How to Grow Zinnias

Zinnias thrive in average soil if it is well-drained and in a spot that receives at least 8 hours of full sun each day. If needed, amend the soil with compost or sand to facilitate drainage. Because they are susceptible to powdery mildew, allow for good air circulation and don’t overcrowd.

There are several species of Zinnia. The more common are:

•  Zinnia elegans is among the most popular in today’s gardens. It grows 1 to 3 feet tall with branching stems and large flowers, which range from about an inch to 5 inches. It is available in many colors and cultivars. A few include ‘Benary’s Giant’, which has double flowers in a wide range of colors and grows 3 to 4 feet tall; ‘Zinderella’ with pompon-like, 2-inch flowers in several colors and about 1 ½ to 2 ½ feet tall; ‘Magellan’ with double 4- to 5-inch blooms and 12 inches tall; to the diminutive ‘Thumbelina’, with a 2-inch, semi-double bloom on a plant that grows to about 6 inches tall. 
• Zinnia angustifolia is sometimes called narrow-leaf zinnia, creeping zinnia, or Mexican zinnia. It is low-growing and popular in borders and mass plantings. It is a profuse bloomer through the summer until frost. It grows from 8 to 16 inches tall. Cultivars are available in many colors. A few include ‘Crystal White’, an All-America Selections winner with 1- to 2-inch blooms and growing to about 12 inches tall and ‘Star’ with orange, gold, or white 1- to 2-inch flowers and about 12 inches tall. 
• The Profusion series combines attributes of both the above and are popular hybrids that are used extensively in landscapes and containers. 

Zinnias can be seeded directly into well-worked soil or get a jumpstart by setting out transplants. (See below guidelines on incorporating fertilizer into the soil at the time of planting.) If starting your own transplants, start them in peat pots or biodegradable material to easily plant directly into the garden. This helps avoid disrupting their roots. 

To direct seed, plant outside after frost has passed and when the soil temperature is at least 70 degrees F. Soil thermometers from the garden center are helpful tools to get an accurate reading. Plant seeds ¼ inch deep. Zinnias bloom 8 to 12 weeks (about 3 months) after sowing seeds. Set out transplants when the soil warms to 60 degrees.

Space between plants depends on the growth habit of the plant, such as whether it has a bushier habit or is a tall plant. Tall, singular plants need about 6 inches of spacing while bushier types may need around 18 to 24 inches. 

At the time of planting, water in the seeds or transplants so the soil is evenly moist. As they grow, water when the top 1 to 2 inches of soil are dry. Do not overwater. Water from the base of the plant to help keep the foliage dry and reduce chances of fungal diseases such as powdery mildew. 

If you missed out on seeding in the spring or wish to enjoy this plant through the fall until the first frost, seed by early July to mid-August, depending on your region. 

Fertilizing

• Minnesota Extension recommends a general-purpose fertilizer such as 10-10-10 with equal amounts of nitrogen (N), phosphorus (P), and potassium (K) incorporated into the soil at the time of planting. Follow label directions.
• After planting, fertilize monthly with a fertilizer that is higher in phosphorus content than nitrogen to promote new blooms.

Controlling Pests, Diseases, and Other Problems

• Some zinnias are susceptible to powdery mildew though breeding programs have resulted in many new options that are quite resistant to disease. 
• Zinnia leaf spot is a fungus that usually starts at the base of the plant and works its way up the plant. LSU Extension recommends enjoying the plant before the spots take over or, if necessary, use a fungicide every 7 days. 
• Many zinnias attract pollinators. Penn State Extension recommends interplanting a row of zinnias between rows of vegetables or as a border around vegetables to attract more pollinators to your garden (check plant tag or seed package to make sure your zinnia choice attracts pollinators as some zinnias have had pollen and nectar bred out of them.)

Cut the flowers when the centers are beginning to fully open. Harvest flowers early in the day for cut flower arrangements. 

Deadheading helps them continue to produce blooms. Late in the season, or even throughout the season, leave some seed heads for the birds to enjoy. 

Storing

Zinnias typically last 7 to 12 days (about 1 week 5 days) in a bouquet. Before placing in a vase, remove the lower leaves. Keep them looking their best by changing the water every couple of days to cut down on algae growth. 

Zinnias can be dried. When flowers are at their peak, cut the stems, remove the leaves, and hang upside down out of direct light and in an area with good air circulation. Iowa State Extension recommends that double flowers hold their shapes better than single forms when drying. The colors will change slightly after drying.

• For the greatest impact, plant zinnias in small groups or masses. 
  
• Water at the base of the plant and early in the day to allow any dampness on the foliage to dry. 
• Through the years, certain zinnias have been recognized by the All-America Selections for their amazing performance. Some popular go-getters of the past 20 or so years are the Profusion Series, which grow in a compact, bushy form, typically up to 12 inches tall and wide. They are a cross between Z. elegans (the tall upright form) and Z. angustifolia (the narrow-leaf zinnia). Most recently, in 2021, Profusion Red Yellow Bicolor won the AAS Gold Medal. This little beauty starts the season with a vibrant red center ring surrounded by golden-yellow outer petals. The flowers turn to shades of apricot, salmon, and dusty rose as the season progresses. Selections in the Profusion series are noted for their ability to tolerate heat and humidity, resist disease, and for being easy to maintain. They don’t require deadheading. Aptly named, they are profuse bloomers. Cherry, Orange, White, Red, Deep Salmon, and Hot Cherry are all AAS winners, giving gardeners lots of great options for plants to edge a border with taller plants behind, or to enjoy in containers.
• A few other AAS Winners include Zinnia Queeny Lemon Peach that starts as a bright yellow and changes to a light coral color and is lovely in cutting gardens (the entire Queeny series is sublime). Zinnia Holi Pink F1 is a vibrant pink that doesn’t fade like some zinnias. It is suitable for containers or garden beds. Zinnia Holi Scarlet F1 is vibrant and its deep red flowers are striking. Plant in mass in landscape beds or in containers. Zinnia Zahara Starlight Rose is a stunner with its white flowers and rose stripes or look for a Zahara mix. 
• Have fun with this plant. Try some in containers, some as bedding plants, and others in the cut flower garden.