One of my first gardening memories is of deadheading my mom’s petunias. I found satisfaction in pulling away the sticky spent blooms. As an adult I didn’t want to have to deadhead my annuals throughout the summer. But the variety of colors and petal patterns lured me back to including petunias in my annual containers—and sometimes growing them myself. So, how hard is it to grow petunias from seed? The short answer is not hard at all. In this article, I’m going to share some petunia seed-starting tips, as well as how to plant those young seedlings outside in the spring.

The advances in petunia breeding have resulted in a vast array of color choices, but many are now self-cleaning, meaning deadheading is not required. I think my 11-year-old self would be disappointed! Petunias are native to South America and the first hybrids appeared in the Burpee and Vaughan’s Seed Company catalogs from 1888 to the 1930s.

Why grow petunias from seed?

The main reason to start petunias from seed is for the aforementioned variety. You are not at the whim of a garden center buyer. The choice is yours. Second to interesting colors would be the price. It costs less to grow a flat of petunias than it does to purchase multiple seedlings.

Petunias are drought and heat tolerant, and generally have a long bloom time. I’ve had petunias hold on well into the fall! You just need to do a little gentle prune here and there to keep them from getting too leggy.

Types of petunias

There are many different types of petunias, categorized based on flower size. Here are some of the petunias you may find. The seed packet (or plant tag if you’re purchasing seedlings) should indicate which type of petunia you’re growing. Here are some of the names you’ll see:

• Upright Multiflora: The most durable type of petunia with an abundance of medium-sized flowers
• Hedge multiflora: Great for landscapes with two-inch flowers that bounce back quickly after a heavy rain
• Spreading or trailing multiflora: A low-growing type with medium-sized blooms
• Milliflora: Early to bloom, with smaller one and a half to two-inch flowers.
• Grandiflora: Best for pots or hanging baskets, blooms can be single or double-flowered. These are a little more delicate than other varieties.
• Floribunda: Medium-sized blooms that can be singles or doubles.

Sowing petunia seeds

How hard is it to grow petunias from seed? On the flower scale of difficulty, it’s pretty easy. To sow petunia seeds, you will need soilless potting mix and a seedling tray. Moisten the potting mix with a bit of water before filling your tray. Generally you start petunia seeds in early spring, about six to 10 weeks before the last frost date in your region. Place the seeds on top of the soil and gently press them into the mix.

For germination, petunias like a warm location. Place the seeds in a bright window or under grow lights. Place grow lights about three to six inches (seven to 15 centimeters) above the tray. This can be moved up as the plants start to grow. A seedling heat mat can provide warmth, if necessary.

You want to keep the growing medium moist, but not soggy. Try to avoid letting the potting mix dry out completely. I use a mister to dampen the soil until the seedlings start to grow. It helps prevent the seeds from moving around the tray.

Some seedling trays come with plastic domes that you can place over top to create the environment necessary for the seeds to germinate. Once the leaves form, you can remove the humidity dome.

Transplanting petunia seedlings to bigger pots

When the petunia seedlings have about three to five sets of true leaves, you can transplant them to bigger pots. Gently separate the seedlings from each other using a chopstick or a Little Dibby-type of tool.

Preparing petunias to go outside

Petunias can be planted outside in the landscape after all threats of frost have passed. This is around the time when you would plant your heat-loving vegetables, like tomatoes, or other flowers, like cosmos and zinnias.

Before you plant your petunias, you’ll need to harden them off. That means bringing them outside for a few hours at a time, first by placing them in the shade and bringing them in at night. Then, by slowly introducing them to direct sunlight.

Where to plant your petunias

My petunias usually end up in pots and hanging baskets. I find some varieties make great spillers, cascading over the sides of a container. Add them to window boxes or an interesting urn. Others types of petunias are shorter in stature, so they work well in garden beds. Plants with more compact growth habits also work well as fillers in a container.

Wherever you plant petunias, make sure the area gets plenty of sun. These plants thrive in the heat. You want the soil to drain well. Amend the soil well with compost before digging in your seedlings.

Summer petunia care

Some petunia varieties are self-cleaning, meaning you don’t have to deadhead them throughout the growing season. Others you will need to gently pinch off the flowers.

Petunias can still get a bit leggy and bedraggled looking, especially if there is a long period without rain. Don’t be afraid to cut them back. They will bounce back and rebloom.

Find more articles about growing flowers from seed

• The easiest flowers to grow from seed
• Cosmos
• Calendula
• Pansies
• Marigolds
• Nasturtiums
• Zinnias
• Sweet alyssum