How to Plant, Grow and Care For Petunias
Are you thinking of adding petunias to your garden this season? Blooming in many different colors, these beautiful flowers are a summer staple in the flower garden all over the world. In this article, gardening expert Paige Foley takes you through every aspect of growing petuinas and their care.
A classic garden favor, petunias are sure to paint your garden in numerous colors with long lasting blooms. With hundreds of varieties available to plant, there are endless options to fit any garden space. Petunias can bloom in bright whites, dazzling pinks, vibrant yellows, vivid purples and even a variety that blooms dramatically black. And, there are several varieties that have bi-color blooms.
They have a wide variety of flower sizes and can have double or single bloom patterns. They are a low-maintenance tender perennial in high hardiness zones. In cooler regions, they are colorful annual flowers that die once the first frost hits.
No matter if you’re growing as a perennial or annual, this article is going to cover everything you need to know about petunias and their care. Let’s dig into the details of how to care for these very popular garden favorites.
Petunia Plant Overview
Plant Type Tender perennial
Plant Spacing 12 inches + depending on variety
Native Area South America
Sunlight exposure Full Sun
Plant height 12 to 24 inches
Water requirements High
Plant Depth 1 inch for seedlings
Hardiness Zones 3-11
Soil Type Moist, well-draining
Pest Aphids, Slugs, Snails
Diseases Root & Crown Rot, Powdery Mildew
Petunias are a very popular tender perennial. They come in a variety of colors, sizes and shapes. With a wide range of hardiness zones, they can be grown just about anywhere.
Petunias are sensitive to cooler temperatures and in most climates are treated as annuals. But in warmer hardiness zones, petunias can bloom year-round. They are short-lived perennials and will finish blooming after a few years.
Luckily, they self-seed quickly. This means they will replace older, dying petunias with new ones and keep filling in blank space. Self-seeding can result in different colored blooms from your original variety. They tend to revert to yellow, white, purple or pink.
Types of Petunias
With so many varieties to choose from, where do you even start? Before you start growing petunias, it’s important to understand the types of petunias available. They are divided into 5 different categories and each category has unique characteristics based on flower and plant size.
Grandiflora are known for their big, vibrant blooms. They don’t produce as many flowers as the other types but they make up for it in size. Their big and showy flowers are 3 to 5 inches across. They form a mound and grow up to 24 inches tall and 36 inches wide.
Multiflora have numerous flowers that tend to be smaller about 2 inches wide. They only get to about 12 inches tall and 15 inches wide. They are a great option if you are looking for a compact option.
Milliflora are the smallest of all, in flower and plant size. With a single bloom they only get to about an inch and half in diameter. Milliflora will make up for size in bloom production all season long.
Floribunda is a hybrid of grandiflora and multiflora. They produce large blooms like the grandiflora but have the height and width of the multiflora. They grow to anywhere between 8 to 15 inches tall and 10 to 12 inches wide.
And last but not least are spreading or trailing varieties. These are pretty self explanatory. These cultivars have vigorous growth and spread easily. With the ability to cover up to 10 square feet from one single plant, they will fill any space with beautiful blooms.
Understanding the types of petunias there are will help narrow your search for the right petunia for your space. Once you have decided what type of petunia you want to grow, you just have to choose a color or variety within that group.
When To Plant
Once the risk of frost has passed in the spring, you are safe to start planting outdoors. Keep an eye on the forecast and make sure to use protection if a late frost comes through your area. While they can be grown from seed, they are commonly available at local garden centers as transplants.
You’ll want to look for short and compact petunias. Leggy plants with numerous blooms are further along in their growth and will have a harder time adjusting after being transplanted. If the selection at your nursery is only leggy plants, you can prune them once you plant them. They may be a bit delayed but will recover quickly.
If you choose to grow petunias from seed, you will have to plant ahead. Petunias need to be started indoors 6 to 8 weeks before the last frost. Once your seedlings have 3 to 4 leaves, you can transplant them outdoors.
How to Grow
When it comes to growing petunias, there are many important aspects to their care. You need to make sure they are spaced properly, have adequate light, water, and are planted in the correct type of soil. Let’s take a look at the most important aspects of their growth, and what you should plan for when adding petunias to your flowerbeds this season.
Plant Spacing and Depth
Spacing and depth is going to depend on the variety you choose to plant. Some petunias stay compact and others have a tendency to spread. When planting your petunias, make sure you leave enough space depending on the variety you choose to plant.
Most petunia varieties get to about 12 to 24 inches wide. But there are exceptions. Some are smaller and some are bigger. Trailing or spreading petunias tend to be the largest of all petunias and can get upwards of 5 feet wide. Of course, this is all dependent on variety and environment.
Milliflora varieties are the smallest in flowers and plant size. They only get to about 8 inches wide. If you are unsure how wide your petunias will get, the nursery tag should have that information or ask a worker.
Planting depth is simple. If you grow from seed, plant about an inch into the soil. If you choose to plant potted petunias, dig a hole that’s the same size as the pot itself. This will ensure you get the plant deep enough into the ground to cover the roots.
For the best results with many blooms, plant in full sun. They can tolerate some shade but should have at least 6 hours of sunlight per day. If you live in warmer regions, petunias can handle partial sunlight. Try to have partial shade in the afternoon when the temperatures are at their peak.
Afternoon sunlight can be too intense for most plants and petunias are no exception. It’s to see lower bloom production once the temperatures in mid-summer become too warm. They will still continue to bloom, just slightly less than previously.
No need to spend extensive time on soil preparation for petunias. Petunias aren’t particularly picky when it comes to soil types. As long as your soils are well-draining, petunias learn to adapt. Neutral to slightly acidic soils are preferable.
If your soils have a tendency to be poor draining, consider incorporating organic matter to improve overall health. Adding organic matter to soils that are heavy in clay or sandy is also beneficial.
Like many annuals, petunias need frequent waterings to ensure lasting and continuous blooms all season. They do not tolerate dry soils for long periods of time. This can be difficult in the heat of summer and might require you to water them every day.
Monitor your soils for moisture every day to ensure your petunias don’t become too dry or too wet. Avoid soggy soils as these tendy to lead to leggy plants.
If your region is experiencing hot and dry weather for long periods of time, be sure to water frequently. Morning and evening water is best because temperatures are cooler and the plant has time to absorb the water. The afternoon heat can dry soils quickly, even if you just watered.
Climate and Temperature
Petunias can grow in a wide range of climates and will behave differently in colder climates than warmer climates. In hardiness 10 to 11, petunias are tender perennials and will bloom all year long for many years. Lucky you!
Now colder regions, we aren’t so lucky. Petunias are considered an annual in these regions and will die once the first frost hits. They will bloom beautifully during the summer but unfortunately fizzle out once temperatures become too low.
The ideal temperature for petunias is 60 to 75° F during the day and no lower than 55° F during the night. They can tolerate temperatures a little higher and a little lower than stated but not for long periods of time.
In northern regions, frost can set in pretty early but daytime temperatures are still warm enough for petunias. If you want to protect your petunias from frost, place a sheet over them or bring the pots or hanging baskets indoors. This can extend their life a few more weeks.
Feed at the time of planting with an evenly balanced fertilizer of your choice. I personally use a slow release fertilizer. You can fertilize as needed if your plants or blooms are beginning to slow.
Be sure to do some research on the varieties you are planting because some petunias require more or less fertilizer than others. If you’re looking for an alternative fertilizer, you can incorporate compost into the soil.
Once mid-summer hits, petunias start to become stringy, leaves will yellow, and few flowers remain. When they aren’t looking like they once did, it’s time to prune. Pruning will make a noticeable difference and keep them blooming all summer long.
You can start pruning once you plant them in your yard. Every week, clip a few longer stems in half. This may mean you need to trim some stems that have gorgeous flowers on them. But I promise, it’s worth it! As your plant grows, continue to trim longer stems to avoid leggy petunias.
If you get a variety that isn’t self-cleaning, you will have to deadhead weekly. Simply, remove the shriveled and wilting flowers from the stem and discard. This will allow your petunias to produce more blooms and prevent them from self-seeding.
Propagating petunias is pretty simple and done by stem cutting. Typically, gardeners propagate petunias because they want to save a particular variety. The variety may be hard to find at nurseries and they want to continue growing it year after year.
Prior to any frost in the fall, take about 6 inches of young healthy stems for propagation. Remove the bottom half of the leaves and dip the end in root hormones. Root hormones aren’t necessary but can make it easier for the plant to establish roots.
Plant each stem in a container with loose potting soil and place in indirect sunlight. Keep the roots moist and they should emerge within a few weeks. Store them indoors all winter until spring when the risk of frost has passed.
By propagating in the fall, petunias will be leaps and bounds ahead of others that you purchase from a nursery. Blooms will set quicker and you will have a bigger, healthier plant to transfer outdoors. Not to mention it’s much quicker than growing from seed!
Growing Petunias from Seed
If you are looking for a challenge or just love watching all your hard work come to live, you can plant petunias by seed. It’s definitely less common and more time consuming than buying potted petunias from a nursery.
You will want to start seeding indoors 10 to 12 weeks before your zones anticipated last frost. Begin by gathering your supplies like pots, potting soil and seeds. Fill your pots with potting mix and spread the tiny seeds on the surface of the soil. Press the seeds into the soil but do not cover them.
Covering the seeds won’t allow any light to reach them and they will struggle to germinate. Cover the pots with clear plastic or a plastic bag. You should see seedlings emerge within 10 to 12 days. Once they emerge, remove the clear plastic or plastic bag from the pots.
Keep indoors until their true leaves emerge and the risk of frost has passed. You can then transplant them outdoors to your desired location.
Growing in Pots or Containers
Petunias are one of the easiest plants to grow in a container or hanging basket. They provide continuous color all summer and into the fall. There are a few things to consider when planting in a container of hanging baskets.
You must choose the right container for petunias. Aim for a container that’s at least 12 inches in diameter and has proper drainage holes. If your pot doesn’t have proper drainage, your plants will be susceptible to root rot.
If you choose a trailing variety such as a ‘Wave’ petunia, you will need a tall and wide pot. This variety gets very long and will cascade over any pot or hanging basket. They can overpower other plants in the container and tend to do best alone in containers.
Be sure to place your container or hanging basket in an area with proper lighting. Petunias grown in pots may require more frequent waterings than those planted in the ground. Check daily to determine if you need to water or not.
Growing into the Ground
Petunias will also perform well when planted directly into the soil. Once you identify a sunny, well draining area, work the soil well to loosen it. This is a great time to add in some organic matter to help improve the overall health of your soil.
Follow proper spacing according to the variety to ensure your petunias cover the area you intend too. Water well once you finish planting. Remember to check your soils to gauge if they need more or less water.
How to Keep Petunias Blooming
The best part of petunias are the beautiful blooms. So how do you keep them blooming all season or year long?
First, as discussed – make sure you provide the proper sunlight and water requirements. Pruning is going to make a large difference in the number of blooms your petunias produce. It may be scary to cut back stems or even flowers, but it’s worth it when done.
Deadheading spent blooms is going to help as well. By deadheading, the plant puts less focus in seed production and more into flower production. Keeping them clean is not only going to make them look neater but also maximize bloom yield.
Although petunias are beautiful on their own, they really shine when planted next to other petunia-friendly companion plants. You can plant them with most flowering annuals or perennials. This is where you can be creative and create your own arrangement.
They are a great choice to grow next to vegetables. This is a common practice to help attract pollinators to the vegetables and improve yields. Some say petunias keep insects away from their vegetables. But they are at their best when planted in containers with other plants. The ideas are endless when grown in containers with other plants.
Excellent Companion Plants
- Red Salvia
- Fountain Grass
While there are plenty of fantastic companion plants, I recommend sticking with plants that will get taller than 2 feet. Petunias may cover and overpower shorter plants.
There are endless options of petunias to choose from. With a wide variety of colors, bloom and plant size, there is a variety out there for everyone! Below are some of the more popular varieties you can grow in your flowerbed, hanging basket or container.
- ‘Limelight’: This beautiful hybrid is so unique with a lime green outer edge and a magenta center, they are sure to be the highlight of your garden.
- ‘Wave Blue’: This gorgeous trailing petunia has vibrant blue blooms which look excellent in a cascading hanging basket or container.
- ‘Celebrity’: This variety is a multiflora variety that displays a variety of colors. Some common colors for this petunia are purple, salmon, red, yellow, pink or a variety of all those colors.
- ‘Carmine’: This variety is pretty and petite with miniature flowers that bloom in a true magenta color. A great option in containers as it won’t overpower companion plants.
As with all plants, petunias aren’t immune to a few basic problems. You may run into leggy plants, or wilted flowers and leaves. Many of the issues that plague them have to do with soil quality, sunlight or watering mishaps, and pests or diseases. Let’s take a deeper look.
Wilted Flowers or Leaves
There could be a number of reasons your petunia flowers are wilting but most likely it’s because it’s getting the wrong water requirements. Too much or too little will cause the plants to show signs of wilted leaves and flowers.
Check your soils regularly to ensure proper moisture. If they are dry, consider giving them some extra water and if they are too damp, consider backing off on a watering or two.
This is a common problem with petunias but luckily one of the easiest to fix. Deadhead the flowers regularly and pinch back the leggy stems. This should allow the plant to become fuller. As the plant continues to grow, your plants will become less leggy.
Root, Stem and Crown Rot
These types of disease develop when planted in areas of poor drainage or they are overwatered. The leaves will begin to wilt and continue to wilt even after regular waterings. Correcting the poor draining soils and watering less is the only solution to stop the disease progression. Pull plants that have progressed too far and are unsavable from the disease.
Frequently Asked Questions
Are they deer and rabbit resistant?
Sadly, no. This can be a true challenge because deer and rabbits love to munch on their delicate blooms. They will nibble on the blooms or rip the plant from the ground completely.
Why have my petunias stopped blooming?
Begin by checking the environment you are growing them in. Is there enough sunlight? Are they getting enough water? These are common factors that can affect the production of blooms and should be adjusted accordingly.
Will they clean themselves?
This totally depends on the variety you choose to grow. Newer varieties tend to be self-cleaning where older varieties are not. Do some research before choosing a petunia if you are interested in varieties that are self-cleaning.
Petunias are a classic gardening staple that bloom all season long (or all year long) depending on your hardiness zone. With a wide range of colors and sizes, there is a petunia for every type of gardener out there. They look great in flower beds, vegetable gardens, containers and hanging baskets. No matter what variety you choose, they are sure to make a statement in your garden this season!