Zinnias add bright, irresistible bursts of color to the garden during the summer months. These stunningly symbolic flowers are low-maintenance plants that are easy to grow for beginners and experts alike. As annuals, zinnias grow quickly because their entire life cycle only lasts for a single year. In this article, we’ll explain how long zinnias take to flower.
How Long Do Zinnias Take to Flower – The Essentials
Most zinnias cultivars take 40 to 60 days to flower from seed if sown directly into the soil. Starting zinnia seeds indoors and transplanting them out can produce flowers in as little as 30 days. Sow zinnia seeds in late spring once the last frost has gone. Seedlings should emerge in 7 to 10 days.
|Scientific Name:||Zinnia spp.|
|Native Range:||Mexico, Southwestern United States, parts of Central and South America|
|Growing Zones:||USDA Zones 2 to 11|
|Botanical Characteristics:||Composite flowers that can be single, double, or semi-double growing on stems ranging from 1 to 4 feet tall|
|Flowering Season:||Zinnias flower from early summer until the first fall frosts|
|Colors:||Pink, purple, orange, red, yellow, green, white|
|Watering:||Once a week|
|Soil Conditions:||Fertile, well-draining soils such as loam or clay|
|Fertilizer:||Fertilize zinnias every 1 or 2 months for the best possible flowers|
|Diseases and Pests:||Alternaria blight, aster yellows, powdery mildew, aphids, broad mites, spider mites, whiteflies|
|Toxicity:||Zinnias are not considered to be toxic or poisonous to humans, pets, or other animals.|
Zinnias are annuals, which means that each plant only lasts a single year. Annuals need to be sown yearly if you want to keep enjoying them. As such, annuals develop very quickly once the seeds are sown.
Zinnia seeds don’t need to be started off indoors, but this can speed up the flowering process. In most areas, zinnias can be sown directly into the soil where you want the plants to grow. Let’s take a closer look at when, where, and how to plant zinnias.
When to Plant Zinnias
Zinnias should be sown directly into the soil in late spring and early summer. Make sure that all risk of frost has passed before you plant your zinnias because they’re vulnerable to the cold. Check that the soil is warm to help them germinate – approximately 70 to 75ºF is the ideal temperature.
If you buy young zinnia plants or start seeds off indoors, plant them once the soil reaches 60ºF. If your soil is taking a while to warm up, use a cloche or polythene sheet. You can also put down mulches such as straw.
Where to Plant Zinnias
Zinnias need to be sown or planted in a warm, sunny spot, preferably sheltered from the wind. At each stage of their life cycle, zinnias need 6 to 8 hours of full sun every day. South or southwest-facing locations are ideal.
Zinnias also need fertile, well-draining soil to thrive. Most types of soil work well, but loam or clay is ideal. Provide extra nutrients and drainage by mixing some organic matter like compost or manure into the soil.
How to Plant Zinnias
Once your soil is warm and the risk of frost has passed, it’s time to sow your zinnia seeds. Push each seed a ¼ inch deep into the soil and water in well. Ensure the soil is well-draining, so the seeds don’t become waterlogged.
When seedlings emerge, thin out the young plants depending on the mature size of your chosen zinnia. For smaller zinnia varieties, leave 8 to 12 inches of space between each plant. If your zinnia is expected to grow 2 feet tall or above, provide up to 24 inches between each plant.
Alternatively, you can start off your zinnia seeds indoors. In a tray of seed compost, sow the seeds at a depth of ¼ inch. Cover them with a layer of perlite or vermiculite and keep them moist until they emerge. Do this approximately six weeks before the last spring frost is due in your area.
Growth Expectations and Timings
Zinnias emerge reasonably quickly once the seeds have been sown. In approximately 7 to 10 days, you should start to notice seedlings coming up. They need warm soil to germinate quickly, so if your soil is too cold, it will take longer.
Zinnias sown directly into the soil should produce flowers in around 40 to 60 days – about 6 to 8 weeks. Seeds that were started off indoors and transplanted outside should flower more quickly. It can take as little as 30 days for these plants to bloom.
Most species of zinnia will grow between 1 and 4 feet high and up to 2 feet wide. Dwarf varieties stay compact, making them ideal for containers. These cultivars grow between 6 and 12 inches tall and wide in small clumps.
Giving your zinnias the best possible care helps them produce a fantastic crop of bright, beautiful flowers. Zinnias are low-maintenance plants and are incredibly easy annuals to grow. That said, they do have a couple of specific requirements.
Zinnias need plenty of sun to germinate quickly and produce their famous flowers. Give your zinnias 6 to 8 hours of full sun every day. If you can, plant your zinnias in sheltered south or southwest-facing locations to maximize their exposure.
Although they’re drought-tolerant, zinnias still need regular watering to fuel flower growth. Water your zinnias once a week or whenever the top 2 inches of soil are dry. Try to avoid getting water on the leaves and aim for the bottom of the stems. This helps prevent diseases and pests from infecting your zinnias.
Zinnias need fertile, well-draining soils that provide plenty of nutrients without becoming waterlogged. Zinnias also like neutral or slightly acidic soils between 5.5 and 7.5 pH. The best soil types for zinnias are chalky, loamy, sandy, or clay soils.
Incorporating some organic matter into the soil provides extra nutrition and drainage to help your zinnias thrive. If you have dense clay soils, add in some grit and organic matter to improve the drainage. Before you sow or plant zinnias, make sure that the soil temperature has reached 70 to 75ºF.
Adding regular doses of fertilizer helps your zinnias explode with vibrant flowers. During the flowering season, feed your zinnias once every 1 or 2 months. Dilute the fertilizer according to the packet instructions.
If you want the best flowers possible, choose a fertilizer with a higher phosphorus dose. An ideal NPK ratio for zinnias is 5-10-5. Phosphorus is crucial for flower development, especially if you’re using your zinnias as a cut-and-come-again flower crop for vase or bouquet arrangements.
Cutting Back and Deadheading
Cutting back your zinnias isn’t strictly necessary, but some strategic pruning can help you get more flowers (perfect if you’re interested in drying or preserving zinnias as well). When young zinnias are approximately 8 to 12 inches tall and have at least two sets of leaves, you can “pinch” them. This means cutting off the top 4 inches of firm young stems.
Although that sounds strange, it actually stimulates your zinnia to produce multiple stems from the cut. Each of these new stems will create its own flower, doubling your crop. You’ll get a bushy, highly productive zinnia plant if you pinch several stems early in the season.
Throughout the blooming season, older zinnia flowers will start to wilt. Deadheading these spent blooms encourage the plant to focus on emerging buds, which produce more flowers. Ensure that your secateurs or pruning shears are clean, sterile, and sharp before cutting. This minimizes the risk of disease.
Diseases and Pests
Zinnias can suffer from some pests and diseases if they aren’t grown in the right conditions. Diseases like Alternaria blight and powdery mildew and pests like aphids, spider mites, and whiteflies are the most common issues. If a zinnia becomes infected, it will suffer from weak or stunted growth and may struggle to produce flowers.
If you notice symptoms of diseases or pests on your zinnias, don’t worry – there are several solutions. Insecticidal soaps and horticultural oils like neem oil can tackle most pests or diseases. For aphids and other sap-sucking insects, a well-aimed blast from a hose may solve the problem.
You can use organic copper fungicides for fungal problems such as aster yellows. Avoid synthetic pesticides wherever possible, as these can harm beneficial insects like bees and hoverflies.
To prevent diseases and fungal infections, give your zinnias enough space to have good airflow around the plant. Weed the soil regularly and remove any nearby leaf litter. Try not to get the leaves too wet when watering, as this can lead to infections. Instead, water at the bottom of the stems.
Zinnias are fantastic, low-maintenance annuals, so you won’t have to wait long for a spectacular display of flowers. Zinnia seedlings appear in 7 to 10 days. If sown directly outside, zinnias can produce flowers in approximately 40 to 60 days. If you start seeds off indoors, you can get flowers in as little as 30 days.
For more, see our in-depth guide on how to grow zinnias in pots and containers.