Have you dreamed of growing a cut garden full of beautiful zinnia flowers? I’ll share my tips on growing zinnias from seed indoors, how to transplant seedlings into the garden, and caring for them throughout the season.
Zinnias are beautiful cut flowers that are perfect for beginner gardeners. They’re extremely easy to grow and maintain and are one of the most reliable annual flowers in the summer garden.
Zinnia plants are also one of the easiest flowers to grow indoors from seed.
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Note: I am not a Master Gardener, but a self-taught hobby gardener who shares my opinions and what has worked for me in the garden.
Table of Contents
- Why are Zinnias the Perfect Cutting Flower to Grow?
- When to Grow Zinnias Indoors from Seed
- Supplies You’ll Need to Sow Zinnia Seeds
- Steps for Sowing Zinnia Seeds Indoors
- Step 1 – Choose a Clean Plant Container With Drainage Holes
- Step 2 – Fill Containers with Moistened Seed Starter Mix
- Step 3 – Label or Tag the Containers
- Step 4 – Sow the Zinnia Seeds
- Step 5 – Bottom Water Your Seed Containers
- Step 6 –Place Seed Container on a Heat Mat and Cover
- Step 7 – Pick the Indoor Right Location
- Step 8 – Continue Watering
- Growing Zinnias After the Seeds Have Germinated
- Prepare the Garden Beds for Zinnia Seedlings
- Transplant Zinnia Seedlings to the Garden
- Care Plan for Your Zinnias
- The Most Common Mistakes Made When Growing Zinnias
- FAQ About Zinnias
Why are Zinnias the Perfect Cutting Flower to Grow?
Zinnias are the perfect cut flower for any summer or early fall bouquet.
- Several zinnia varieties with bright and beautiful colors and mixes are available when you grow your zinnias from seed.
- Their daisy-like flowerheads on a single straight stem make them a welcome addition to any summer floral arrangement.
- Zinnias are a low-maintenance plant that attracts pollinators to your garden.
- The more you cut, the more beautiful flowers the plant will produce.
- Zinnias will continue to produce new blooms until the first fall frost.
When to Grow Zinnias Indoors from Seed
When starting indoors, sow zinnia seeds 4-6 weeks before the season’s last frost. You can find your average last frost date HERE.
If you plant zinnia seeds earlier than the recommended time frame, the seedlings will quickly outgrow their pots before the weather has warmed enough to put them out into the garden.
Zinnias can also be sown directly in the ground as soon as the threat of freezing has passed.
Supplies You’ll Need to Sow Zinnia Seeds
Steps for Sowing Zinnia Seeds Indoors
Step 1 – Choose a Clean Plant Container With Drainage Holes
Seed-starting containers should be clean and have drainage holes. You can read my blog post, Supplies Needed for Seed Starting, for several container options. I use cell trays and plastic pots for my seed containers.
If you’re reusing old plastic containers or trays, wash them thoroughly with a 1-part bleach/ 9-part water solution to help kill any lingering diseases or pathogens.
Step 2 – Fill Containers with Moistened Seed Starter Mix
Before adding seed starting mix or potting soil to the container or seed trays, moisten until thoroughly damp but not soaking wet.
Fill the cell trays or container to the top with the moistened seed starter mix. As you go, tap firmly against the table or shelf to ensure the soil settles and prevent air pockets in the containers.
BENEFITS TO USING A SEED STARTING MIX
I recommend using a quality organic seed starter potting mix rather than a regular potting soil when sowing your zinnias seeds for the following reasons:
- lightweight and has a finer texture and higher porosity than regular potting soil, allowing for better oxygen access for seed germination.
- contains fewer nutrients, which is beneficial because it prevents seedlings from becoming leggy and weak
- less likely to contain weed seeds and disease organisms, which can be problematic with a regular potting mix
- usually formulated to maintain a more consistent moisture content, which is vital for successful seed germination
You can make the seed starting mix go even further by filling the bottom half of the container with regular potting soil and then filling the rest with the seed starting mix, where the seeds will be placed.
Step 3 – Label or Tag the Containers
Label the container with the name of the variety of plants and the date planted.
You would be surprised by how easy it is to forget what you’ve planted in a particular container after only a few days.
Step 4 – Sow the Zinnia Seeds
Sow two seeds per container or cell by creating a 1-half-inch hole into the soil in 2 opposite corners. You can use a pencil, dibbler, or even your finger to make a hole.
Step 5 – Bottom Water Your Seed Containers
After sowing the flower seeds, set the container in a drainage tray with an inch of water in the bottom if needed. It’s important not to let the container sit in the water for more than an hour.
It’s important not to overhead water after you’ve placed the seeds in the container. You may wash the seeds away and have to start the process over again.
Watering from the bottom allows the roots to be watered thoroughly.
Step 6 –Place Seed Container on a Heat Mat and Cover
Place the container on a heated mat or in a warm corner of your house, and cover it with a clear plastic dome. This will help speed up the seed-starting germination process.
Step 7 – Pick the Indoor Right Location
Keep your seed starts in a light and bright space, such as a greenhouse or sunroom. If you don’t have that option, keep the seedlings under a grow light.
Step 8 – Continue Watering
Check your containers every other day or so and bottom water when the soil looks and feels dry. Remove the tray of water once the soil surface is evenly moist.
Growing Zinnias After the Seeds Have Germinated
Step 1 – Remove Heat Mat and Uncover the Container
Check the seed container daily. Once the seeds have germinated and the sprouts are visible, remove the clear dome lid and the seedlings from the heated mat.
Step 2 – Continue to Water When Needed
Check the seedlings daily to ensure the soil doesn’t dry out.
The very first leaves that appear on the young plants are called cotyledons. Be sure to bottom water your seedlings until you see the first real leaves that appear after the cotyledons.
Once those second sets of leaves appear, water with a gentle spray from a watering can or hose when needed, usually every 1-2 days.
Step 3 – Transplant the Zinnia Seedlings if Needed
If your seedlings start to outgrow their containers before they’re ready to be planted outdoors, you’ll need to transplant them into a larger container while still growing inside. It’s important to give the roots more room to grow.
Step 4 – Harden Off the Zinnia Seedlings
After all danger of frost has passed, you can begin “hardening off” your zinnia plants before transplanting them into the garden flower beds.
Don’t skip this process! Your plants will go into shock by the sudden change in temperature.
Set the containers in a sheltered spot outdoors, increasing the time they spend outside each day over a week or two. I usually start with 2-3 hours on the first day.
Prepare the Garden Beds for Zinnia Seedlings
Zinnias love heat and full sun, so plan for a location to meet their needs.
This annual plant can be adaptable to most soil conditions. But zinnias will thrive when planted in well-drained soil and organic matter is added.
After acclimating to the outdoor temperatures, transplant the zinnia seed starts into the garden once the threat of frost has passed.
It’s recommended to succession sow zinnias every 2-3 weeks to have non-stop blooming into fall. I personally have never had to do that. I’ve always had colorful flowers until the first frost.
Check the back of your seed packet for spacing directions. Zinnia plants get very bushy and need extra room to spread out, so space plants at least 9-12 inches apart.
Give zinnias lots of space. Good air circulation will help prevent pests and fungal diseases like powdery mildew.
Transplant Zinnia Seedlings to the Garden
Care Plan for Your Zinnias
Support Plants Early
Once planted in the ground, zinnias grow quickly, so be sure to stake them early while they are still young.
I use both the corral method and netting to support my zinnias.
As the plant’s long stems grow taller, add another layer of twine or raise the netting to keep the wind and hard rains from damaging the zinnias.
Water Your Zinnias Regularly
Create a plan to make sure your zinnias will be watered regularly in the garden.
For convenience and efficiency, I set up soaker hoses and drip irrigation in the raised garden beds. These watering systems ensure that my zinnias will never dry, even when I’m on vacation.
Pinch Zinnia Plants
To get the longest stems possible, you should pinch them when they’re young seedlings.
Once the zinnia plants are 12 inches tall and have at least three sets of leaves on each stalk, snip 3-4 inches off the top, just above the leaf joint, with clean, sharp pruners.
Pinching the seedling signals the plant to send up multiple stems and side shoots from below where the cut was made.
Here are some of the benefits of pinching…
- Encourages the plant to branch from the base
- Promotes higher flower production
- Produces longer stems
Harvest Your Zinnias for More Blooms
Zinnias should be cut when fully seasoned or mature. Hold the stem about 8 inches below the flower head and shake it gently.
If the stem bends or is droopy, it’s not ready to be harvested. But strong stems are a sign that the flower is ready to be harvested.
Zinnias are considered a “dirty flower,” which means the water in the vase will discolor faster than other flowers. Add a drop or two of bleach to the water to help it stay clean.
The freshly harvested zinnia flowers should last 7-10 days in a vase if flower preservatives are added. They are very cold-sensitive, so it’s important not to put them in a cooler.
Deadhead Spent Flower Heads
If there are spent flower heads, even after harvesting your zinnias, be sure to deadhead them to help focus the plant’s energy on producing new flowers without going to seed.
Deadheading is the process of trimming the old flowers, which encourages new plant growth.
The Most Common Mistakes Made When Growing Zinnias
Do you want to grow the most beautiful zinnias? Avoid these common mistakes, and you’ll be a pro in no time.
- Not adding support like netting, staking, or corraling at the time you plant your seedlings outdoors.
- Planting too close together, creating powdery mildew and crowding. This also reduces the plant’s flower production.
- Not pinching the plants after they’ve reached 12 inches in height.
FAQ About Zinnias
Q: Do zinnias come back every year?
A: Zinnias are annual plants, so they don’t return every year. Annual flowers complete their life cycle in one year.
Save the seeds of your zinnia flower heads and sow them the following year.
Q: How long do zinnias bloom?
A: Zinnias usually start blooming in early spring and die off after the year’s first frost.
Q: How tall do zinnias grow?
A: Most zinnias grown for cut flowers are taller varieties and grow between 1-4 feet. The tallest zinnias are in the Benary’s Giant Series and grow as high as 4 feet.
The zinnia plants you find at a nursery or garden center tend to be shorter varieties to plant in window boxes and flower containers.
Q: Do zinnias need full sun?
A: Yes, they need 6-8 hours of full sun.
Q: When do you plant zinnias?
A: Plant zinnia seedlings in late spring after the danger of frost has passed.
Q: How hard is it to grow zinnias?
A: Zinnias are one of the easiest flowers to grow from seed and are low maintenance. The seeds germinate quickly.
Q: Do zinnias have pest and disease issues?
A: If you space your plants in the garden beds as directed, it will minimize the risk of spreading disease. Use horticultural oils or insecticidal soap to treat any disease or pest problems.
If you plan on growing a cut flower garden, zinnias will be one of your favorite flowers.
They are easy to grow and have the most colorful varieties to choose from, especially if you’re growing zinnias from seed.
I hope these tips on growing zinnias from seed indoors have helped. I’d love to hear from you in the comments below.
Until next time,
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