Growth Habit of Zinnias

Types

• The common zinnia (Zinnia elegans) is native to Mexico and is an upright, bushy plant that matures at 24 to 30 inches tall and about 12 inches wide. The narrowleaf zinnia (Z. angustifolia) is native to both the American Southwest and Mexico. It too is bushy, but is an intermediate between being fully upright and more mounded. Both of these zinnias are widely available to purchase as seeds in the United States. Hybrids between these two species, such as those in the Profusion series, provide gardeners with a wider range of flower colors and intermediate growth habits.

Cultivars

• Scores of zinnia cultivars exist, with a wide array of flower sizes and colors as well as mature height, spreads and forms. Common zinnias include both upright, tall-growing selections as well as dwarf types that remain small, rounded balls. For example, cultivars in the Sun and Whirligig series are upright bushes 20 to 24 inches tall. Cultivars in the Thumbelina and Peter Pan series of zinnias mature at 6 to 12 inches tall. Narrowleaf zinnia cultivars develop many more thin branches, creating upright to spreading mounds 8 to 15 inches tall but 12 to 20 inches wide.

Pinching and Trimming

• Horticulturists developed various cultivars of zinnia to be naturally bushy and produce lots of flowers. While some zinnias are more upright and tall and others spreading and mounded, gardeners can manipulate the growth habit of the plants by pruning. Pinching removes stem tips, causing buds to sprout at the bases of lower leaves and creating a more multibranched, bushier plant. Deadheading -- the removal of old, spent flowers -- also results in the renewal of leaf and flower stems. Even if pruned, any zinnia will rejuvenate with new growth and still mature to the height and size predisposed by its genes.

Staking

• Dwarf types of common zinnia and narrowleaf zinnia that remain close to the ground aren't heavily affected by winds or torrents of rain. Narrowleaf types may look beaten down, but the return of dry, sunny weather quickly finds the thin stems orienting more upright. Tall-growing, upright common zinnias branch as they age, often becoming somewhat top heavy. Numerous upward and angled branches radiate from the lone stem, catching wind and rain. Upright zinnias benefit from being staked to prevent them from snapping in downpours or being quickly snapped or bent over from gusts of wind.

Insight

• Look at the zinnia seed packet or seedling label to learn the expected height and spread of the plant at maturity and the recommended spacing between plants for best growth. With so many cultivars of zinnia available, do not assume all zinnias attain similar mature sizes and habits.