Seed to Seed Guide: Zinnias

by Hannah Brown

Pretty, prolific, and a magnet to native pollinators like Monarch and Swallowtail butterflies; That’s Zinnias! Popular both in flower boxes, pots, and in-ground gardens, Zinnias come in nearly every color of the rainbow and several combinations therein. Native to Mexico and Central America, these heat-loving annuals thrive in Minnesota’s warm summer weather.

There are hundreds of different cultivars, including some developed right here and at the University of Minnesota. Besides the pop of color they add to the landscape of your home garden, Zinnia’s are popular cut flowers, and their blossoms are edible, if a bit bitter. Decorate a cake with them, freeze them into ice cubes, or simply serve the petals mixed into a light garden salad.

Seed Starting:

When starting your Zinnias from seed, it’s best to start them indoors for four to six weeks before planting them in the ground outdoors. In Minnesota, this means that you should sow seeds into indoor pots or trays in late February or early March.

1. Plant the seeds ¼th of an inch deep into sterile potting soil. To help you estimate what this looks like, the distance between the first and second knuckle on your middle finger is approximately 1 inch. (Check yours against a ruler to ensure accuracy.)

2. After planting, cover the seeds with a thin layer of potting soil and moisten them with a spray bottle filled with water.

3. Cover the seeds with a dark plastic cover (a standard black trash bag will do) and place them somewhere warm and quiet to ensure germination 

4. Moisten with the spray bottle or watering can whenever the top layer of soil dries out. You can check this by inserting a finger into the soil to gauge the dampness.

5. Optionally, you can place them on top of a heating mat set to between 70 to 75 degrees to encourage germination.

6. Under ideal conditions, the zinnias will begin to sprout within 4-8 days of planting. At this point, remove the plastic cover and place the seeds in a warm, bright spot either in a sunny window or positioned under a grow light placed 5 to 6 inches above the soil. (Keep in mind when germinating under a grow lamp that you must move the lamp upwards as the plants grow to prevent burning them. The tops of the plants should never be any closer than 4 inches away from the grow light.)

7. A few days after emerging, the first true leaves will begin to unfurl. Once all true leaves have emerged, thin the seedlings by removing and discarding all but the largest, healthiest plants.

8. About 7-10 days before you plan on planting your Zinnias outdoors, bring them outside during the day to “harden them off.” Place them in a warm, sunny spot outside protected from wind and wild animals for a few hours every day, gradually increasing the amount of time they spend outside over the next few days. Zinnias cannot tolerate low temperatures, so bring them indoors if the daily or overnight forecast is below freezing.

Transplanting:

You can transfer the seedlings into in-ground gardens or containers once the threat of frost has passed, around mid-April. Zinnias need lots of sunlight and well-draining soil, so find a spot in your garden that gets full sun exposure for 8+ hours a day. If you have heavy clay-based soil, mix sand or pearlite into the bed you plan to plant the Zinnias in to encourage draining.  

1. Before planting, thoroughly mix in compost or manure into the base soil to provide vital nutrients and water each seedling thoroughly.

2. Dig a hole deep enough to bury the seedling's root ball completely, spacing each hole 8 to 24 inches apart (depending on variety, check your seed packet) to prevent crowding

3. At this point, you can optionally mix in a little extra plant food into the soil at the bottom of the hole.

4. Gently remove the plant from its container, place it into your prepared hole, fill in the hole with the surrounding soil, pack it down securely, and give it a good soak to water it in

5. If you are growing Zinnias in containers, the larger the pot, the better. Follow the same procedure for in-ground planting, and be aware that you will likely have to feed and water container plants more often than their in-ground counterparts.

Ongoing Care:

To encourage big, bright, prolific flowers, remove the dying flowerheads as they appear with a clean, sharp pair of scissors or gardening shears. This process is called “deadheading” and it works by dissuading the plant from putting energy into seed development and putting more energy into new blossoms.

Zinnias don’t like having their feet wet, as it leaves them prone to root rot and fungal infections. Only water when the top 1-2 inches of soil are completely dry. 

When watering, try to avoid wetting the foliage, as Zinna’s can be susceptible to powdery mildew, a fungus that lives on the leaves of many different plants, making them look like they have been lightly dusted with flour or baby powder. The fungus interferes with the plant's ability to photosynthesize, and in extreme cases, stunts its growth

Seed Saving:

Saving Zinnia seeds is one of the easiest seed-saving projects you will ever have, especially if you are committed to deadheading your plants. No need to worry about separating the seeds from the flowers, just store the whole dried flower, and you’re golden!

1. Snip off Zinnia blossoms off the stems just as they are beginning to wilt

2. Hang the cut flowers upside down in a cool, dry place, and let them dry out for a month

3. Once the flowers are completely dry, you can store the entire dried flowerheads in zip-lock bags, or remove the dried petals and store them in an envelope labeled with the variety and date of storage and store them in an airtight container in a cool, dry place, like a cupboard or basement.

4. To separate the seeds from the dried petals, simply rub them together in your hands. The seed should have an arrowhead-like shape and not crumble like the dried petals. Zinnia seeds can remain viable for 3-5 years.

Check out these sources from the University of Minnesota and The Gardenary for more information:

https://extension.umn.edu/flowers/zinnia and

https://www.gardenary.com/blog/5-easy-steps-to-save-your-own-flower-seeds-and-grow-zillions-of-zinnias

For starting with seeds and saving seeds check out our Youtube channel under growing resources for 2023!

What kinds of Zinnias are you growing? Share with us on our Instagram or Facebook at Como Community Seed Library!