To encourage your zinnia to produce more flowers, it’s a good idea to prune and deadhead the plant. Once your zinnia is about 8 to 12 inches tall, cut off the top 4 inches of the stem. This encourages the plants to produce more stems and more blooms. I also deadhead wilting zinnia blooms during the season to make way for new flowers. As annuals, zinnias die back in the winter and won’t need cutting back.
Is Cutting Back and Deadheading Zinnia Flowers Necessary?
In my experience, zinnias are some of the easiest flowers to grow and come in a wide range of colorful cultivars. They are extremely prolific flowering annuals as long as they get plenty of sunlight, regular watering in well-draining soil, and fertilizing. As such, cutting back and deadheading zinnia flowers isn’t strictly necessary.
However, if you do decide to cut zinnias back, I find that you’ll get a bigger bounty of blooms. Zinnias are popular and symbolic cut flowers, so adopting a cut-and-come-again approach means you can harvest them for long periods (and dry and preserve them for even longer). Once you take a zinnia cutting, the plant will redirect its energy to produce new flowers.
If you want the best possible zinnia crop, you can cut back the tops of young plants. This encourages the plant to produce several new stems that will each develop into fabulous flowers. It’s best to do this before the plant begins to flower to maximize the dazzling display.
Zinnias produce large, beautiful flowers in various colors, from pink, purple, orange, red, green, and white. However, old flowers will start to wilt or turn brown. So, if you want your zinnias to look their best, deadheading them is necessary. Deadheading these spent blooms makes the other healthy flowers look even better.
At the end of the flowering season, zinnias will start to die off once exposed to frost. Zinnias are annuals, meaning each plant only lasts one year. Unlike perennials, you won’t have to cut back after the season ends to prepare them for next year.
Before you start pruning or deadheading your zinnias, it’s important to sterilize your gardening tools. Whenever you cut a plant, the fresh cut is vulnerable to common zinnia diseases and pests that can be transferred from other plants. Sterilize your pruning shears and other tools with a 5% bleach solution to avoid this problem.
It’s also crucial to ensure that your shears or scissors are sharp. This ensures the cut will be clean, reducing the risk of diseases or pests attacking. Use a sharpening stone to keep your pruning shears or secateurs in good condition.
Although pruning and deadheading benefit zinnias, it’s essential not to immediately remove too much of the plant. Cutting back too much weakens the plant, impairing its ability to produce flowers. Never simultaneously remove more than a third or a quarter of the total number of stems.
When to Cut Back Zinnias
For the best results, I prune zinnias when they’re relatively young and before they start flowering. The plant should have reached 8 to 12 inches in height before considering pruning it. Each plant should have at least two sets of leaves, and the stem should feel firm. If the stem still feels soft, wait a few more days before trying again.
Removing the tops of the plants at this stage is called “pinching.” This stimulates bushier growth as the plant produces multiple stems from the cut. Each of these stems will go on to produce a beautiful flower.
When to Deadhead
Zinnias usually bloom from early summer until the first frost of fall. Deadheading throughout the season helps your zinnia produce as many flowers as possible before fall. Once a flower has started to wilt or turn brown, snip it off to help the plant concentrate on young buds.
How to Prune
Pinching, pruning, and deadheading are the three main ways of cutting back zinnias. Each method serves a particular purpose and needs to be done at certain times during the season. When harvesting your flowers, cutting them correctly also helps promote more blooms.
Pinching stimulates a plant to produce more stems and should be done when the plant is young. Once your zinnia has reached a height between 8 and 12 inches, it can be pinched. Ensure the stem feels firm and has at least two sets of leaves. If the stem isn’t firm, hold off on pinching for a few days until the stem feels stronger.
I cut the top 4 inches off the young plant using clean, sharp shears or scissors. Although this may seem counter-intuitive, the plant will respond by producing multiple new stems from the cut. This creates a bushier zinnia plant that will yield gorgeous flowers throughout the season.
You may need to prune your zinnias throughout various stages of the season. Pruning is usually only necessary if your plants have become infected with diseases or pests. Using sharp, clean tools, I cut off infected stems, leaves, or flowers to prevent the problem from spreading.
Although zinnias produce beautiful, showy flowers, these blooms will deteriorate over time. Once they start wilting or turning brown, you can deadhead them. I find that this helps my zinnias produce fresh flowers from younger buds while maintaining the beauty of the plant.
Interestingly, you can use deadheading to control the size of your zinnias. If you want a more compact zinnia, I snip off more of the stem when you deadhead a spent flower. The stem will then grow closer to the ground.
If you want to keep the height of your zinnia, remove less of the stem whenever your deadhead wilted blooms. As the plant recovers, new flowers will appear higher on the stem.
When it’s time to harvest cut flowers from your zinnia, cutting in the right place encourages more flowers to develop. Choose a firm flower stem that’s branched off from the main plant. Cut the stem as close to the joint with the main plant, just above a set of leaves.
Using this method allows your zinnia to produce another flower instead of the stem you harvested. This cut-and-come-again ability is a big reason why they make excellent cut flowers.
Unlike perennials, annuals like zinnias don’t need cutting back at the end of the season. Instead, annuals die back naturally once the season ends because they only last a year. Once your zinnias have finished flowering, leave the last flower heads on the plant and collect the seeds. You can then use the seeds to grow next year’s crop.
With the proper care and attention, zinnias can provide a huge crop of fabulous cut flowers. To get as many flower stems as possible, pinch your zinnias once they reach 8 to 12 inches tall. Deadhead any spent flowers throughout the zinnia flowering season to encourage new blooms. Always use clean, sharp tools and only cut stems that feel nice and firm.
For more, see our in-depth guide on how to grow zinnias in pots and containers.