the pot and putting it in the ground.