Zinnias are genuinely some of our favorite flowers to plant each year. These annual plants are among the easiest flowers to grow from seed, and provide a variety of benefits in the garden.
If you’re new to growing zinnia flowers, it is very helpful to understand the full life cycle of the plant. Thankfully, in this case, it’s very simple. So, in this article, I’ll go through the zinnia growth stages, from seedling to blooms and beyond. Let’s get into it!
1. Seedling Stage
Like all plants, zinnias start their life as a small seedling. Things move quickly for zinnias, since the seeds can sprout in as little as 3-4 days. The young plants also grow quickly under bright light.
The first set of leaves, called cotyledons, are typically broad and rounded. This allows the young zinnias to capture lots of energy from sunlight. The result: quick growth from a young age.
After about 2 weeks, zinnia plants should have 2-3 sets of “true” leaves. These are the plant’s natural leaf shape that form after the cotyledons.
We typically plant zinnias in small 6-cell trays. After a few weeks, they need to be transplanted into large pots to continue growing. Zinnias can be direct sown, but they are vulnerable to rabbits and other animals during the seedling stage.
2. Growth Stage + Pinching
When warm weather arrives in mid-spring, zinnias are ready to move outside permanently. During this time, the plants continue to grow larger and stronger. The plants will focus on growing a strong root system, a thick main stem, and lots of branches.
If you have grown your seedlings indoors, you may need to harden off the plants. This is the process of slowly transition the plants into direct sun. Make sure you do this gradually over the span of 1-2 weeks to avoid burning the leaves.
About 4-6 weeks after sowing seeds, you have a choice to make: to pinch or not to pinch? Many gardeners choose to pinch out the top of the plant. This forces the plant to grow more side growth, leading to more branches and ultimately more flowers.
Pinching also causes the plants to be slightly shorter, and more bushy. It can be painful to prune zinnias, but I would recommend it for the benefits it brings later on.
3. Flowering Stage
Finally, after weeks of waiting, zinnias begin to put on their show. Each plant can produce dozens of big, colorful blooms. Zinnias are also among the longest-blooming flowers, easily blooming for 10+ continuous weeks!
At this point, the main goal is to keep the plants flowering continually, and to enjoy the vibrant colors. You may also want to keep an eye out for early signs of common zinnia diseases. These include powdery mildew, blight, and bacterial leaf spot.
To help avoid disease, zinnias benefit from proper plant spacing to improve airflow. Also, avoid watering over the tops of the leaves, which can cause fungal diseases to spread more quickly.
Healthy zinnia plants should have continual colorful blooms right up until the first fall frost. These flowers are known to attract beneficial insects, making zinnias amazing companion plants for the veggie garden!
4. Deadheading Stage + Seed Saving
As your zinnia plants mature, older flowers will begin to die back. After a flower loses its color, it begins to mature the seeds in the flower head. Once mature and dried, it is easy to save zinnia seeds for planting next year.
However, just because some flowers are dying doesn’t mean your zinnias are done blooming! I highly recommend deadheading zinnias (removing the older, tired blooms) to encourage more flowers.
Once a flower becomes unsightly, pinch it off a few inches below the bloom. This redirects energy in the plant towards producing more stems and flowers, extending the blooming period.
Zinnia Growing Tips
While zinnias are super easy to grow from seed, I have a few tips to make the process smooth.
- Plant the right varieties. Zinnias come in many forms, including dwarf plants (8-12″ tall) and super tall varieties (4 feet or taller). If you’re looking for cut flowers, you should grow taller varieties. Dwarf plants are great for border edges or companion planting around the base of larger vegetables.
- Avoid frost early on. Zinnias will not tolerate frost very well. So, make sure to transplant only after the danger of frost has passed. This is usually about 2-3 weeks after the local last frost date in your region.
- Poor soil quality. Zinnias can tolerate moderate to low fertility in the soil. There is no need to go crazy amending the soil with pounds of fertilizer for your zinnias. A light feeding can help if your soil is completely depleted, but don’t go overboard with the nutrients.
- Water in the evening. When watering, try to do so in the evening, around sunset. This will allow time for the water to be taken up by the plant, and remain in the soil longer. Also, mulching helps with water retention and weed suppression.
- Get the best vase life. The average cut zinnia flower will have a vase life of about 1 week. To extend this a bit longer, wait for the flower stems to stiffen a bit before cutting. Also, cut the flowers down low, deep into the plant, and always use fresh water for your vase.
I hope this guide to the zinnia plant stages helps you know what to expect from your plants! Knowing the life cycle of your plants before planting is a great way to prepare for a successful flower garden. Good luck!
