Fast-growing flower seeds are one of the easiest ways to bring a fresh burst of colour to your garden before summer comes to an end. While spring is traditionally the busiest growing season, there are still plenty of flower seeds you can sow in July for blooms in a few short weeks.
As the name suggests, fast-growing flower seeds are those that you can plant in July to go from sowing to flowering in as little as six to eight weeks. This makes them ideal for filling gaps left by fading early summer or giving tired containers a late-season lift.
‘It’s all about choosing flowers that grow quickly enough to bloom before the weather turns,’ explains garden design expert, Jo McGarry from Caragh Nurseries. Luckily, there are several fast-growing varieties that are quick to germinate, easy to grow and capable of producing colourful blooms before autumn arrives.
1. Nasturtiums
‘Nasturtiums are a strong choice for fast colour and foliage as they grow quickly in warm soil, cope with poorer ground, and can be grown in containers, hanging baskets, borders or as ground cover,’ says Jo.
She says shorter or dwarf types are the best for July sowing. ‘They don’t need to put on as much growth before blooming.’
Richard Barker, horticultural expert at LBS Horticulture, also recommends nasturtiums for a quick colour display. ‘They usually germinate within seven to fourteen days, with some potentially sprouting in as little as five days,’ he explains. ‘After they have sprouted, plants will mature quickly and produce flowers after eight to ten weeks.’
Nasturtiums can be sown directly where you want them to flower, and a later sowing can ensure that you have flowers up until the first frosts. They also make great companion plants paired with vegetables for pest-control.
Where to buy nasturtiums:
2. Calendula
Calendula – widely known as pot marigolds – is a reliable choice if you want to bring a splash of colour to a tired garden border.
‘Calendula can germinate within a week or two after sowing, and should flower within six to eight weeks,’ says Richard. ‘The seeds can be sown direct where plants are to flower and need little attention aside from keeping the soil moist.’
As well as flowering quickly, calendula is a resilient choice for summer sowing. Morris Hankinson, managing director of Hopes Grove Nurseries, notes it’s particularly useful in warmer weather. ‘It’s notably drought-tolerant once established, and will self-seed for next year too,’ he says.
Where to buy calendula:
3. Sweet alyssum
‘Sweet alyssum is one of the quickest flowers to sow in July, with blooms appearing in as little as 45 days,’ says Jo.
It works well at the front of borders, in pots and as soft ground cover where summer planting is starting to fade.
‘Sweet alyssum is great for filling gaps in quickly; they spread to around 10 inches and bring a honeyed scent to the garden, making it useful for refreshing patio pots and softening the edges of beds,’ adds Jo.
Where to buy sweet alyssum:
4. French marigolds
Often hailed as a superhero flower, few flowers deliver as much cheerful colour for so little effort as marigolds.
They germinate quickly, with some seeds sprouting within five days of planting, making them a great choice if you’re looking for a quick burst of colour before the end of summer. Just be sure to stay on top of deadheading as the blooms fade, which will keep them flowering for longer.
‘They usually take around six to eight weeks to produce flowers if growing from seed, with French marigolds growing faster,’ says Richard. ‘Planting in full sun can help to encourage the plant to produce plenty of flowers.’
Where to buy French marigolds:
5. Zinnias
If you’re willing to wait a little longer for your reward, zinnias are one of the most impressive fast-growing flower seeds to sow in July. While they typically take around eight to ten weeks to flower, they make up for it with their bold, jewel-like blooms and long flowering season.
‘Expect a slightly longer wait than some other quick growers, but zinnias reward it with some of the most vivid, long-lasting colour of any July sowing,’ says Morris.
Particularly suited to borders and raised garden beds, zinnias continue producing flowers over long periods. ‘They can be sown outdoors directly into the soil where you want them to grow, and picking flowers regularly keeps more coming,’ adds Richard.
Where to buy zinnias:
6. Cosmos
If you’re looking for maximum impact from a late-summer sowing, growing cosmos is hard to beat. They might not be the fastest flower on this list, but they’re prized for producing masses of delicate blooms over a long season.
‘Cosmos are exceptional value for a July sowing because they flower over a long period, giving the best return for a late start,’ says Morris. ‘They can produce their first blooms in seven to ten weeks, then keep flowering right through to the first frosts.’
They’re also easy to grow from seed and will continue producing flowers well into autumn if you deadhead cosmos regularly.
Where to buy cosmos:
What are the most important tips for sowing flower seeds in July?
According to Morris Hankinson of Hopes Groves Nurseries, managing heat and moisture is the key challenge when sowing fast-growing flower seeds in July. ‘Sow in the evening to give seeds a cool overnight period to take up moisture before the heat of the day returns,’ he recommends. ‘Keep the soil surface covered with a light layer of compost or fine mulch to prevent the top few centimetres from drying out and crusting over, as this can stop germination altogether.’
Richard Barker, horticultural expert at LBS Horticulture, adds that while most fast-growing flowers need plenty of sunshine to bloom well, newly emerged seedlings can struggle during hot spells. ‘You’ll need to provide them with dappled shade in the hottest part of the day to prevent them from bolting or wilting,’ he says. There are several easy ways to shade plants in hot weather without having to move them if they’re already in the ground.
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If your garden is lacking colour, there’s still time to sow these fast-growing flower seeds and enjoy flowers before summer is over.
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