By Sarah Wilson
It’s easy learning how to grow zinnias so you can fill your summer garden with bright splashes of feel-good color until the first frosts. All it takes is a simple packet of seeds for an easy transformation that will soon put the wow into your garden planting.
There are lots of varieties of these lovely half-hardy annuals to choose from. The simple, single-flowered versions loved by bees include varieties like the elegant ‘Red Spider’ with its narrow bright red petals, which grows up to a rangy 90cm tall. There are shaggy cactus-flowered zinnias too that are known as semi-doubles, as well as the single ‘Envy’, which comes in zingy lime green and grows up to a metre tall. The pompom varieties will hog the limelight when cut and arranged in vases. The elegant double flower forms are like chrysanthemums, just better groomed.
These good looking flowers are native to Mexico and their range of gaudy colours pays homage to their homeland. In recent years many fashionable pastel and peachy shades have been added that come in beautiful soft tones.
It’s the taller, larger flowered varieties that pack a dramatic punch in flowerbed ideas and are so striking in vases. Once you've followed our tips on how to grow zinnias, they will flower from July right into autumn (as long as you keep deadheading), punching well above their weight all summer long.
How to grow zinnias: key points to remember
Follow these key pointers for how to grow zinnias and help your plants thrive:
- Zinnias are easy to grow
- Seeds can be sown as late as May
- They do well if sown where they’re going to flower
- They do best in full sun, so position them in a spot where they can soak it up
- If soil is poor add well-rotted manure before planting
- The better the soil, the taller they will grow
- Tender plants are vulnerable to slugs in the first few weeks so keep an eye on them
- Flower prolifically from midsummer onwards
- They keep flowering if you dead head them
- Taller varieties make excellent cut flowers
- Cut them and they will come again
How easy is it to grow zinnias?
If you're wondering how to grow zinnias, the good news is that they are an easy plant to grow. It’s simply a case of giving them what they like (sun, fertile soil, space to roam) and avoiding what they don’t like (waterlogged soil, being cramped, cold conditions). Then you can simply sit back and enjoy the show.
How to plant zinnias
You can buy zinnias as plug plants, which is ideal if you want to learn how to grow zinnias and get off to a flying start at the beginning of the growing season. It's also a good option if you don’t have the space needed for how to grow flowers from seeds at home. Just be aware that mail-order plug plants can be shaken up in the post, and end up getting bruised which can lead to problems with diseased plants.
Carefully unpack your plug plants and keep them in indoors until needed. Once the risk of frosts has passed it's time to plant them up in good garden soil or compost containing John Innes No 2. Zinnias are half hardy and won’t like cold night time temperatures so don't be tempted to plant them out too soon.
As they develop, support the tall varieties with canes and string or with pea and bean netting stretched horizontally. When they’re about 45cm tall, nipping out the main buds encourages them to branch out and grow bushier. There's more climbing plant support ideas in our feature.
How to sow zinnia seeds
Prefer to know how to grow zinnias from seed? Zinnia seeds sown straight into the soil outside are less prone to being attacked by disease but seeds sown indoors or also have a good chance of flourishing.
If you're sowing zinnia seeds indoors, sow them in any good seed compost at the beginning of spring and transfer to a heated propagator, sunny windowsill or find a suitable spot in your greenhouse ideas. Avoid the temptation to sow earlier than this as you want sturdy and compact plants not leggy specimens that will struggle.
Sow two zinnia seeds to a pot or module, then thin out the weakest seedling to leave the strongest of the pair. As long as they have room to roam they will be happy, but if they seem to be outgrowing their space it's time to pot them on. Toilet roll tubes or newspaper pots allow you to do this without upsetting them.
If you're direct sowing seeds in the ground as your chosen method for how to grow zinnias, do so from the end of spring (around May) onwards. Choose a sunny site in garden borders, or where you can sow a row or two for cutting, such as in your raised garden bed ideas. Fork over to break up the soil. Rake well to create a crumbly bed for the seeds. Check the seed packet for spacings.
Sow seeds directly in the ground and cover with a thin layer of soil. Water thoroughly. Thin to 40cm apart after seedlings have sprouted, making sure not to uproot any staying behind.
Do zinnias need full sun?
For best results when it comes to how to grow zinnias, choose a spot in full sun, Zinnias like plenty of sunshine, as you’d expect as they come from Mexico.
Choose a sunny spot that’s sheltered, especially if you are growing taller varieties, to protect them from the wind. Then sit back and watch as these sun-baked beauties shoot up.
Can I grow zinnias in a container?
Zinnias will thrive in your container gardening ideas. If you're choosing this option for how to grow zinnias, make sure you choose a large container that has drainage holes in the bottom. The taller the zinnias you have in mind, the larger the container should be.
Don't forget to factor in how much space you'll need to accommodate your plants. Planting them too close is one of the container gardening mistakes to avoid. Zinnias require good air circulation between each other so plants should be spaced well apart.
Position the container in a sunny spot then fill it two-thirds full with a light potting mix that contains organic matter. This will allow for the good drainage that zinnias require, as they hate getting waterlogged. Water in well. Give them a liquid feed every couple of weeks to encourage more blooms.
Do zinnias come back every year?
Annual varieties of zinnia last for one season only. They’re half-hardy annuals so are a tender plant and will die during the first frosts of autumn.
Try saving seed from them beforehand though and using it to propagate your own new plants the following spring.
Do zinnias self seed?
Zinnias begin to form seeds as soon as the flowers start to fade. Dead heading during the growing season encourages new blossoms but interrupts seed production. Seeds drop from faded flowers in autumn and germinate in spring when the soil starts to warm up.
You can capitalise on this to plant zinnias in a place of your choosing so you can better control your garden design ideas. Collect seeds from the most colorful and strongest plants in your collection. Any weak and spindly plants or those susceptible to disease should not be used for seed harvesting.
Allow the zinnias to dry out and complete their life cycle. They are ready to harvest once the petals have dropped off and the flower head becomes a seed pod. Place a small paper bag over the flower head, or cut the flower head and hang it upside down in the paper bag. Store in a clearly marked envelope.
What problems affect zinnias?
- When you’re sowing seeds in a propagator or on the windowsill, everything must be clean (pots, trays and so on) and fresh compost is essential. Find out how to compost in our guide.
- Always water young zinnias in pots or plugs with tap water, never with water from a water butt which can harbor fungus.
- Don’t overwater as this can have an impact on your success with how to grow zinnias. Brown blotches on the leaves are caused by overhead watering so direct the spout of a watering can at the soil rather than using a sprinkler where water will hit the leaves.
- If your zinnias are planted too close together they will develop dusty looking white mildew so remember to space them generously.
Do zinnias make good cut flowers?
Zinnias are one of the best cutting garden flowers. With their bold shapes and vibrant or softly pastel colors, plus impressive productivity, they make easy to grow cut flowers for the house. They also have a long vase life.
Always make sure you pick zinnias with stiff stems before cutting. Pick them just as the buds are opening. With flower food in the water they will last up to 10 days.
Zinnias work well arranged in single stem vases. If you like to mix things up in a larger vase, be sure to choose some lime green ones too like ‘Envy’ and ‘Benary’s Giant Lime’ that combine well with other colors. Stick with either a pastel or bold color theme for the best results.
Where to buy zinnias
There are several options if you are interested in how to grow zinnias. Grow them from seed or pick them them young plug plants from the garden center or online. Shop zinnias at the below suppliers, or keep scrolling for some of our favorite picks to try in your own plot.
Where to buy zinnias in the UK:
- Shop zinnias at Amazon
- Shop zinnias at Crocus
- Shop zinnias at Dobies
- Shop zinnias at Sarah Raven
- Shop zinnias at Suttons
- Shop zinnias at Thompson & Morgan
- Shop zinnias at Waitrose Garden
- Shop zinnias at You Garden
Where to buy zinnias in the US:
4 varieties of zinnias to try in your garden
With so many wonderful colors and varieties to choose from you're spoiled for choice. Here's a round-up of some of our favorite zinnia varieties.
Zinnia elegans 'Isabella' from Sarah Raven
This dahlia-flowered zinnia comes in an unusual pale lemon color and is great for flower arranging. Plant it in full sun in well-drained soil for the best results. It grows to a height of around 70cm and will need staking. Deadheading is necessary to prolong blooming.
Zinnia elegans 'Whirlygig Mixed' from Thompson & Morgan
Each distinctly marked, brightly colored, semi cactus-like bloom has contrasting petal tips. This variety is an outstanding performer, freely flowering throughout summer and growing to 60cm. The vibrant flowers are ideal for attracting bees and butterflies.
Zinnia Lavender Queen from Suttons
This stunning cut flower has long straight stems, pretty foliage and huge dahlia-style blooms in pastel shades. They match dahlias for size and presence, yet provide more blooms and for a longer time. This variety is both a florist's and a gardener's dream come true.
Zinnia 'Queen Red Lime' from Dobies
The exotic looking flowers of ‘Queen Red Lime’ come in pastel shades of deep pinky-red brushed with lime green. The flowers look fabulous both in the garden or a large container. They do well if given free drainage and full sun, growing to a height of 60cm.
Sarah Wilson has been a lifestyle journalist for many years, writing about gardens since 2015. She's written for Gardeningetc.com, Livingetc, Homes & Gardens, as well as Country Homes & Interiors and Modern Gardens magazines.
Her own (small urban) garden is a work in progress - so many ideas, not enough space to cram them in. Hero plants include her ever growing collection of ornamental grasses, black bamboo and ferns, and the perennials like salvias and penstemons that come back reliably year after year. All very restrained though when in fact she'd love to pack her garden with gaudy dahlias and giant cannas, so these are top of her wish list for what to grow next.
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