After zinnias flower, cut off the old flowers (a process called “deadheading”) to encourage more flowers to form. Zinnias are annuals and will die with the first hard frost of fall. If you want them to reseed, let the last flowers of the season mature fully and scatter their seeds.
If you planted annual wildflowers like Cosmos, Zinnias, or Sunflowers, leaving them up through the winter helps them to drop their seeds and come back the next year. If you can't stand leaving them up (or are part of an HOA that makes you cut them back), cut them back and leave the debris on the ground.
Zinnias need to be picked when they are fully ripe, otherwise they won't last in the vase. To tell whether a zinnia is ready to harvest, use the “wiggle test.” Simply grab the stem about 8 inches (20 cm) down from the flower head and gently shake it. If the stem is droopy or bends, it is not ready to cut.
Zinnia will die if it freezes and must be pulled out and thrown to the compost after the first frost spells.
A few start to suffer when temperatures drop below 40. So get them inside in the next couple of weeks. True annuals such as vinca, zinnias and marigolds are eventually going to croak even if you try to milk them through winter.
Do zinnias come back every year? No, zinnias don't come back every year as they are annual plants. This means that the flowers complete their entire life cycle in one year. Zinnias are very vulnerable to frosts and will die soon after the first frost.
By repeatedly deadheading zinnias throughout the summer, you can keep plants in the flowering stage, provide long-lasting color. Deadheading also keeps plants looking their best. Most flowers lose their attraction as they fade, leaving an unsightly brown head behind.
Once your zinnia is about 8 to 12 inches tall, cut off the top 4 inches of the stem. This encourages the zinnia to produce more stems and more blooms. 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.
So the short answer is yes! Scatter those seeds or space them. It's truly up to you and the look you are going for. The zinnias will still do their thing.
Unlike perennials, annuals do not come back from season to season so there is no reason to leave these in the ground. Pull them up, roots and all, and add them to your compost pile. Remove weeds and leaf debris. These are common places for diseases and pests over winter.
Photo by: Unverdorben Jr / Shutterstock. One of the easiest annuals to grow, zinnia flowers bring an explosion of color wherever they go. The show lasts from late spring until the first frost in fall.
Also, do not cut back hardy perennials like garden mums (Chrysanthemum spp.), anise hyssop (Agastache foeniculum), red-hot poker (Kniphofia uvaria), and Montauk daisy (Nipponanthemum nipponicum). Leave the foliage. It's important to protect the root crowns over winter.
Zinnias are annuals that have a long flowering season. The zinnia season usually lasts from early summer until fall. Once the first frosts arrive in late September or early October, zinnias will deteriorate rapidly. Some zinnia cultivars may start blooming in late spring and continue until fall.
Some zinnias grow tall and top-heavy and get toppled over by the wind. To protect them, many growers either use stakes to support their plants, or, if growing many flowers, place horticultural flower netting across the entire bed. While not invisible, the netting does a good job supporting all those heavy flowerheads.
If zinnias are allowed to flower and set seed and the seeds drop to the soil, then there is a good chance that the seeds will germinate and grow the following spring. There is no guarantee that it will happen, but this is one of the main reasons why these flowers are loved by so many gardeners.
Pinching your flowers back encourages the plant to branch out and produce more blooms. Zinnias are cut-and-come-again plants, so the more you cut from them, the more they'll produce for you.
Once the zinnia plants begin to bloom, they will continue to produce flowers all season long, right up until the first frost of late fall. Each mature zinnia stem can bloom for several weeks before becoming spent.
Zinnias are a “cut and come again” flower, so when you cut the plant “hard,” it responds by sending out even more long, strong stems all season long. We cut zinnias directly into fresh clean water with a drop of chlorine or a CVBn pill added to the water.
Zinnia seeds can be saved from all varieties to grow on the next year, however not all types will grow true to type. 'Select varieties that have been open pollinated, as opposed to hybrids – which can vary widely in the next generation – and preferably organic so as not to harm bees,' says Clapp.
I pinch any zinnias that are expected to grow around 18-inches or taller and tend to be tall and leggy. The zinnia in the photo (above) is a prime candidate for pinching. I'll show you (below) how it changed after it was pinched back. No matter what, I'd encourage you to try it and see what happens.
If planting zinnias in the same place you grew them last year, chances are they could have dropped seed. If you did let last year's zinnias dry out, then you may have volunteers popping up.
Zinnia seeds remain viable for 3 to 5 years.
Zinnias flower all summer and often into fall, lasting in the garden from two to five months. Zinnias are most robust during the hot summer and the warmest spring and autumn months. Zinnias don't need to be deadheaded, but your plants may have a longer bloom period if you do.