5 Secrets for Growing Massive Petunias

Petunias are a popular annual for a reason - they’re colorful, showy, heat-tolerant, and easy to grow. With the right plant selection and a few tricks up your sleeve, you can grow truly massive petunias. Whether you plant them in the ground, in containers, or in hanging baskets, huge petunias are a showstopper. Garden expert Christina Conner shares five tips for growing massive petunias.

A close-up of vibrant potted Petunia flowers in pink and white hues, with an urban road bustling with cars and green plants in the background.

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Petunias are arguably the most popular annual. They dazzle in just about every color and variegation imaginable with long-lasting blooms. There are hundreds of cultivars in classic shades of whites, yellows, pinks, and purples. Some of the more unusual shades and variegations include black flowers, flowers resembling a night sky or peppermints, and double blooms. Have you ever wondered how to grow massive, magazine-worthy petunias?

These colorful flowers are the star of the show in containers, hanging baskets, or in the ground. They come in two forms—massive blooms like those of the superbissima or the bush-like habits like those of the supertunia. My favorite use is in hanging baskets, where they elegantly drape down and resemble big, fluffy, colorful clouds.

You don’t need to be a professional gardener to grow huge, healthy petunias. Despite their popularity and ease of care, petunias, along with most annuals, grow scraggly and scrawny in midsummer. But it doesn’t need to be that way! Here are five secrets to growing big, beautiful petunias.

Choose the Right Variety 

A close-up of a petunia flower showcasing purple inner petals with delicate, curly edges, set against a backdrop of lush green petunia leaves.
Certain petunia hybrids are bred to grow exceptionally large.

Growing big, showy petunias starts with choosing the right variety. Some are great for small containers and spaces, while others demand ample space to grow. For me – my garden motto is “Go big or go home!”  

There are a few petunia hybrids bred to grow huge. Many of these newer varieties have stronger petals, which won’t turn into a mushy mess when wet. One of the most common large types is the Supertunia Vista ®. Unlike regular supertunias, a single plant can reach up to two feet tall and three feet wide. The standard supertunia ‘Giant Pink’ is also a large option, with exceptionally large pink flowers. 

When you’re looking for a large petunia – it depends on whether you want big flowers or a big plant. Trailing varieties, like those in the ‘Wave’ and ‘ColorRush’ series, are vigorous, fast growers, growing up to four feet long in containers. Grandiflora petunias have the largest flower size (about five inches across) and include those in the ‘Dreams,’ ‘Ultra,’ and ‘Storm’ series.

Petunia ‘Superbissima’ from the Czech Republic boasts giant five to seven inch flowers and an average size, though some gardeners mention these flowers are sensitive to overhead water. This plant is harder to find in the U.S. and will likely need to be started from seed.  

Choose A Large Container 

A close-up of vibrant flowers in a large pot, showcasing colorful blossoms intertwined with lush green leaves.
Opt for spacious containers for abundant blooms.

Big petunias need big containers. Supertunia and grandifloras need spacing about 18 inches apart, and a single plant ends up filling an entire 12-inch pot. While it’s always tempting to overplant containers at the beginning of the season, less is more if you want lush, healthy plants. 

Make sure your site is in full sun. While petunias survive in partial sun, the more sun you provide, the more blooms you’ll get. Ideally, they should get at least six hours a day of full sun, but preferably more if possible. 

So if you see any of these big-growing cultivars at the nursery – don’t go overboard. Remember, every tiny plant in a cell will grow to be much, much bigger. 

Keep the Soil Moist

A close-up of potted magenta flowers with delicate green leaves, being watered by a hand holding a green watering can, set against a lush green lawn.
Morning watering prevents rot.

Petunias don’t like wet feet, but they do need to frequent watering. Those in the ground need to be less frequently watering than those in containers and pots. In containers and pots, especially hanging baskets, petunias need nearly daily watering, even twice a day in super hot weather. As always, check the soil moisture first before watering. 

Because the afternoon sun is the most intense for plants and petunias are susceptible to rot, watering in the morning is best for these plants. For these and other annuals, a drip system is helpful for keeping these thirsty plants alive and thriving in the heat of summer. 

Fertilize Often

A close-up of hands in green gloves carefully spreading white granular fertilizer into the lush green leaves of a plant with red flowers, growing in a brown soil-filled pot.
Choose fertilizers rich in phosphorus for vibrant petunia blooms.

These flowers are heavy feeders and benefit from fertilization as much as once a week and immediately after planting. If this is too much however, every other week would do. A slow-release fertilizer works, but I prefer using water-soluble fertilizer for the fastest results. For petunias, simply replace one of your watering days with a fertilizer day. Pro tip: I like to use old jugs to mix my fertilizer; I am an iced coffee fiend and find these containers make great watering cans. 

Use a balanced fertilizer like an 8-8-8 or 10-10-10. Some gardeners mention that they have bigger and greater blooms with a fertilizer higher in phosphorus. Fish or tomato fertilizers like Espoma Organic Liquid Tomato Plant Food have a higher ratio of phosphorus (1-3-1) which is beneficial during their active blooming cycle. 

Trim and Prune

A close-up of vibrant pink flowers surrounded by lush green leaves, with pruning scissors poised to trim a bloom.
Prune regularly to maintain plant health.

As temperatures heat up in midsummer, these colorful flowers start to look leggy, stringy, and overall just… blah. Some gardeners use July 4th as a date to remember to give their plants some midseason care, but it’s never too late. If your petunias don’t look as beautiful as they once did or have a gaping hole in the center of the plant, don’t worry. It may seem counterintuitive, but one of the best ways to persuade your petunia to bush out with more growth is to give it a haircut. 

One way to prune is to go as they grow. When you notice one stem growing longer than the others, cut it back a few inches to the node. This is a good weekly gardening task. But honestly? My annuals tend to get neglected. In the summer, I’m usually so busy babying my veggies and herbs that I forget all about my beautiful window boxes.

So here’s what I do – I give my petunias a few big chops over the summer when they start to appear not-so-hot, fertilize, water, and call it a day. And ya know what? They’re happy and look great! On your “chop day,” remember all of the usual pruning rules – take no more than ⅓ of the plant and cut at the node. This means taking a majority of the beautiful blooms, so time your chop carefully. If you’re having a big event soon and you want lots of curb appeal, it would be best to wait until a few weeks on either end to cut.  Of course, when a plant is dry or experiencing stress, don’t prune.

You’ll also want to deadhead regularly. Many petunia varieties are self-cleaning, which means that they’ll drop their spent blooms on their own, live ‘Wave’ and ‘Supertunias’. But some, like grandiflora, ‘Superbissima’, and trailing varieties need regular deadheading. This practice promotes more blooms because the plant expends less energy on seed production. To determine whether or not your flowers need deadheading, always check the tag and do some research. If your petunias are already planted, notice if their spent blooms are dropping on their own. 

Before pruning, get a vase ready and make a DIY flower arrangement with your cut blooms. 

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