When To Plant Zinnia Seeds And How To Grow Zinnias From Seed

Zinnias are some incredible flowers that bring a late-season burst of color to your garden from midsummer well into fall.

These lovely plants can be divided to create more Zinnia flowers, but there’s just something satisfying about growing a plant from scratch.

Planting Zinnia SeedsPin

This handy little guide will help you grow zinnias from seed and show you how to harvest the seeds if you don’t want to go out and buy packets.

When To Plant Zinnia Seeds

The exact time to plant can vary a lot depending on where you are and how you’re germinating them.

However, the key is that they’re highly cold intolerant and cannot be planted outdoors until all risk of frost has passed.

Harvesting Zinnia Seeds

Let’s start with the option a lot of people never think of – harvesting seeds from your existing zinnias.

Please note that using seeds from most cultivars will likely result in one of the parent plants, and some cultivars are sterile, so you’ll need to divide those specimens unless you don’t mind a surprise.

A few exceptions to this rule are cultivars known as “open-pollinated,” and if you have one of the following examples, you’ll be able to get the same plant out of the seeds:

  • ‘Cactus Bright Jewels’
  • ‘California Giant’
  • ‘Canary Bird’
  • ‘Candy Cane’
  • ‘Cut ‘n’ Come Again’
  • ‘Green Envy’
  • ‘Jazzy Mix’
  • ‘Lilliput’
  • ‘Red Spider’
  • ‘State Fair Mix’

Once you know you have a zinnia that fits these rules (or want that surprise plant), you have another little hurdle to overcome: cross-pollination.

When you see buds forming on zinnia plants, you want to keep them pure and put little baggies over the buds, leaving them loose enough to permit blooming.

This will prevent pollinators from accessing the flowers until you’re ready, meaning you can expose only specific species at a given time so you know you won’t end up with a hybrid.

Once your desired flowers are pollinated, you’ll have to resist the urge to deadhead and allow the heads to dry out.

This allows the seeds to mature properly, and it’s only safe to harvest the flower heads once they turn dark brown and are dry to the touch.

You may wish to discard the heads of any zinnia suffering from powdery mildew, as this fungus can infect the seeds.

Remove the ripe seed heads and place them on screens for about a week to ensure they’re thoroughly dried out on all sides.

Make sure you always keep the seeds and seed heads from different plants separate and labeled so you know which seeds are for which plants.

Finally, place a seed head on a paper towel and gently hit it several times to dislodge the seeds.

You can also try ripping the seed head apart and manually removing the seeds.

Be sure to remove any remaining petals from the seeds and any other debris.

Storing Fresh Zinnia Seeds

Spread your seeds and allow them to air dry for a few more days to reduce the risk of mold or rot setting in while they’re being stored.

Stick them in an envelope or paper lunch bag and mark the plant’s name on the outside and the date.

Zinnia seeds have shelf viability of 3 to 5 years, so having a date will help you prioritize your future plantings.

Store this bag or envelope in a sealed glass jar in a cool, dry spot away from bright light until needed.

Planting Seeds Indoors

Germinating seeds indoors can not only be a lot of fun, but it also gives your plants a head start.

You can use ceramic or terra cotta pots, but a better option is to germinate the seeds in peat pots, as these can be planted directly into the ground later without stressing the plant too much.

Seed trays aren’t a good option for this plant, as the roots are fragile and easily broken when handled.

Aim to plant the seeds approximately 6 weeks before the final frost is due.

Remember the spacing your zinnias will need, which can vary from one species to another, as this will prevent you from growing too many to fit in the garden.

Using a starter potting mix for your soil, gently press each seed 1/4″ inch deep.

Zinnias need a soil temperature of 60° to 70° degrees Fahrenheit to germinate properly, so avoid a spot with a risk of chills or drafts.

Keep the soil lightly and evenly moist and provide bright, indirect sun until the seeds germinate.

You should see them poking out of the ground in about a month.

If the final frost has passed, you can transplant the seedlings to your garden or move pots to a sunnier location.

Planting Seeds Directly Into The Garden

Planting in a garden isn’t much different from starting indoors, although there are some important differences.

First, you’ll need to wait until the danger of frost has completely passed.

The soil should be at least 60° degrees Fahrenheit to ensure proper growth.

You’ll also need to loosen the soil several inches down to make it easier for the delicate roots to grow.

The ideal conditions are a spot with well-drained soil, amended with organic matter, and exposed to full sun.

Once the seeds germinate, you can thin them out so only the strongest remain, but remember that the roots are fragile, so it’s better to remove the weaker ones and leave the strong plants undisturbed when possible.

Transplanting

This step is incredibly simple if you start the zinnias indoors in peat pots.

Just dig holes at proper intervals, slide your peat pots in, and backfill.

It’s a more delicate operation removing them from a sturdier container, however.

Try to slide the plant out, soil and all, and plant this in the hole.

If the soil breaks apart, try not to disturb the roots and plant as gently as possible, so there’s minimal risk of damaging them.

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