With their colorful, vibrant flowers and rich symbolism, zinnias are great at creating a scintillating summer display. These annuals grow in clumps of varying heights, so there are plenty of choices available. Shorter varieties are great in containers, while taller cultivars work well in garden borders. Whichever zinnia you choose, give it plenty of space, and it’ll thrive. In this article, we’ll run through everything you need to know about how tall and wide zinnias grow so you can plan accordingly in your garden.
How Tall and Wide Do Zinnias Grow – The Essentials
Most zinnia varieties grow between 1 and 4 feet tall. Zinnias grow in clumps that usually grow 1 to 2 feet wide. If you’re tight on space, dwarf varieties grow between 6 and 12 inches tall and wide. To help zinnias reach their full height, give plenty of sun and regular doses of water and fertilizer.
|Scientific Name:||Zinnia spp.|
|Native Range:||Mexico, Southwestern United States, parts of Central and South America|
|Growing Zones:||USDA Zones 2 to 11|
|Botanical Characteristics:||Composite flowers that can be single, double, or semi-double, growing on stems ranging from 1 to 4 feet tall|
|Flowering Season:||Zinnias flower from early summer until the first fall frosts|
|Colors:||pink, purple, orange, red, green, and white|
|Watering:||Once a week|
|Soil Conditions:||Fertile, well-draining soils such as loam or clay|
|Fertilizer:||Feed once every 1 or 2 months for the best possible flowers|
|Diseases and Pests:||Alternaria blight, aster yellows, powdery mildew, aphids, broad mites, spider mites, whiteflies|
|Toxicity:||Non-toxic to humans, pets, and other animals|
How Tall and Wide Do Zinnias Grow?
Most zinnia plants will grow between 1 and 4 feet tall and approximately 1 to 2 feet wide. The stems bear individual composite flower heads that can be single, double, or semi-double. Each flower head can be up to 5 or 6 inches wide, depending on the variety.
Zinnias mainly grow in clumps but can also grow as shrubs or sub-shrubs. Depending on the conditions in your garden, taller types of zinnias may need staking. This helps them avoid getting damaged by strong winds and adverse weather conditions.
You can also get dwarf varieties of zinnias that reach between 6 and 12 inches in height and width. These smaller cultivars are ideal for growing in containers and pots. This helps you add some colorful interest to small outdoor spaces such as balconies or courtyards.
Which Zinnias Are Tallest and Shortest?
The tallest zinnias tend to be members of the Benary’s Giant Series. These impressive zinnias routinely grow as high as 4 feet in clumps that can reach 2 or 3 feet wide. Varieties include ‘Benary’s Giant Salmon Rose’ and ‘Benary’s Giant Purple’.
Zinnia elegans ‘Thumbelina’ is the smallest variety of zinnia. These charming little annuals grow as small as 6 inches tall but can reach up to 12 inches. ‘Thumbelina’ zinnias grow in clumps up to 10 inches wide and produce colorful semi-double flowers.
Growth Expectations for Different Types of Zinnias
Although there are hundreds of zinnia cultivars, most of them originate from three main zinnia species. These are Zinnia elegans, Zinnia angustifolia, and Zinnia haageana. Let’s examine the growth expectations for these three different zinnia species:
Zinnia elegans – Common Zinnia
Zinnia elegans is the most common zinnia species and has been used by horticulturalists to breed hundreds of new cultivars. Zinnia elegans grows between 1 and 3 feet tall and can spread up to 12 inches wide.
Originally native to Mexico, this species has also spread to parts of the United States and Central and South America. Zinnia elegans flowers from early summer until fall. Each flower is single and can grow up to 2 inches wide.
Zinnia angustifolia – Narrowleaf Zinnia
Zinnia angustifolia has produced some of the most popular zinnia cultivars. It’s often hybridized with Zinnia elegans to create varieties like the Profusion Series. Zinnia angustifolia grows up to 1.5 feet tall and approximately 1 foot wide.
Narrowleaf zinnias are native to parts of Mexico and the Southwestern United States. This species produces white or yellow single blooms and flowers from early summer until fall. Zinnia ‘Crystal White’ and members of the Star Series originate from Zinnia angustifolia.
Zinnia haageana – Mexican Zinnia
Zinnia haageana, also called Mexican zinnia, typically reaches up to 2 feet tall and 1 foot wide. This species has small single flowers that measure approximately 1 inch across. Zinnia haageana is native to Mexico.
Zinnia haageana has been used to create stunning zinnia cultivars such as ‘Aztec Orange’ and ‘Old Mexico’. These cultivars range in height from 1 to 2 feet. Some, such as ‘Persian Carpet’, have showy double flowers.
Factors Contributing to the Size of Zinnias
Zinnias are relatively low-maintenance plants, but with some effort, you can quickly help them reach their full size. Strong, healthy zinnias can produce a vast crop of blooms that are ideal for cut flowers or dried floral arrangements. Here are a few factors that contribute to the size of your zinnias.
Giving your zinnias the best possible growing conditions will help them grow as tall as possible. Zinnias aren’t particularly fussy, but they do need 6 to 8 hours of full sun every day. This helps them produce the necessary vital sugars for impressive growth.
Zinnias should be watered about once a week or whenever the top 2 inches of soil feels dry. To reduce the risk of zinnia diseases and pests, water at the base of the stems. Avoid splashing water on the foliage, as this can lead to rot.
The best position for zinnias is a south or southwest-facing sheltered spot. This helps your zinnias get plenty of sun while also protecting them from strong winds. If you’re growing a tall variety, it’s worth staking the plant to give it some extra support.
Fertilizer and Nutrients
To produce the best and brightest flowers, zinnias need lots of nutrients. Providing adequate nutrition also helps your zinnias grow as tall as possible. These nutrients should come from the soil and can be topped up with fertilizer.
Zinnias need well-draining soil that’s still fertile, so aim for loamy soils wherever possible. Chalky, sandy, and clay soils also work, but you may need to add some organic matter for extra nutrition. Once flowers start to emerge, fertilize your zinnias once every month or two to provide the necessary nutrients. Always dilute your fertilizer according to the instructions on the packet.
If you want your zinnias to be tall and healthy, you must give them space. If zinnias are too crowded, it can hamper their growth and leave them vulnerable to diseases and pests. Plenty of space promotes good airflow, reducing the risk of disease.
Once zinnia seedlings emerge, thin them out so that there are approximately 12 inches between each plant. If you have zinnias that grow over 2 feet tall, they’ll need more space. Provide about 18 inches of space between taller zinnia varieties.
Although zinnias don’t technically need pruning, it can be beneficial if you want bushier plants that produce more flowers. Cutting the top off a young zinnia plant encourages it to create more stems, which will eventually yield more flowers. This is known as “pinching.”
Wait until your zinnias are between 8 and 12 inches tall and have at least two sets of leaves. Check that the stems feel firm and leave them for a few more days if they feel soft. Cut off the top 4 inches of the stem, just above a set of leaves.
Zinnias that have been pinched will grow into bushier plants that spread pretty wide. Pinched plants produce a more significant crop of flowers, making them ideal for a cut-and-come-again approach.
Diseases and Pests
Zinnias suffering from diseases or pests won’t grow as tall as healthy specimens. Most common zinnia diseases or pest infestations cause weak, stunted growth. Pests such as aphids and whiteflies feed on zinnia sap, depriving the plants of the vital sugars they need to fuel growth.
The best way to avoid pests and diseases is to ensure that your zinnias receive the correct growing conditions. Keep plants appropriately spaced to minimize the risk of spreading disease. If you spot diseases or pests, use methods such as horticultural oils, insecticidal soap, and organic fungicides to treat the problem.
Cultivating a tall, healthy crop of zinnias adds plenty of interest to your garden. Tall plants also provide plenty of cut flowers for vases and bouquets. Most zinnia cultivars grow between 1 and 4 feet tall and about 1 to 2 feet wide. Dwarf cultivars grow between 6 and 12 inches tall and wide. To promote tall growth, give your zinnias the conditions they need to thrive and pinch young plants.
For more, see our in-depth guide on how to grow zinnias in pots and containers.