Zinnias have always been popular summer flowers, and with their variety of colours and abundant flowering, they are a true delight for every gardener. Read on to find out more about zinnias and get tips on growing them in your own garden.
Zinnias (Zinnia elegans) can be found in almost every cottage garden in summer. They are often used as cut flowers, as they produce numerous colourful flowers throughout the summer. Discover all there is to know about zinnias, how to plant them, their location and care requirements, as well as tips on sowing zinnia seeds.
Zinnias: origin and characteristics
Zinnias belong to the large daisy family (Asteraceae), just like daisies (Bellis perennis) and dahlias (Dahlia). There are about 20 species in the genus Zinnia, which grow as annuals, perennials, or as half-shrubs. The main variety planted here in the UK is Zinnia elegans. This annual summer flower is originally from Mexico and is also found in other areas of Central and South America. Zinnias were given their name by the famous Swedish botanist Carl von Linné in honour of the Göttingen anatomist and botanist Johann Gottfried Zinn.
Zinnias are annual summer flowers that grow upright and bushy. Zinnia leaves are characteristically covered with short hairs and are therefore rough to the touch. They sit opposite each other directly on the flower stalk and are almost triangular in shape. A terminal flower forms at the end of each stem, which, depending on the variety, can be double or single. Zinnias bloom in many colours, from white to yellow, orange, and red to dark pink. However, strong colours fade quite quickly in strong sunlight. The flowering period for zinnias stretches from July to September, occasionally into October.
Tip: zinnias are bee-friendly ornamentals, providing nectar to eager pollinators such as bees, bumblebees and butterflies. Although each flower produces a relatively small amount of nectar, the sheer number of blooms compensates for this.
The most beautiful zinnia varieties
If you want to plant zinnias, there is a huge selection of varieties and different species of the genus Zinnia to choose from. They differ mainly in colour, shape and size of the flower as well as growth height. Whilst tall-growing cultivars are best for plant beds, small-growing dwarf zinnias are better for growing on the balcony. Here are some of our favourite varieties of zinnias for all locations. All varieties mentioned belong to the species Zinnia elegans.
- ˈLiliputˈ: low-growing zinnia mixture of different coloured, small plants with a growth height of only 50 – 60cm. ˈLiliputˈ zinnias bloom from July to October.
- ˈPeter Panˈ: dwarf zinnia with a height of only 30cm and about 8cm large flowers that bloom in orange yellow to blood-red.
- ˈPolar Bearˈ: almost completely double white zinnia with large flowers and plants up to 1m high.
- ˈGiant Cactusˈ: 60 – 80cm tall zinnia variety with semi-double, large flowers and slightly rolled petals reminiscent of cactus dahlias.
- ˈThumbelinaˈ: smallest of all low zinnia varieties with a growth height of only 15 – 20cm and dahlia-like flowers in a wide range of colours. Ideal mini zinnia for small balcony boxes and pots.
- ˈWhirlygigˈ: colourful mix of two-tone zinnias that have various combinations of pink, orange, red and white, growing to around 60 – 70cm in height.
- Zinnia angustifolia: narrow-leaved zinnia with lavender-like leaves and small red, pink, deep orange, yellow or white flowers. These petite plants reach a height of about 30 – 50cm.
How to grow zinnias
Zinnias are extremely rewarding flowering plants, as long as you pay attention to their needs in terms of location, sowing and planting. Keep reading for important tips on how to successfully plant and cultivate zinnias.
When to plant zinnia
As annuals, zinnias need to be freshly sown every year. Start zinnia seeds on a warm windowsill in March and wait until after the last frost in mid-May to plant them out. You can also skip sowing zinnia seeds yourself and buy young plants to plant out around the same time.
Where to grow zinnia
Zinnias like warm, sunny and wind-protected spots. These ornamentals prefer loamy, sandy, nutrient-rich soil that stores moisture well. They do not tolerate waterlogged soil. Whether in the garden, in a pot or on the balcony, zinnias do well in the bed as well as in a container, as long as the location is right and their care needs are being met. That said, they do require regular rotation. Therefore, you will need to transplant them elsewhere or change their soil every year.
Tip: zinnias do not tolerate heavy rain, as this can damage the flowers and the tall-growing varieties can fall over. A sheltered location is therefore important.
Growing zinnia from seeds
Zinnias can be grown indoors between February and April because their seedlings do not tolerate cold and love the warmth. To sow zinnia seeds, first prepare a growing tray or small pot and fill it with a low-nutrient growing soil. During and after germination, zinnia seedlings require very few nutrients. A nutrient-poor soil also encourages seedlings to form strong roots. We can recommend our Plantura Organic Herb & Seedling Compost for this. Our seedling soil is low in nutrients, so is perfect for sowing zinnia seeds. It also has a loose structure and retains water well. As our compost is peat-free, it is a more climate-friendly option than conventional composts. After preparing the pots, sow the seeds into the soil at a depth of about 0.5 to 1cm and water well. Then, place the seed tray or pot on a bright windowsill at 16 to 20 °C and keep the soil moist, but not wet. It will take about 10 to 20 days for the seeds to germinate. As soon as the first true leaves form after the cotyledons, prick the seedlings out. Now pot the seedlings up individually into more nutrient-rich soil and let the zinnias grow a little cooler at 12 to 15 °C until they are ready to be planted out.
Move the young plants outdoors from mid-May to late June. Whether in a pot, balcony box or bed, keep a planting distance of 20 to 30cm between each plant. As zinnias grow quite bushy, they usually close the gaps quite quickly. For planting on the terrace and balcony, choose sufficiently large planters with drainage holes. For individual zinnias, the pot needs to have a volume of at least 5 to 10 litres, depending on the growth rate. Fill the bottom of your planters with a drainage layer of coarse gravel or expanded clay about 3cm high. Top it off with a nutrient-rich potting soil, such as our Plantura Organic Flower Compost. Our sustainably produced potting soil contains all the essential nutrients to promote lush flowering and strong plants. Now place the zinnia seedlings in the soil, observing the planting distance. After that, water thoroughly to flush the soil to the roots.
Summary: planting zinnias
- Sow: February – April
- Germination: after 10 – 20 days
- Plant out: mid-May – late June
- Planting distance: 20 – 30cm
- Location: Sunny, sheltered from the wind and warm
- Soil: Loamy-sandy and nutrient-rich
- Cultivation possible in beds or containers
Zinnias are thirsty plants that require a regular water supply. Keep the soil evenly moist, but never soaking wet. Avoid waterlogging to prevent root rot. Zinnias make fantastic cut flowers throughout the flowering period. To harvest cut flowers, use a sharp knife and cut the flower stalk back to a pair of leaves. This is where the plant will branch out again and form flowers. The flowers stay fresh in water for about a week or two.
Unless you intend to collect the seeds, remove wilted zinnia flowers periodically to ensure they keep blooming.
Like many summer flowers, zinnias depend on a regular supply of nutrients and need to be well fertilised. When fertilising zinnias in pots or balcony boxes, we recommend using a liquid nutrient fertiliser, such as our Plantura Liquid Flower Food, for instance. About every 2 weeks, add 15 to 25ml to 5 litres of water and water as usual. The benefit of using a liquid fertiliser like ours is that it reaches the roots directly and is absorbed quickly. You can also remedy acute deficiency symptoms, such as a yellowing of the lowest leaves due to nitrogen deficiency, this way.
Overwintering zinnias: are zinnias hardy?
Zinnias are not winter hardy in this part of the world, because they are not at all tolerant of frost. As is usual with annual plants, zinnias die off completely once the seeds are mature, so you cannot overwinter these plants indoors either. The seeds are the only part of the plant to survive until the following year.
How to propagate zinnias
Zinnias can be propagated from seed. Bear in mind that double flowers are infertile and do not produce seeds. As bees and other pollinators go from the flowers of one zinnia variety to another, the seeds often no longer contain the original variety of the mother plant. However, if varietal purity is not a priority for you, you may enjoy the gorgeous new colour combinations from home-grown seeds. To obtain your own seeds, do not deadhead your zinnias, but leave the faded flowers on the plants. The fruits will ripen until October. Once the plant has dried up in late autumn, remove the fruits and the flower head. Dry them indoors at room temperature for 2 to 3 weeks. Rub the flower head a little to release the seeds and separate them from any flower remnants. Store the seeds in paper bags in a dry, cool place. Zinnia seeds can germinate for about 4 years if stored well.
Common zinnia pests
Slugs love zinnias and can quickly kill off young plants, so protecting against snails makes sense, especially in the first few weeks after planting. Adult zinnia plants, on the other hand, are seldom at risk. Aphids and spider mites also like to infest zinnias from time to time. However, outdoors, beneficial insects such as the ladybird can prevent these pest populations from getting out of hand. For more tips on controlling aphids, see our separate article.
Are zinnias poisonous?
Zinnias are not poisonous as such, but the sap contains alkaloids such as nicotine and various terpenes which can cause irritation when they come into contact with skin. We advise always wearing gloves when cutting zinnias. Zinnia flowers, on the other hand, are edible and offer a real feast for the eyes as a decoration or ingredient in flower butter.
Sunflowers are distant relatives of zinnias, and can grow to amazing heights. Find out all about these popular summer flowers and learn more about planting, caring for and harvesting them.