Want to grow zinnias in your cut flower garden this year? Learn the best way to start zinnia seeds with this foolproof guide!

Zinnias are the rockstars of the ​cut flower garden​, with their vibrant colors, long vase life, and easy-going nature. Whether you’re a seasoned green thumb or a budding beginner, these cheerful blooms are the perfect choice to add pizzazz to your garden and your home.

But where does the magic begin? With starting those tiny zinnias from seeds, of course!

I’ve been growing zinnias from seed to flower for several years and have learned a thing or two about the best way to do it. Today, I’m sharing my tips and tricks for thriving ​zinnia flowers​ that you’ll enjoy all season long both indoors and out.

Learn how to start your zinnias from seed with these simple tips!

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Deciding Whether to Sow Zinnia Seeds Indoors vs. Outdoors

The biggest question you’ll need to solve for yourself is HOW you want to start your zinnia seeds because there are two ways to get your zinnia journey rolling: starting seeds indoors or sowing them directly outdoors.

Deciding whether to sow zinnia seeds indoors or directly outside depends on a few things. So consider these factors carefully.

Climate

  • Cooler climates: Starting zinnia seeds indoors allows you to get a head start on the season and enjoy earlier blooms before the last frost. This is especially beneficial in areas with short growing seasons.
  • Warmer climates: Direct sowing zinnia seeds is perfectly feasible as long as the threat of frost has passed. It’s simpler and requires less equipment, making it ideal for warmer regions.

Personal Preferences

  • Convenience: Direct sowing zinnia seeds outdoors is generally quicker and less work compared to starting seeds indoors, which requires containers, grow lights (potentially), and more attention to watering and temperature.
  • Control: Starting zinnia seeds indoors gives you more control over germination conditions and seedling care, potentially leading to stronger plants. It also allows you to choose specific varieties that might not be readily available as seedlings.
vibrant zinnia flowers with queen lime zinnia with blush
Queen Lime with Blush Zinnia and other Zinnia Flowers

Other Factors to Consider

  • Planting time: If you want blooms earlier in the season, starting indoors is necessary. For later summer blooms, direct sowing might suffice.
  • Cost: If you are on a budget, starting seeds outdoors may be more cost-effective than purchasing expensive grow lights and other equipment needed to be successful.
  • Variety: Some zinnia varieties might germinate better indoors, especially those with smaller seeds. Check the specific needs of your chosen variety.
  • Experience: New gardeners might find starting indoors easier with more control, while experienced gardeners might be comfortable with direct sowing.

Ultimately, the best way to decide is to consider your climate, personal preferences, and specific goals for your zinnia garden. Experimenting with both methods can help you discover what works best for you and your local conditions.

Here’s a quick summary table to help you better visualize the decision.

FACTORSTARTING INDOORSDIRECT SOWING OUTSIDE
ClimateWarmer climates, short growing seasonsWarmer climates, longer growing seasons
CostMore expensive, need suppliesLess expensive, don’t need as many supplies
ConvenienceLess convenient, requires more attentionMore convenient, less work
ControlMore control over germination and seedling careLess control over germination conditions
Planting TimeEarlier bloomsLater blooms
VarietyMay be necessary for some varietiesWorks well for most varieties
ExperienceMay be easier for beginnersWorks well for experienced gardeners
Things to Consider When Deciding Whether to Start Zinnia Seeds Indoors or Outdoors

How I Start My Zinnia Seeds

Every year, I prefer to start my zinnia seeds indoors because I have greater control and they bloom much quicker. I am a bit of an impatient gardener and want my plants blooming sooner than later, so I prefer to start zinnias indoors about 4-6 weeks before my last frost date under grow lights in my sunroom.

Years ago, when we lived in our former home, I used to have a seed starting station in my basement that worked really well too. I’ve succesfully grown thousands (yes thousands!) of zinnia flowers this way and have found great success doing them indoors.

That said, I’ve got lots of friends that start theirs outdoors with success too. It really is a matter of preference so think through what works best for you!

zinnia senorita and creamy yellow dahlia zinnia
Zinnia ‘Senorita’ with pink flowers

Starting Zinnia Seeds Indoors

If you are like me and want to start zinnia seeds indoors, it is pretty easy to do because they grow from seed so well!

Seeding zinnias indoors is a cost-effective and rewarding way to grow these beautiful flowers, as well as get a head start on the season, particularly if you live in a cooler climate. You’ll have greater access to the many varieties of zinnias available, so they are worth growing from seed if you are up to it.

If you are not sure when to plant zinnia seeds, you’ll need to know your last frost date and count about 4-6 weeks before. But check your seed packet for specific sowing date instructions.

Must-Have Seed Starting Supplies I Use

Pretty pink flowers: Zinnia Uproar Rose with coneflowers and achillea
Zinnia ‘Uproar Rose’ with pink flowers

Directions for Seeding Zinnias Indoors

Sowing zinnia seeds indoors is pretty easy to do and a fun way to wrap up winter. This year, my last frost date is April 24 which means I’ll be sowing my zinnia seeds the week of March 27 at the latest. If you aren’t sure when your last frost date is this year, you can check it here.

How to Start Zinnia Seeds Indoors

  • Zinnias can be started indoors about 4-6 weeks before the last frost date in your locality. Use a seed starting tray or small pots with drainage holes filled with a quality organic seed starter mix that is pre-moistened. I start mine under grow lights and have found great success starting them in both my basement and sunroom.
  • Make a small hole then sow the seeds then lightly cover them with vermiculite. Sow only one variety per cell tray as the different plants will germinate at different times.
  • Cover seed trays with a clear dome and move them under the grow lights on a heat mat to speed up germination. They typically germinate within a few days to a week.
  • Remove the cover when the seeds start to germinate. It’s OK if they didn’t all germinate, more will grow after the cover is removed.
  • Keep soil moist by bottom watering only.

How to Move Zinnia Seedlings Outdoors and Plant Them the Right Way

  • Before transplanting zinnia seedlings outdoors, harden them off by gradually exposing them to outdoor conditions over a period of 14 days.
  • When seedlings are hardened off and ready to plant in the garden, space zinnia transplants in your flower garden about 9 inches apart after the last frost date. Spacing is really important so there’s enough airflow between plants to prevent problems like powdery mildew.
  • Water young plants regularly, keeping the soil moist but not waterlogged. Feed with an organic fish fertilizer for a few weeks and then use a slow-release fertilizer so feeding them is set-and-forget. This will help promote healthy growth and lots of blooms.
queen lime zinnia bouquet in the garden
Hand bouquet of Queen Lime with Blush zinnia flowers

Direct Sowing Zinnia Seeds

Direct sowing zinnia seeds outdoors is a simple and rewarding way to enjoy these vibrant blooms in your garden. But you’ll need to wait until after your last frost date to do it.

Preparation

  • Timing: Wait until all danger of frost has passed, typically 2-3 weeks after the last frost date to be safe. Aim for a soil temperature of above 60 degrees for optimal germination. If you aren’t sure how warm your soil is, you can use a soil thermometer like this one.
  • Choose a sunny spot: Zinnias thrive in full sun, receiving at least 6-8 hours of direct sunlight daily.
  • Ensure well-drained soil: Poor drainage can lead to root rot. Amend your soil with compost, leaf mold, or other organic matter to improve drainage if needed.
  • Clear the planting area: Remove any weeds, debris, or previous plant material.
  • Loosen the soil: Rake or till the soil to a depth of 6-8 inches to create a good planting bed.
  • Mix in compost or organic matter: Amend the soil with 2-3 inches of compost or aged manure to improve fertility and drainage.
  • Rake the soil smooth: Create a level surface for planting.

Sowing Zinnia Seeds

  • Follow spacing instructions: Refer to the seed packet for the recommended spacing between seeds and rows. Common spacing ranges from 6-12 inches for dwarf varieties to 12-18 inches for taller varieties.
  • Sow seeds thinly: Avoid overcrowding, which can lead to competition for resources and disease problems.
  • Plant at the right depth: Gently press seeds into the soil to the depth specified on the seed packet.
  • Cover lightly: Sprinkle a thin layer of soil over the seeds.
  • Water thoroughly: Water gently to settle the soil and ensure good moisture contact with the seeds.
fresh cut zinnia flowers with gomphrena
Fresh cut zinnia flowers

Caring for Zinnia Seeds After Planting

  • Keep the soil moist: Water regularly, especially during hot and dry periods. Aim to keep the soil evenly moist but not soggy.
  • Thin seedlings (if needed): Once seedlings have their first true leaves, thin them to the recommended spacing if they are too close together.
  • Pinching back: Pinch back plants after the first 4-5 sets of leaves to encourage branching with more flowers.
  • Deadhead spent flowers: Regularly remove spent blooms to encourage more flowering throughout the season.
  • Enjoy your zinnias! With proper care, your zinnias should flower in about 6-8 weeks from sowing.

Pro Tips

  • Label your plantings: Keep track of the different varieties you sowed by using plant markers for every single seedling so you don’t forget.
  • Protect seedlings from pests: Consider using insect netting or row covers to deter pests like birds and insects while seedlings are young.
  • Mulch around your plants: A layer of mulch can help retain moisture, suppress weeds, and regulate soil temperature. But hold off adding it until the seedlings sprout and have some growth to them.
  • Consider succession planting: Sow seeds every 2-3 weeks throughout the season to extend your blooming period and have fresh flowers continuously.
zinnias in the cut flower garden by green garden fence

Reaping the Rewards of Your Zinnias

With proper care, your zinnias should start blooming in 6-8 weeks from sowing. Remember to:

  • Deadhead spent flowers regularly to encourage more blooms.
  • Water deeply and regularly, especially during hot weather. I like to set my flower gardens up with drip irrigation set on a timer to make this an easier task for me.
  • Fertilize with a balanced fertilizer. I like to use a slow-release fertilizer so it’s set-and-forget.

I hope this blog post helps you get started on your zinnia flower adventure! If you have any questions or specific tips you’d like to add, feel free to share them in the comments below. Happy gardening!

close up of monarch on a zinnia flower in the garden

More About Starting Zinnia Seeds

Have you ever grown zinnia flowers from seed before? If so, how do you like to start them? I would love to know more in the comments below.

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'Senorita' zinnias at sunset in the cottage garden
Senorita zinnias with pink flowers in the cottage garden

Garden Supplies I Use

Since I’ve been gardening for well over twenty-five years, I’m often asked about the garden supplies and tools that I use most. From pruners to deer repellents, here are some of my favorites that I use in no particular order.

dahlia kogane fubuki in the potager garden

Click here to shop my favorite garden supplies!

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close up of zinnias with pink flowers in cut flower garden
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Enjoy a beautiful day! xo

Stacy Ling

Want to learn more about me?

I’m a master gardener who’s been gardening and growing things for over 25 years and author of the best-selling book, The Bricks ‘n Blooms Guide to a Beautiful and Easy-Care Flower Garden. With a deep passion for gardening, I enjoy helping others find their inner green thumb with all things plants and flowers, as well as finding ways to bring the outdoors inside their homes.

Get the inside scoop about my background as a master gardener, education, and experience, as well as why I started blogging here.

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close up of pink zinnia flower
picture of pink zinnia flower

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