The new year is here, and it’s already time to start thinking about starting seeds indoors for our spring vegetable gardens. 

Zinnias, those low-maintenance plants with their beautiful blooms that come in so many vibrant colors, are probably high on your list to grow this spring and summer. But should you start your zinnias inside? Let’s get into it! 

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CAN YOU START ZINNIA SEEDS INDOORS?

Starting zinnia seeds indoors can be a great way to get a head start on the growing season and ensure beautiful blooms all summer long. They are relatively easy to grow from seed and can be started indoors or directly sown into the ground after the danger of frost.

It’s worth mentioning that starting your own zinnias is a much cheaper option than buying a bunch of zinnias from the store. You’ll be in charge of quality control from the beginning, which means you can make sure your flowers never become root bound in their little pots before they’re planted out. Following my organic seed starting methods also means your zinnias will never be exposed to synthetic pesticides and fertilizers, which is much better for our friendly neighborhood pollinators.

Here’s your step-by-step guide to starting zinnia flowers indoors.

STEP ONE: DETERMINE THE BEST TIME TO START FLOWER SEEDS

Don’t know when to sow? No problem. Just google the last frost date for your area, and then count back about 4-6 weeks. That’s when you’ll start zinnia seeds indoors. For those of us in Central Texas, we would start our zinnias by seed in early February so that we can transplant seedlings once our last anticipated frost date passes in mid-March. 

Pro tip:

If you’re still trying to decide what types of zinnias to grow, I recommend Bling Bling Zinnias, Persian Carpet Zinnias, Cactus Flower Blend, and Thumbelina Mix (dwarf zinnias ideal for container gardens). 

STEP TWO: GATHER YOUR SEED STARTING SUPPLIES

You’ll need the following supplies to get started:

A Container to Start Your Seeds in

Zinnias don’t like having their roots disturbed when being planted into the garden so you might consider using biodegradable pots made of coco coir or peat, like these little peat pot trays or round peat pots. These small pots can be put directly in the planting hole to minimize transplant shock. You could also use empty toilet paper rolls on a tray in lieu of planting cells. Again, you’ll plant the whole thing, roll and all, so that those little zinnias roots aren’t disturbed. I have also had lots of success planting zinnia seeds in 4 in seed containers with seed starting mix and just being very careful when planting in the garden by not disturbing their roots to reduce shock.

Grow Lights

These wand lights are easy to maneuver up and down as your seedlings grow. Other options include artificial grow lights that can be affixed to a shelf (like lights mounted under a book case).

Organic Seed Starting Mix

Shop my recommended organic seed starting mixes here, or make your own by mixing equal parts coco coir, vermiculite, and perlite, plus some worm castings.

A Heat Mat

A heat mat is really only necessary if your house is on the chillier side in late winter/early spring. Zinnias germinate best when the soil temperature is between 70°F and 80°F.

Extra: You might also want to have some plant tags to label your rows if you’re starting more than one variety of zinnias.

STEP THREE: PREPARE YOUR POTS/TRAYS

In a large bowl, rehydrate your seed starting mix by adding water and folding it in with your hands until it’s moist but not soggy. Fill your seed starting trays or your little biodegradable pots with the pre-moistened soil mix. Press the mix down a little bit inside each cell and smooth out the surface.

STEP FOUR: SOW ZINNIA SEEDS

Zinnia seeds don’t really need to be buried, so you can just place one zinnia seed per cell or pot, right on the soil surface. Don’t forget to label if you’re planting more than one type. 

Once all your seeds are placed, cover them with a light layer of seed starting mix.

STEP FIVE: KEEP SOIL MIX WARM AND MOIST

Place your seed tray in a warm spot. If you have a heat mat, you’ll set your tray on top until you see the first little sprouts appear. (Using the mat after that can lead to leggy seedlings.) No worries if you don’t have a mat. You can set you tray on top of the fridge or dryer or even just a heating pad made for humans with the fabric cover removed. Warm soil tells seeds for warm-season annuals it’s time to grow. 

Keep the soil moist until the seeds sprout by adding water to the bottom of the tray or spritzing the top of the soil with water from a spray bottle. You can lock in moisture by covering your tray with a plastic dome if you have one. Otherwise, just use a piece of burlap or a kitchen towel. You’ll remove this cover as soon as you see little green shoots appear. Zinnias usually take about 5 to 7 days to germinate.

STEP SIX: TURN ON GROW LIGHTS

As soon as your seeds have sprouted, it’s time to put them under lights. (Again, you’ll also remove the heat mat and any covering.) Keep the lights about 2 inches above the seedlings. If you happen to have a warm outdoor greenhouse, your zinnia seedlings could hang out in there instead of under artificial lights.

STEP SEVEN: TEND YOUR GROWING SEEDLINGS

Once your zinnia seedlings have grown their first set of true leaves, you can use diluted seaweed extract to give them some nutrition every 2 weeks. Aim a small fan turned on the lowest setting at your seedlings or run your hands back and forth over them a couple times a day to simulate wind. This encourages them to form strong roots and prepares them for the great outdoors.  

STEP EIGHT: HARDEN YOUR SEEDLINGS OFF

Before you move your zinnias to their new home in your garden, you have to get them used to outdoor conditions. This is called “hardening off” your seedlings. Basically, you’ll bring them outside for a few hours each day to adapt them to outside temperatures, sunlight, and wind. Doing so reduces shock. 

Wait until all threat of frost has passed before you begin hardening your seedlings off. Ideally, the temps will be above 60°F. Start by placing your seedlings in partial shade for the first couple of days and then gradually moving them to full sun. As you increase sun, you can also increase time spent outdoors. Begin with just an hour outside on day 1 and work up to full outdoor time over the next 7 days.

STEP NINE: PLANT YOUR ZINNIAS IN THE GARDEN

It’s finally time to transplant your zinnias. Hopefully you have a bunch of healthy plants ready to move out to the garden space thanks to all your hard work over the past 6 or so weeks.

You can plant your zinnias in the ground, in containers that have good drainage, or in raised beds. Make sure you plant them in a spot that receives full sun to maximize new blooms. Taller varieties will need to go near the back of the garden space so that they don’t block sunlight from other plants. 

I like to add a layer of compost to the planting area. Dig planting holes that are as deep as your seed trays and twice as wide. Ideally, you’ll be able to plant the entire pots or toilet paper tubes at this time. If not, slide your zinnias out of the tray as gently as possible and try to minimize disturbances to the roots. Space your zinnia plants about 6 inches apart. 

Water your zinnias in well. 

ZINNIA PLANT CARE TIPS

Zinnias really are the easiest flowers to grow. But here are some tips to ensure you have lots of beautiful flowers in a couple of weeks:

  • Aim water at the base of the plants, not the leaves, to prevent powdery mildew issues. You’ll find that you really don’t need to water zinnias very often at all.
  • Treat pests or powdery mildew with Arber Bio Fungicide or Neem oil.
  • Zinnias shouldn’t really need to be fertilized beyond the organic matter (compost) added at the time of planting. If you want to add more nutrients, I like MicroLife Maximum Blooms, a slow-release liquid fertilizer.
  • Pinching off the very first bloom before it opens will encourage your plants to grow bushier and produce even more flowers. Simply cut the stem right above a leaf node (a pair of leaves).
  • Remove spent flowers.
  • Harvest flowers often to encourage your plants to keep producing. Zinnias make beautiful (but not super-long-lived) cut flowers.

Read more about caring for zinnias. Zinnias are annual flowers, so you’ll have to start again next year. Here are step-by-step directions for how to save your own zinnia seeds at the end of your growing season. You’ll end up with hundreds of seeds to start indoors or sprinkle into your garden next year!

That’s all there is to starting your zinnias indoors to get a jump start on your growing season. Shop our Amazon Store to find recommended items you can use for your seed starting endeavors. Let us know if you have any questions!