Guide to Growing and Caring for Petunias

beautiful colorful petunias

Petunias are one of the most popular flowers because of their easy-going nature and versatile beauty. They can be found adorning planters, trailing gracefully from hanging baskets, or creating a wave of ground covering color in the garden. Petunias easily brighten a drab green-space, and pair well with other sun-loving plants. They come in a wide range of colors, filling the landscape with continuous, annual blooms. Best of all, caring for petunias is easy. Check out how to care for petunias here.

Grow Petunias from Seed

You can easily grow petunias from seed just like any other flower or vegetable. Depending on your location, start seeds about ten full weeks before the last frost date. While petunia seedlings are generally strong and start well, they do need a long time to mature in time for transplanting. Use a seed starter or potting mix and keep the medium moist. Keep the tray or pots out of direct sunlight until seedlings emerge and cover with a plastic top or wrap to keep moisture in. Once the small plant has two prominent leaves, you can take off the cover and move to indirect light. As seedlings mature around 5 weeks in, supplemental lighting will help them grow strong and reduce the chance of them getting too leggy. You could also place them in front of a window with direct sunlight, or in a warm greenhouse.

When to Plant Petunias

beautiful blue butterflies landing on pink petunias

After approximately ten weeks your petunia seedlings will be strong enough to be transplanted into hanging baskets, pots, or the garden. Make sure the temperature is warm enough and that there is no longer any chance of frost. If you see freezing temps in the forecast, it’s a good idea to keep your seedlings in a pot, tray, or something that can be brought inside for the night when needed. If they are going directly into the garden you may have to cover with frost cloth. Most plants that are started indoors benefit from a transition period into part shade for about one week before being put in full sun. This helps with the shock of the strong outdoor sunlight, much the same as how our eyes need adjusting when we leave a building.

How to Transplant Petunias

If your petunias were started in pods, they can be sown directly into pots or planters. With this medium, root systems are left undisturbed, which can make design and spacing easier to lay out with other plants. It’s not as necessary for in the garden, as sometimes these pods don’t allow the roots to expand enough, and the plant becomes root bound, or the pod starts to lift out of the soil when the temps get hot and the soil dries. Gently fraying or removing this compostable pod layer can help the plant’s roots grow more naturally. If seeds aren’t in pods, gently scoop a few inches below where any suspected roots are, making sure that they are undisturbed as much as possible. If they are in small pots, gently squeeze and tap from the bottom to release them. If seedlings have grown together, choose the strongest looking one and pinch off the other above the soil. Don’t try and detach the two root systems from each other, this often causes too much trauma and you end up losing them both. Better to be ruthless when culling your seedlings.

Petunia Spacing

You may wonder how many petunias you can plant together, but it depends on the variety of petunia. Grandiflora petunias have the largest blooms, with flowers averaging 5 inches. Therefore, you’ll want to space them out more than other varieties, about a foot apart in full sun, or a few inches less in part shade. Multiflora petunias are smaller, but productive, so you’ll need a half foot at least to allow them the space to breathe and create new flowers. Wave petunias are beloved for their upright growth, and ability to fill in a large garden space. If you want to benefit from their spreadability, plant them two to four feet apart. You could plant them closer, but regular pruning would be recommended to keep them from completely growing on top of each other. Essentially, the larger the bloom is, the more space you should plant between them. Always check the tag if you are buying from a garden center, or the seed packet if you are starting them yourself, as they will specify spacing needs.

Light, Water, and Soil Requirements

Petunias do best in full sun with good draining soil and moderate rainfall. Make sure to water when you notice the top two inches of the soil has dried. Generally, they have modest water requirements are usually fine with the regular rainfall in most American climates. Like most other plants, they will need supplemental watering in periods of drought or extreme heat to maintain their beautiful blossoms, and keep them from wilting. Moving them to a shady spot in extreme heat can also help with potential wilting, especially if you aren’t able to water them for a while. They can often protect each other from overheating when planted next to each other in the garden, or with other plants that offer some shade. Remember that patio spaces with a lot of pavement and concrete can increase surrounding temperatures dramatically.

General Care

beautiful purple petunias with white fringe

Petunias are long-lasting bloomers, flowering from late spring all the way to the first frost. While they don’t require a lot of care, some dead-heading can be important, especially for some older varieties. Simply pluck spent flowers that have started to wilt or dry out from their base. Sometimes mature petunias that have grown top heavy, like Grandiflora varieties, will need some extra support, or allowed to trail down, otherwise they’ll bury their heads in the ground. Usually, they just need some time to bounce back with some full sunlight and a dry out period. Planting petunia varieties in proper containers and spacing appropriately will help with any of these problems.

Do Petunias Need Fertilizing?

As mentioned, petunias are prolific growers that don't require a lot of attention, however there are a few things you can do to promote blooms and keep them healthy. Planting petunias in rich soil amended with organic material like composted manure can give them the best growing medium in a garden space. In planters and pots, using potting mix or soil amended with peat moss to allow better drainage and a lighter medium. Garden soil is generally too heavy for pots, and flowers will be dragged down. You can fertilize pots and planters every two weeks with all-purpose organic plant food, or ones made specifically for flowers. Blood meal can help root systems grow strong when flowers are first transplanted: sprinkle a little at the bottom of the planting hole, and a little on top to deter pests like squirrels and rabbits. Always water thoroughly after applying any fertilizer.

Overwintering

Petunias are fairly tough plants, but generally aren't frost-tolerant and will die off once temperatures are consistently below 40 degrees F. If you want to try and overwinter your petunias, you may have some luck by allowing them to go dormant in a covered garage, porch or basement. There are different methods depending on the light conditions you have available in these spaces and how cold they get. They'll only need enough water to keep them from fully drying out when they are in a dormant period. You can also try keeping them in front of a sunny window, but since these plants are fairly cheap to buy in season, there usually isn't a big push to try and save them all winter. If you like the challenge of it, you can also try propagating cuttings which root easily in water.

What to Plant with Petunias

gardener adding petunias to a garden with a pine tree

Petunias can be planted with fruits, vegetables, herbs, trees, bushes, or flowers that have similar light, soil, and water needs. Luckily, many flowering plants have similar needs for full sun, moderate watering, and well-draining soil.

Petunias like to sprawl along garden beds and planter edges, so for aesthetics they work well with taller, upright flowers like zinnias, sunflowers, salvia, marigolds, lantana, daisies, or dahlias. They can also be a nice foreground flower to trees and bushes when planted around the perimeter.

Feel free to combine them with a variety of other contrasting plants, or keep it simple by pairing them with just one other species, like a vibrant green ivy. Best not to plant with calibrachoa as they look like mini-petunias, and would be too similar placed together.

Pansies are similar looking in shape, as well, and tend to be added to spring planters along with other cool-weather flowers like snapdragons and violas, so better to have them in separate pots or areas of the garden.

Petunias love to trail in hanging baskets, especially Supertunia, Surfinia, and Cascadia varieties. “Wave” petunias are best for creating vast mats of flowers in planters and garden spaces. Petunias can add beauty along the edges to vegetable gardens and vining fruit plants, as well.

Petunias are not recommended for xeriscape gardens or with other plants that prefer desert conditions. Therefore, succulents, cacti, aloe, sedums, or stonecrops are not great companion plants for petunias. Likewise, petunias should not be planted with shade-loving or marsh plants.

Add to Vegetable Gardens!

Petunias are wonderful organic pest control as these guardians of the garden don't shy away from the thugs of the insect world. Thriving beds of petunias repel a variety of pests including the asparagus beetle, leafhoppers, and tomato worms.

They've even shown to be effective against some types of aphids and Mexican bean beetles. Tough plants like tomatoes, potatoes, and eggplants can fall victim to aphids, hornworms, cabbage loopers, Japanese beetles, and weevils, but even crops such as beans, basil, corn, peppers, and even grape vines will appreciate the added protection provided by the neighborly plantings of petunias.

Marigolds are also known pest-deterrents, so plant them together for extra flower power!

Plant petunias with basil, tomatoes, peppers, blue fescue, and rosemary for striking patterns. Since petunias come in solid colors like pink, yellow, purple, red, white, and black, as well as bi-color varieties, it’s easy to find something to work with any arrangement.

Petunia Fragrance

Petunias aren’t known for the fragrance as much as they used to be, as breeders have focused more on color over the years. If you want a flower that gives off a potent smell like lilac or lavender, you may want to skip over using petunias in your garden, unless you find a very specific variety called “Evening Scentsation”. To find out if a petunia is fragrant, head to the nursery in the evening, as any aroma will only come out at night because of petunias' circadian rhythms. Tags should also identify whether or not a petunia is known for its fragrance. Another tip off is if any moths are drawn to the flower, as these pollinators seek out the nice-smelling varieties. While petunias don’t offer a lot for beneficial insects like bees and moths, their color does draw them to the garden where you can make sure other pollinator-friendly plants are nearby.

Budget Friendly

Another wonderful reason to add petunias to your garden is that they are very budget-friendly. Their popularity with shoppers means they will always be a mainstay of the garden center stock, and prices are reasonable, if not cheap compared to other flowers. The most choice will be available at the beginning of summer, and there will likely be some sales a few weeks into the growing season, as nurseries want to unload and make way for the next season of bloomers. You can find great deals in the second or third week of summer for petunias and any other garden standards like geraniums and daisies.

Easy to maintain and a joy to behold, petunias do more than add beauty to your garden. They are hard-working, prolific bloomers that will help deter pests and attract pollinators, as well. With so many varieties and colors to choose from, the mighty petunia can be added almost anywhere for some instant vibrancy all throughout the summer. Growing and caring for petunias is easy; the hardest part is choosing which kind you want.