Zinnias provide beauty and color in our gardens from the earliest days of summer to the very end of autumn. But what if you haven’t planted your zinnias yet? Don’t worry, it’s not too late!
Zinnias are a great choice for midsummer sowings because they grow quickly in the summer sun. So if you have a patch of space in your garden go ahead and plant some zinnias.
Zinnias can be planted as late as July in areas with a long growing season. The plants need 75-90 days from seed to bloom, so a July sowing will mature by September. If you live in an area that doesn’t freeze, you can plant zinnias as late as August, though the blooms will be smaller as the days get shorter.
Zinnia seeds are inexpensive, often sold in packets of 25-50 seeds for just a few dollars (or save your own seeds for free). It’s a small investment to experiment with the timing of your planting, and even if you only get a few blooms, they’ll be well worth it!
So if you’re looking to add a little more beauty to your flower garden beds, don’t wait any longer. Go out and plant some zinnia seeds and see what happens.
What month do you plant zinnias?
Zinnias are typically sown in the late spring, starting in April. The big indicator that it’s time to begin planting is when the danger of frost has passed, which will vary by region. May and June are also great months to sow zinnia seeds directly in the garden.
The ideal soil temperature for germinating zinnias seeds is about 70 degrees, so the daytime temperature should also be in that range. In early spring, it can take the soil a while to warm up, but it stays consistently warm by summertime, leading to fast germination times.
Warm soil combined with full summer sun is a recipe for fast zinnia growth, making July and August viable sowing months, even if they’re considered late compared to spring plantings.
Sow zinnias up until 100 days from the first frost
With 100 days left in your growing season, you can still sow zinnia seeds and get blooms before the first cold snap of fall.
Zinnias take 75-90 days to bloom, so in some cases, you might be butting right up against that first frost date. If you’re new to the term frost date, the quick explanation is that it’s the first date you can expect temperatures to drop to 32 degrees Fahrenheit or lower, which is cold enough to kill most summer flowers.
That date is just an estimate, though, so you could get lucky, and the first fall frost doesn’t hit until a week or two (or later) than when it was predicted.
In that case, you’ll get a couple of weeks’ worth of blooms as a nice bonus. For a cheap packet of seeds, it’s worth pushing the envelope with a late sowing, even if the typical planting window has already passed.
One good thing about a late sowing is that the soil will already be warm from a month or more of the summer sun, so the seeds should sprout very quickly.
To plant zinnia seeds directly in the garden, scatter the seeds over bare soil and cover them with 1/4 inch of soil. Keep the soil moist until they germinate, then water every few days until they get established.
Watch the sowing steps here on FreshcutKY, a fabulous flower gardening channel from Tonya in Kentucky:
While you can technically sow zinnia seeds as late as September, you might not get much from your efforts. The plants may sprout and grow quickly, but they won’t have time to produce blooms before the cold weather arrives.
For the full run-down on starting zinnias from seed, check out this article: Should You Start Zinnias Seeds Indoors? Yes, And Here’s Why It’ll help you get a jump on having seedlings ready for a late planting.
Waited too late? Try winter sowing instead
If the last opportunity to sow zinnia seeds has passed, you can winter sow them with a little planning.
Winter sowing means planting the seeds outdoors in winter, allowing them to stratify (a process of cold-moist conditions that breaks seed dormancy) and then germinate in spring once the soil reaches its ideal temperature.
Zinnia seeds don’t necessarily need cold stratification, but the low temperatures will prevent the seeds from germinating too soon.
You’ll need a container (milk jugs work great), some potting soil, and your zinnia seeds.
Cut the jug in half, fill it halfway with potting soil, and then sow the seeds 1/4 inch deep. Water well, put the lid back on, and tape it shut with duct tape. Leave the cap off for air circulation and moisture to get in.
Once you’ve sowed your seeds, simply place the container outside where it will be exposed to winter conditions. Be sure to label the container, so you don’t forget what’s inside, and check on it periodically throughout the winter.
You should have a beautiful crop of zinnia seedlings ready to plant in your garden by spring!
For a thorough walk-through of the process, here’s another video from Tonya of FreshcutKY:
You can also take the quick and dirty route and simply spring zinnia seeds outside in the soil where you want them to grow. You may lose some seeds to birds and squirrels, so sow them thickly.
Like in the milk jogs, you should have a bevy of zinnia seedlings that will grow quickly come spring.
For either method, make sure to wait to put the seeds out until freezing temperatures have arrived or it’s consistently cold enough that the zinnia seeds won’t sprout too early.
You don’t want them to germinate in October, only to have cold winter temperatures arrive the next week and kill all the tiny sprouts.
Can zinnias survive winter?
If you planted zinnias in spring or summer, the plants will die once winter and cold temperatures arrive. Zinnias are heat-loving plants known as tender annuals, so they can’t survive temperatures under 32 degrees Fahrenheit.
Read more about how frost affects zinnias in this article: Will A Frost Knock Out Your Zinnia Flowers?
However, if you winter sow zinnia seeds, the seed will overwinter just fine. They’ll stay dormant during winter and then come back to life in spring when the temperatures warm up again.
So even though you can’t keep your existing zinnia plants alive through winter, you can replant them each year by sowing new seeds in spring and summer.