Can You Winter Sow Zinnias?
Zinnias are a summer blooming favorite that couldn't be easier to grow. If you're wondering whether you can winter sow these cheerful flowers, follow along as gardening expert Melissa Strauss explores the idea.
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For as long as I have a garden to tend, I will grow zinnias. They’re easy-going, with a carefree nature that makes them adaptable and versatile. They make wonderful cut flowers, and they’re incredibly attractive to pollinators. If you want to bring bees to your vegetable garden, toss a handful of these seeds nearby.
Zinnias are warm-weather plants that are native to Mexico. They are drought and heat-tolerant, and most varieties have a cut-and-come-again habit. In fact, the more you cut, the more they branch, and the more flowers you will have.
These colorful annuals are not particular about how you start them. They take well to directly sowing, and they transplant easily, so starting indoors is also a good option.
While we typically associate these with summer, you may wonder if you can winter sow these to see them flower earlier in spring. Let’s take a look and see if winter sowing will work for your zinnias.
The Short Answer
Technically, yes, you can winter sow zinnias, but it’s not advised. These are warm-weather plants. They need warm soil to germinate, and they don’t require cold stratification. That’s not to say that no one has ever done it. It’s just not typical.
Zinnias germinate quickly and can sprout in a matter of days if the weather is right. A thaw mid-winter can cause them to sprout, and then they will die off as soon as the cold weather returns.
The Long Answer
I’m not going to tell you what you can and can’t try in the garden. Great discoveries often come from experimentation. You may discover a completely new method of growing zinnias that makes winter sowing possible. If you were to try it, this is how it might work.
How it Works
Winter sowing is a great method of seed starting for plants that like cold weather or need some cold exposure to germinate. This method of cold stratification is close to the way it happens in nature. The freezing-thawing and exposure to moisture help break down the hard covering of the seed.
As the outer coating breaks down, the seed becomes more receptive to water. As soon as the soil warms up to the right temperature, the seeds will germinate and start growing quickly.
Winter sowing is different from directly sowing zinnias as you might in the fall. Instead of planting them directly in the ground, you use clear, lidded containers. Milk jugs work well. You place the containers with soil and seeds outdoors and let nature run its course.
Pros
Winter sowing has some great benefits for the plants that work well this way. It saves money on equipment like grow lights and heating mats for indoor planting. All you really need are some empty milk jugs or other comparable containers, and some seed starting mix.
For those living in smaller spaces or for anyone who just doesn’t have much space to spare, starting indoors can be a hassle. This method gets everything outdoors as soon as possible and leaves it there.
Because they are technically growing outdoors, they get a lot of sunlight. This eliminates the need for hardening off your seedlings, which can be high maintenance and time-consuming. Instead, your plants will be strong and sturdy, as they won’t need transplanting, and they will set down substantial roots.
Cons
The general disadvantages of winter sowing are minor, but for zinnias, they make a difference. For one thing, cold fronts can roll through any time, and before your last anticipated frost date, that puts frost-tender seedlings at risk.
Zinnias are not cold-tolerant at all. They are some of the most heat-loving plants in my garden. As soon as that first frost happens in the fall, they’re done for. That means that if they sprout in your containers and then an unexpected cold front moves through, your seedlings will likely die.
The seeds also prefer warm soil temperatures (around 70-75°F) to germinate, so this method requires you to wait longer compared to starting indoors.
The other potential disadvantage is that they won’t be on your radar as much as seeds started indoors. This is a universal issue, as all seeds need some attention and moist soil to keep them healthy and going through the stratification process.
How to Plant Zinnias
We’ve talked about a less effective method to use for these flowering annuals. Now let’s discuss a better method! When the conditions are right, these are incredibly easy to grow. They are drought-tolerant once established, and they are happy in the heat of summer, even here in Florida!
Although they are not picky about soil, loose, well-draining soil will give you the best root development and fastest growth. Very heavy or compacted soil can slow down their roots. They even tolerate poor soil, though I always mix in or top dress with some compost or manure. Mixing these materials into heavy soil can help to loosen things up.
One important factor in growing these annuals is sun exposure. They need a lot of it. If you can find a spot that receives eight to twelve hours of direct sun daily, that will be ideal. Less sun will lead to leggy, spindly plants with fewer flowers.
You can directly sow zinnias in the garden, so there is no need for seed starting trays or other expensive equipment. Sow three seeds every 6″-18″ apart, depending on the size of the variety. They don’t need light to germinate. They should pop up in about four to seven days.
When your seedlings have four leaves, thin them out to one plant in each spot. I’ve found these thinned-out seedlings transplant quite well. I don’t toss them. Instead, I find other spots in the garden to plant them. Some may fail, but most take.
If you want nice, bushy plants with tons of flowers, pinch your seedlings after they get their third set of leaves. Use your fingers to pinch off the top of the plant, just above the second set of leaves. Pinching encourages branching. I like to do another round of pinching when each new branch has two sets of leaves.
Zinnias like deadheading. In my experience, for every flower you cut, two more will result. By mid-summer, you should have a bed full of these sturdy, cheerful flowers. Give them more water in the heat of summer. Mulching will help to hold moisture in the soil.
With proper care, they should continue to flower until the first frost. Nearing the end of the season, if you want them to return, leave some flowers on the plant and let them go to seed. These self-seed well in many environments. After years of growing them, I get plants popping up all over my yard!
