What Happens if You Trim Zinnias Back?


Zinnias are a flower that can be grown in every garden since they come in a variety of heights and bloom shapes, and they come in brilliant, candy-colored varieties. These annual flowers bloom all summer long with very little maintenance and come in a wide range of sizes, from the semidouble-flowered, 6-inch-tall “Thumbelina” to the speckled, double-petaled, 18- to 24-inch “Candy Cane,” as well as varieties that reach heights of 3 to 4 feet and have pointed tips and cactus-like flowers. Even though the quantity of pruning that must be done in order to maintain continuous bloom differs from cultivar to cultivar, gardeners should not be afraid to trim back any kind of zinnia.

Understanding Zinnia Culture

Zinnias, also known as Zinnia elegans and Zinnia angustifolia, are often sold as spring transplants at garden centres; however, they do not like having their roots messed with. When there is no longer a risk of frost, gardeners in temperate regions with extended growing seasons may plant seeds in soil that drains well a quarter of an inch deep. They flourish in the reflected heat from south-facing walls or along roadways, so be sure to plant them in your garden’s hottest microclimate that gets full light.

If you want to get a head start on the season, put zinnia seeds in peat pots four to five weeks before the last frost. Then, when temperatures are regularly above 50 degrees Fahrenheit, plant the tiny pots straight in the soil without disturbing the roots. When the temperature reaches 70 degrees Fahrenheit, growth then begins in earnest. When the baby zinnias reach approximately 4 inches in height, give them a quarter-strength application of high-phosphorus fertiliser and give them an inch and a half of water each week while they are establishing themselves.

Pinching Zinnias for Fuller Blooms

When you want your zinnias to be as big and bushy as possible, pinch off one inch of the developing tips of the plant as it gets established and development increases. This should be done regardless of whether you plant a short or tall kind. When the plant is squeezed in certain places, it produces branches there. Starting while the plant is still young ensures that the branching will occur lower in the plant, where it will be better able to sustain the extra development as well as the flowers.

Deadheading Zinnia Flowers

Zinnia blossoms result in a substantial volume of seed production. Growers are encouraged by the Michigan State University Extension to prune back the spent blooms early in the season. This will redirect the plant’s energy into creating further blossoms rather than setting seed for the next season. It is not necessary to wait until the blossoms have become wilted before cutting them. Especially cultivars with longer stems provide beautiful blooms for cutting.

When you are deadheading flowers or cutting new ones, trim back to just above a bud or leaf node — a little swelling between a leaf and the stem — to stimulate additional blooms on the same stem. This may be done by cutting back to just above a bud or leaf node. If you wish to have seed for the following year, you should let some of the flowers die and go to seed towards the conclusion of the growing season.

Trimming Plant Leaves

The propensity of zinnia cultivars to acquire powdery mildew, a fungal disease that causes plants to appear grey and wilted, is one of the most significant drawbacks of these types of zinnia. Even though there are cultivars of zinnias that have been developed to be resistant to mildew, such as “Zowie Yellow Flame” and named cultivars of the “Crystal” and “Profusion” kinds, damaged zinnias may still be kept healthy with little selective pruning.

The publication Fine Gardening suggests using your fingers or scissors to remove and dispose of leaves that have developed a chalky grey colour and a drooping appearance. Zinnias should only get water at the soil level, and mulch should be used around the base of the plants to prevent water from reaching the leaves. This will help to prevent powdery mildew from developing on the plants.