The Only Flower Seeds You Need to Sow in March – 7 Fool Proof Blooms for a Show-Stopping Summer Garden

This month sees the arrival of longer days and warmer weather, and there is a feeling that summer is definitely on the way. So my thoughts always turn to the best flower seeds to sow in March, and the ones I have come up with are fool proof.

Sowing my own seeds is always rewarding but especially so when it means filling my garden with all my favorite flowers. There is a huge range of plants that are quick and easy to grow in this way, and growing from seed is a much more affordable option than buying young plants at the garden center.

Choosing a range of flower types that bloom at different times will also give you a longer flowering season, so there's always something to admire and pick for the house. To help you choose what to plant in March, this is my shortlist of flowers to sow in March that will complement your garden planting from spring right through to fall.

1. Zinnia

Easy to grow zinnias are one of my favorites to fill the summer garden with vibrant color that lasts right up to first frosts.

Plant a packet of zinnia seeds now for a supply of never-ending flowers that are good for cutting too, particularly the long-stemmed varieties. Even better when you cut them for the vase and they always come again.

Zinnias do well if sown where they’re going to flower, especially in full sun. If you want to direct sow seeds in the ground now you can do so if you live in a region where spring warms up early.

First prep the soil so it has a crumbly texture then sow seeds directly in the ground (check the packet for suggested spacing), and cover with a thin layer of soil. Water thoroughly.

Once seedlings have sprouted, thin to 15 inches apart, as zinnias grow into bushy plants that need space. If you miss the March window zinnia seeds can still be sown outdoors as late as May.

You can also sow zinnia seeds indoors in trays or pots of seed compost. Transfer to a heated propagator, just like this great kit from Amazon, if you want to give them a head start, or alternatively try a sunny windowsill. Pot healthy ones on if they're outgrowing their space.

Zinnias begin to form seeds as soon as the flowers start to fade, dropping into the soil and germinating in spring.

Last year I grew a stunning mix of double-flowering dark pink 'Amethyst Treasure', available from Burpee, together with crisp green 'Tequila Lime', also available from Burpee. I deliberately left the dead flowers in place so they could self-seed so fingers crossed for a repeat show this summer.

2. Sweet peas

These gorgeously scented beauties are stars of the flower garden as well as being one of the best cutting flowers. In warmer regions, you can sow sweet peas early in the season and they can even handle light frosts. But I always forget and for me March always feels about right to start them indoors.

This year I'm trying Eckfords Finest Mix Heirloom sweet pea seeds from Burpee in pretty shades of shell pink, maroon, violet, cream, blue, and crimson striped with white. Early sowing is the secret of success, especially as seeds can be slow to germinate outside if conditions aren't right.

So I always start mine indoors. They develop long roots so I plant them in these root trainers from Amazon. You can also use the cardboard part of toilet rolls but they can get soggy.

Fill containers with seed compost, and sow the seeds about half an inch deep. Water thoroughly before transferring to a cold windowsill. It takes seeds up to three weeks to germinate. Once they're showing their first leaves transfer them to larger pots.

When plants are around 4 to 6 inches tall, pinch out the central growing tip, just above a leaf joint, to encourage strong growth.

3. Nigella

One of my go-to flowers, nigella (Love in a Mist) is the perfect choice to fill the gaps in summer borders. The seeds can be sown successionally every few weeks from spring right through to summer.

Simply sprinkle the seeds wherever you want them to grow, cover them lightly with soil, and up they pop. They are also prolific self-seeders once established in your garden.

Nigella will thrive as long as the plants don't get too hot, as they prefer cool weather conditions. This means these hardy annuals are also one of the flowers to sow in fall if you want to get a head start on the season.

Nigella flowers will grow in nearly any soil, so long as it is well-draining. So if the soil is hard and compacted you will have to prep it before sowing seeds.

Find the prettiest blue nigella seeds at Amazon to add to your list of the easiest flower seeds to sow in March. There are also white and pink varieties of nigella available.

4. Nasturtium

Another great choice for flower seeds to sow in March are nasturtium. The seeds are easy to sow and grow quickly into vigorous spreading plants, which means they can be used to fill gaps in summer flowerbeds. Choose climbing varieties of nasturtium, which have longer stems that travel further to fill spaces quicker.

Sow nasturtium seeds directly in the garden after all danger of frost has passed. Choose a sunny spot in free-draining soil.

Seeds will germinate in 7 to 14 days. Then thin the seedlings to about 14 inches apart for trailing varieties. Water regularly throughout the growing season, and they will flower from summer through to fall.

I'm not a huge fan of either orange or yellow flowers, which are both popular nasturtium colorways, but I love red flowers so this year I'm trying these fabulous 'Troika Red' nasturtium seeds from Burpee (pictured above).

As well as being long flowering, the best nasturtium varieties are a good choice if you're looking for plants for pollinators. Don't forget you can add the flowers to the salad bowl too, and for this reason they make it onto our list of the easiest edible flowers to grow from seed too.

5. Stocks

These sweet-smelling flowers add fragrance and beauty to any garden border, and are one of my favorite scented flowers. When I smell their perfume I know that summer's truly here.

Because of their scent they are one of the best plants for pollinators too. But you will have to be patient with this flower variety as you sow seeds now for blooms next summer.

The flowery spires come in some quite vibrant shades of pink, purple, and mauve, as well as softer tones of peach, pale lemon and cream. Stocks are one of the classic cottage garden plants to add to your planting design, and I think there is something timeless about them.

The good news is they're easy to grow. In March it's best to sow seeds in a tray indoors, scattering them thinly on a layer of seed compost, then sprinkling over a dusting of fine soil.

Cover with a transparent tray lid, then transfer to a sunny windowsill until they germinate. When the seedlings have two true leaves, prick them out into pots and grow them on. In early fall, plant them out where you want them to flower next year.

You can also sow seed directly into the ground in early summer. The young plants will overwinter in the garden and flower the following summer.

6. Poppies

My favorite poppy varieties are the flouncy oriental ones with splashes and splodges on their petals. This flamboyant type of poppy has large, vibrant blooms that add a bold note to summer planting.

Poppies are easy to grow from seed directly where you want them to flower, as long as the soil is well-raked. Most poppies thrive in moist but well-drained soil in full sun. Start sowing seeds in spring, staggering your sowing to ensure a continuous show.

Check seed packets for more specific information about how different poppy varieties should be sown. Essentially you can scatter the seeds and leave them to get on with it. There is no need to cover them with soil. The seeds are small and easily blown away so mix them with a little sand to make the job easier.

I like to stick with one color rather than a mix. These striking white poppies with a dark violet spot in the center from Amazon will pretty much go with any planting scheme.

7. Coreopsis

If you're looking for a long-flowering choice of flower seeds to sow in March try coreopsis (tickseed). It produces masses of vibrant yellow, red or orange daisy-like flowers, often splotched with contrasting markings, and is a native flower that blooms from summer through fall.

Easy to grow from seed, in March coreopsis can be sown in the ground where you want it to grow. Seedlings from direct-sown seeds should then be thinned to around 6 inches apart.

Alternatively coreopsis can be sown in seed trays under cover from late winter to early spring then grown on in pots before being hardened off and planted out.

Choose a hardy herbaceous perennial variety of coreopsis like Li'l Bang™ Firewheel from Nature Hills, a real stunner with fiery red and golden-yellow blooms that last from early summer to fall, and self-seed to come back every year.

A must for prairie planting, coreopsis is also good for wildflower meadows.

That's our round-up of the best flower seeds to sow in March. When you're planning your seed sowing schedule for March, also check out the biggest seed sowing mistakes to max up your chances of success.

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