Growing and caring for zinnia

What you need to know about zinnia

Name: zinnia, Zinnia elegans, Zinnia haageana, Zinnia peruviana, Zinnia grandiflora (prairie zinnia).

Height: 15cm to 1m. 

Foliage: soft and velvety, light green linear to oval leaves attached directly to the stems.

Climate: warm temperate climates with hot summers.

Soil: will grow in most moist, well-drained garden soils.

Position: full sun is preferred; partial shade in very warm areas. 

Flowering: large, abundant, colourful single, semi-double or double daisy-like flowers from summer until autumn or the first frosts. 

Feeding: use a controlled-release fertiliser when planting, then liquid fertiliser every two weeks to promote further flowering.

Watering: water at least once or twice a week during warm summer weather. Can withstand dry periods once established.

Appearance and characteristics of zinnia

Zinnia can be an upright or spreading annual, perennial or shrub, but the annual flowering forms are most widely grown in gardens. These produce numerous single to double daisy-like flowers composed of large ray florets and small central disc florets. The broad selection of available colours ranges from red, orange and yellow to green, white and purple, in forms including giant double dahlia-like shapes and miniature pompoms. The tall upright varieties can be used in borders or as cut flowers, and the miniature varieties for edging garden beds or container growing.

Zinnia is part of the Asteraceae or daisy family, and the twenty species originate in dry grassland and scrub areas of the south-western United States, Central and South America. They are found widely throughout Mexico, where they were once cultivated by the Aztecs and noted by the Spanish during their conquests in the early sixteenth century. Zinnias are mainly hybrids developed from crossing Zinnia elegans, Z. haageana and Z. peruviana. They were named in honour of Johann Gottfried Zinn, a botany professor at Gottingen University in Germany who is credited with introducing them to European gardens in the 1750s.

Careful breeding by French and American horticulturists has resulted in giant, dahlia, cactus, pompom, mini, button and cut flower forms of zinnias in a multitude of vibrant colours.

Uses for zinnia

Zinnia is a versatile annual with a range of heights and flower forms. It can be easily grown in pots and containers, mass planted in borders, for cut flowers or as edging around garden beds. Zinnia will usually flower from summer through to autumn, or until the first frosts arrive, and is perfect for planting with fruits and vegetables to encourage beneficial insects, including pollinators.

How to plant and grow zinnia

Climate 

Zinnia is best grown in a warm sunny spot during the warmer summer months, but they can take light shade in the hot summers of warm temperate-climate gardens. Zinnia will not perform in areas with cool, cloudy and moist summers. 

Soil

Zinnia will grow best in moist, fertile, well-drained garden soils but it can withstand periods of dryness or drought once established. Prepare the soil by digging in some aged compost or well-rotted cow manure before planting to improve drainage, moisture retention and plant growth. Most soils with a pH between 5.5–7.5 are suitable – this can be easily monitored with a pH kit. 

In pots or containers use a premium standard potting mix, and water your zinnia at least twice a week during late spring and summer.

How to grow zinnia from seed

• Most varieties of zinnia are usually grown from seed in mid- to late-spring, and treated as annuals. 
• Zinnia resents disturbance to its root system, so seed can be sown into individual cells or pots during spring, and then transplanted into their garden position in late spring or early summer. 
• Alternatively, sow directly into their garden position from mid-spring onwards, or early summer in colder areas. This avoids transplant shock, and the plants tend to grow more quickly. 
• After flowering, remember to collect some of the seed for sowing next year, as most varieties will come true to type.

Caring for zinnia

When planting zinnia, apply a controlled-release organic fertiliser around the plant roots. Liquid feed fortnightly from late spring onwards with a fertiliser high in potash for flowering plants.

How and when to prune zinnia

Deadhead your zinnia regularly to remove spent flowers and to encourage further blooms. The frequent cutting of blooms for indoor decoration will also help to keep your plant flowering prolifically. 

Diseases and pests affecting zinnia

Zinnia is usually trouble free but can occasionally be prone to mildew. Always grow it in a warm sunny spot and remove any infected leaves at the first sign of attack. Thoroughly spray the rest of the plant with a copper-based fungicide. Many of the newer varieties and selections offer more resistance to mildew. Slugs and snails may cause damage to young plants or seedlings in moist soils. Iron chelate-based snail pellets are effective in their control and are the safest to use in the home garden for your pets and the local wildlife.  

If you like this then try

Chrysanthemum: colourful perennial with lobed foliage and masses of intricate daisy-like flowers in all types of shapes and sizes.

Marigold: golden yellow and orange-flowered bedding or edging plant that provides sunny shades of colour in the garden.

Canna: striking perennial producing colourful and luxuriant foliage with tall spikes of lily-like flowers during the warmer months.

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