How to Grow Zinnias from Seed: A Beginner’s Guide
Zinnias are many gardeners’ favorite flowers thanks to their easy-to-grow nature and repeat blooms. However, they still require proper attention and care! Join flower farmer Briana Yablonski to learn how to grow zinnias from seed.
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If you want to add a splash of color to your landscape or start a cutting garden, zinnias are one of my top recommendations. These annual flowers are easy to grow and provide you with months of fresh flowers that hold well in a vase.
While you can purchase zinnia seedlings from garden centers, these flowers are easy to grow from seed. Nurturing the small seeds into blooming plants provides a sense of satisfaction and wonder, and it allows you to grow unique varieties you may not be able to find at plant nurseries.
Although zinnias are one of the easiest cut flowers to grow, planting from seed can be intimidating, especially if you’re new to gardening! I’m here to tell you that there’s no need to be intimidated. As long as you follow these instructions, you’ll be enjoying a patch of zinnias in a few months.
Select a Variety
This is one of the most fun and challenging parts of growing zinnias! You can choose between dozens of zinnia varieties, so narrowing your selection down to one or two types is no small feat. Although you may want to select a dozen different flowers, I recommend sticking with a few varieties the first time you grow zinnias from seed.
Since zinnias have similar environmental requirements, personal preference is the main factor driving your decision. Do you have a small raised bed or container? Then choose the dwarf ‘Thumbelina.’ Looking for something unique? Check out the double salmon blooms of ‘Senora.’
After you’ve chosen your preferred varieties, purchase the seeds as soon as possible. Popular varieties often sell out early in the year, so grab your seed packets while you can.
Wait Until the Right Time
After you have your seed packets, you may want to wait to plant. Zinnias are frost-sensitive annuals that thrive in warmer weather. Therefore, you should wait until your last frost has passed to sow them outdoors.
Even if you plan to start your seeds indoors, you should wait until a few weeks before your last frost date. These seeds are quick to germinate and mature, so the seedlings will be ready to plant outdoors about four weeks after you sow the seeds. If you start the seeds too soon, you’ll be left with overgrown plants that are itching to get in the ground.
While you can up pot seedlings that have outgrown their containers, this is an unnecessary step. Instead, be patient and wait until frost-free days are just a few weeks away.
Although you shouldn’t plant zinnias until the danger of frost has passed, you can continue sowing the seeds throughout the summer. Since most varieties take between 70-90 days to go from seed to flower, stop sowing seeds about three months before your predicted first fall frost.
Since zinnias continue to produce flowers for multiple months, you don’t need to succession plant every week or two. I like to sow two or three rounds of zinnias so new plants can take over when older plants become diseased or stressed by summer’s heat.
Find and Prepare a Suitable Location
Before you plant zinnias, make sure you have a location that will support their growth. Zinnias require full sun, so look for an area that receives at least eight hours of bright light daily.
You should also make sure the area is free from standing water since these annuals dislike sitting in wet soil. Finally, ensure ample room for the zinnias to expand without encroaching on other plants. Most of these annual flowers grow multiple feet tall and wide, so they will appreciate having lots of space to grow.
Next, check the soil. Zinnias aren’t super picky about soil type, but they won’t thrive in compacted soil. If you find the ground is hard, loosen it with a digging fork or broadfork, then mix in some compost.
You can also grow zinnias in containers if you don’t have a suitable garden area or raised bed. Fill the pots with well-draining potting soil before planting.
Decide Between Direct Sowing or Starting Seeds Indoors
As I mentioned above, you can either sow zinnia seeds directly in the ground or start them in indoor containers. Either option works well, so it’s up to you to weigh the pros and cons of each method and determine which is best.
How to Direct Sow Zinnias
Since zinnias easily germinate outdoors, you can directly sow them in your garden. Wait until the air temperature remains above 50°F (10°C) at night and the soil temperature is at least 60°F (16°C).
Check your seed packet to determine proper plant spacing. Twelve-inch spacing works well for many varieties, but some benefit from closer or wider spacing.
Make a small hole about a quarter of an inch deep in the soil. Place one to two seeds in each hole and cover with a small amount of potting soil. Once the seeds have germinated, thin the seedlings to one plant per hole.
Pros of Direct Sowing
This option eliminates the need to develop an indoor seed-starting setup, which means you don’t have to spend money on seed-starting containers, grow lights, and potting soil. Direct sowing also removes the labor involved with sowing seeds in flats and later transplanting them outdoors.
Cons of Direct Sowing
Zinnia seeds won’t germinate well until the soil reaches 70°F (21°C). That means direct sowing isn’t always reliable if you want to enjoy zinnias in the late spring or early summer. When the soil is warm enough for the seeds to germinate, you must stay on top of water to maintain moisture levels that encourage germination.
Since small zinnia sprouts are more susceptible to pests like slugs, snails, and pillbugs than larger seedlings, directly sown zinnias are more likely to succumb to pest damage.
How to Start Zinnia Seeds Indoors
Starting zinnias indoors allows you to get a jump on the spring growing season. Aim to start your seeds four to six weeks before you plant to transplant them outdoors.
Numerous containers work well for sowing zinnia seeds, but I prefer six-cell trays. They provide enough space for the plants to develop strong root systems, but they don’t take up excess space.
Fill the trays with a well-draining potting mix designed for seed starting. Gently tamp the trays on a table to let the soil settle, then refill any new empty space with potting soil. Make a quarter-inch hole in each cell, place one seed, and cover with soil.
Water the soil and place the trays in an area that’s between 70-80°F (21-27°C). If you don’t have a warm area, you can place your trays on a heat mat to warm the soil and encourage germination. You should see seedlings emerge in three to seven days.
Once the seedlings emerge, place them in an area that receives eight to twelve hours of bright, direct light. If you don’t have a greenhouse or south-facing window, you can use a grow light to provide crucial light. Keep the soil moist as the seedlings grow.
You can transplant the seedlings once they have their first set of true leaves or wait until they grow larger. However, plant them outdoors before their roots become rootbound. Make sure to slowly acclimate the seedlings to their new home before planting them in the ground.
Pros of Sowing Indoors
Starting zinnia seeds indoors allows you to grow healthy seedlings when the outdoor soil is too cold for the heat-loving seeds to germinate. That means you can start harvesting zinnias a few weeks earlier than you would if you directly plant seeds outdoors.
Sowing indoors also allows for better germination rates, as you can easily control the temperature and soil moisture levels. This means you won’t have to deal with gaps in your garden.
Cons of Sowing Indoors
Sowing indoors involves more equipment and work than direct sowing. Therefore, it’s not the best option if you’re short on time or money.
Keep the Soil Moist
Regardless of whether you direct sow or transplant, you’ll soon have zinnia seedlings growing in your garden! While mature zinnia plants can withstand moderate periods of drought, tender seedlings don’t have robust root systems to tolerate dry soil. Therefore, keep the soil moist for the first few weeks after planting.
When you water, aim to keep the stems and leaves dry. That means using a hose or watering can to apply water near the base of the plants or installing a drip irrigation system. Wet leaves are more likely to develop common yet devastating fungal diseases like powdery mildew.
Pinch Seedlings to Encourage Bushy Growth
Once your seedlings have at least three sets of true leaves, it’s time to pinch them. This practice involves removing the top set of true leaves from the plant. You can also remove more than one set of leaves as long as you leave at least two sets of leaves on the stem.
I like to use a pair of snips to remove the top pair of leaves, but you can also pinch the stem with your fingers or cut it with a knife.
While pinching may seem counterintuitive, removing the apical growth point encourages the plant to develop bushier growth. This results in stronger plants and more flowers.
Provide Support
While zinnia plants can grow well without additional support, most plants benefit from trellising or staking. Staking encourages the plant to grow upright and produce long, straight stems that are perfect for creating bouquets.
Flower farmers use horizontal plastic netting to support their flowers, but this method is often overkill for home gardeners. If you only have a few plants, you can support them with a stake and a few pieces of twine or a metal tomato cage. And if you aren’t worried about straight stems, feel free to let the plants grow wild.
Stay on Top of Flowers
Most zinnia plants will begin to flower sometime between two and three months after you sow the seeds. Whether you hope to harvest every flower for bouquets or leave the blooms on the plants to feed pollinators, keep an eye on the flowers.
You can harvest stems when they are rigid and no longer wiggle when you shake them. Harvesting limp stems will lead to flowers that quickly wilt in a vase.
Harvest in the morning or evening when the air is cool, strip off any remaining leaves on the stem, and place the stems directly into a bucket of cool water. Once you’re done harvesting, move the flowers into a cool indoor space. These tips will help your homegrown zinnias last as long as possible.
If you want to leave the flowers on the plant, deadhead blooms once they turn brown. This will encourage the plant to produce new flowers.
