Once you know these zinnia growing tips, you can enjoy these sun-loving flowers from first bloom to fall frosts. Provide rich soil, keep up with the watering, and protect those tall stems with supports.
And, be sure to learn how to pinch your stems for bushier plants and more flowers.
Getting Started With Zinnias
There are so many gorgeous zinnias available that once you grow some, you’ll want more.
For those of us in cold climates, zinnias can provide flowers from first bloom throughout the summer, only slowing down once the weather starts to cool off
While you can buy perfectly good zinnias as bedding plants at nurseries, I highly encourage browsing through your favorite seed catalogs to discover a whole world of possibilities. There are far more options available from seed than plant shops can provide.
Before we dive into the top growing tips, it’s good to know what zinnias are all about.
Many Flower Types
One of the first things you’ll notice is the flower formations. They come in single, double, and semi-double flowers ranging in diameter from small to large. These can be on single or multiple stems, in heights ranging from inches like Zinderellas to Benary’s at several feet tall.
As enchanted as I am with the double, fluffy, dahlia-like blooms of some zinnias, they may not be pollinator-friendly. The Trouble With Double Flowers explains why this can be a problem.
If you are aiming for a more pollinator-friendly garden, look for simpler, single, daisy-like zinnias with accessible nectar and petals the bees and butterflies can land on. Suggested varieties include Zinnia ‘Lilliput’, an heirloom variety from the 1870s, and Zinnia ‘Zowie’, a long-blooming butterfly magnet.
Some of us love zinnias for those vivid colors that look like something out of Candyland. Others swoon over the pastels that come in so many color values, collectively creating an elegant work of art in the garden. If you want to see what I mean, have a look at these zinnias at Floret Flower Farm. Just gorgeous!
Looking through the catalogs I’m pretty sure you can find zinnias in every color except blue. Imagine growing swaths of them with favorite color themes. Delightful.
Deadheading Versus Pruning
Deadheading is the removal of flowers and their stems. This is done after peak bloom time to prevent seed production and/or encourage new blooms.
Pruning is the removal of cutting back of stems or branches on shrubs, vines, and trees. We prune to remove dead, damaged, diseased, or crowded branches to improve the overall health or appearance.
Seed Saving & Propagation
It takes just minutes to learn to grow zinnias from cuttings to propagate more plants all season long.
And, come harvest time, save your seeds for sowing again next year.
7 Best Tips For Growing Zinnias
1Grow In Full Sun
If you want to get maximum bloom time from your zinnias, grow in full sun. And by full sun I mean six hours a day minimum, but the more, the better. It doesn’t have to be six continuous hours—periods of full sun adding up to this amount (or more) is fine too.
This explains terms like full sun, part sun, part shade, and shade and gives tips for assessing the light conditions in your garden.
I’ve tried growing zinnias in various light conditions in my garden and hands-down the flowers come sooner and grow bigger in relation to how much sunlight they are getting.
Other key growing conditions like fertile soil amended with compost, consistent moisture, and protection from the wind are important too, of course, but be sure to give them lots of sun and you’ll see them at their best.
2Sow Seeds Directly Outdoors
For some of us with shorter growing seasons the timing doesn’t work out, but if you can, sow your zinnias directly outdoors after the risk of frost has passed.
This is possible if the growth cycle (days to maturity) of your zinnia fits within the number of frost-free days in your growing season.
The ideal soil temperature range for germination is 80-85°F (27-29°C), but that’s just for rapid sprouting. Soil temperatures of 70-75°F (21-24°C) work for both germinating and growing.
There are more zinnia growing tips here.
Why sow directly?
So many gardeners notice how their zinnias can sulk after transplanting. They don’t like their roots disturbed and the change can set them back. Related to this, they also do not like being rootbound, which can happen when sowing in small containers.
I would never give up zinnia growing if indoor sowing was my only option, but just know that direct sowing outdoors may be more successful. Plus, if it’s an option, it’s easier.
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.
The most important tip is to get any supports or trellis you use in place while the plants are young so they can grow into them. If you wait, you risk damaging the plants trying to coax them into place.
Some of the most popular tall, showy zinnias are the Benary’s Giant Series which can grow 4 to 5-feet tall.
4Pinch Your Plants
It’s funny how many people associate pinching with zinnias even if they are not sure what it is.
Pinching is a simple form of pruning where we selectively remove some stem tips, causing the plant to grow additional stems. And for zinnias this means you also get more flowers.
It’s completely optional but definitely benefits some plants when the goal is flowers—and more flowers.
Use this tutorial on How to Pinch Zinnias for step-by-step instructions.
The term “deadhead” means to remove old flowers and their stems.
Zinnias start flowering approximately 7 to 8 weeks after germination and they are what we call “cut and come again”. This means, you can pinch and deadhead and they keep producing.
The idea is that the plant will put its energy into more growth instead of seed production.
If you also want to save seeds, leave your best flowers to turn to seed.
Tip #7 has more on seed saving.
6Root Your Cuttings
Good news! With all this pinching and deadheading going on, you’ve got stem cuttings that you can use to propagate more plants.
Zinnias are excellent for growing from stem cuttings.
The key point to know is that zinnias can grow roots from their leaf nodes—that area on the stem where the leaves grow from. The detail to pay attention to is, when we pinch back stems to encourage branching, we leave the nodes in place. For cuttings, you need to be sure you have some nodes on your cut stem.
This shows you how to root zinnia cuttings.
7Save Your Best Seeds For Next Year
One of the most important tips to know about seed saving is your best flowers have the best genetics and make the best seeds.
Avid seed savers take time during the growing season to mark their favorite flowers and fruit so they know which plants to choose for seed harvesting in fall. It’s not so easy to tell which ones were show-stoppers once the flowers have faded.
And, even within the same plant, there can be quite a variation in bloom quality.
If you have a zinnia with many flowers, place strands of ribbon around your favorite stems as markers for seed saving time.
Keep in mind that while some zinnias are grown from open-pollinated seed that grow true generation after generation, most of the seeds we buy in catalogs are F1 hybrids.
The seeds from hybrids likely won’t grow true to the parent, but you will still get some sort of wonderful zinnia blooms from their seeds.
Also, some seeds are protected by plant patents, so check the details on your seed packet to know what you’ve got.
If you are determined to grow a specific type or colors, stick to growing from F1 seeds.
Zinnia | Genus: Zinnia | Asteraceae family
Frost-sensitive flowering annuals native to Southwestern U.S., Mexico, and South America
Tips for Growing in Cold Climates (Hardiness Zones 4 to 8): Zinnia Growing Tips
- Popular Species | Zinnia elegans, Z. angustifolia, Z. haageana, Z. marylandica
- Sun: full sun 6+ hours or more each day.
- Soil: fertile soil, rich in compost.
- Propagation: seed, cuttings.
- Seeds: open-pollinated or F1 hybrids.
- Seed to Maturity: 60 to 80 days.
- Flowers After Germination: 7 to 8 weeks.
- Start indoors: 4 to 6 weeks before last frost. Keep grow lights 3-inches above seedlings for 16-hours per day.
- Sow Outdoors: after last frost, soil 60°F (16°C), up to 85°F (29°C) is ideal.
- Sowing Depth: 1/4-inch, keep soil moist during germination.
- Spacing: check your seed packet. Varies between 9 to 24-inches apart.
- Germination: 5 to 10 days.
- Flowers: mid-summer through to fall frosts.
- Sizes: 6 to 10-inches tall, flowers 2 to 6-inches in diameter.
- Colors: everything but blue.
- Container Growing: small or dwarf varieties.
- Care: pinch and deadhead for fuller plants and more flowers.
- Water: thirsty during germination and early growth. More drought tolerant later on.
- Pollinators: single, maybe not double flowers. Bees, hummingbirds, butterflies, hummingbird moths
- Pests: aphids, caterpillars, earwigs, leafhoppers, Japanese beetles, spider mites, thrips.
- Diseases: Alternaria leaf spot, aster yellows, bacterial leaf spot, botrytis, powdery mildew, root, stem, and crown rots (caused by fungi).
Shop Online: Buy zinnia seeds | Botanical Interests (US shipping)
I hope this has provide the tips and encouragement you need to start growing zinnias.
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~Melissa the Empress of Dirt ♛