Petunias are a top choice among annuals for their vibrant colors, resilience in the heat, and ease of growth. With the right care and a few expert techniques, you can cultivate petunias that are exceptionally large and impressive. Whether planted in the ground, containers, or hanging baskets, oversized petunias can truly steal the show. Gardening expert Christina Conner shares her five secrets to growing giant petunias.
Petunias are undoubtedly one of the most loved annuals. They come in nearly every imaginable shade, with blooms that last all season. With hundreds of varieties, ranging from classic whites, yellows, pinks, and purples to more exotic options like black flowers, starry night patterns, or peppermint-striped blooms, petunias are incredibly diverse. Have you ever wondered how to grow petunias that are big enough to belong in a magazine?
These bright, bold flowers shine in any garden setting—whether it’s containers, hanging baskets, or flower beds. Petunias generally fall into two categories: those with large blooms like the superbissima or bushier varieties like the supertunia. My favorite use for them is in hanging baskets, where they cascade beautifully, creating large, fluffy, colorful clouds.
You don’t need to be a pro to grow huge, healthy petunias. While it’s common for annuals to look a bit leggy and worn out by midsummer, it doesn’t have to be that way! Follow these five tips to grow stunning, massive petunias.
Select the Right Variety
Growing impressive petunias starts with choosing the best variety. Some types thrive in small spaces, while others need plenty of room to reach their full potential. My gardening philosophy? “Go big or go home!”
Several hybrids are bred specifically for larger growth. These newer varieties often have stronger petals, making them more resilient in wet conditions. One standout option is Supertunia Vista ®, which can grow up to two feet tall and three feet wide. Another favorite is the supertunia ‘Giant Pink,’ known for its strikingly large pink blooms.
When selecting your petunias, decide whether you want large flowers or a large plant. Trailing varieties like those in the ‘Wave’ or ‘ColorRush’ series are vigorous growers, capable of spreading up to four feet in containers. Grandiflora types, such as the ‘Dreams,’ ‘Ultra,’ and ‘Storm’ series, boast some of the largest blooms—up to five inches across.
The petunia ‘Superbissima,’ from the Czech Republic, features enormous five- to seven-inch flowers. However, gardeners often mention it’s sensitive to overhead watering. If you’re in the U.S., you might need to grow this variety from seed.
Opt for Large Containers
To grow large petunias, you’ll need equally large containers. Supertunias and grandifloras require about 18 inches of spacing between plants, with a single plant filling a 12-inch pot. While it can be tempting to overcrowd containers at the beginning of the season, remember that giving each plant ample space will result in fuller, healthier growth.
Make sure your petunias are planted in full sun. While they can survive in partial sun, more sunlight equals more blooms. Ideally, aim for at least six hours of direct sunlight per day, but more is always better.
When selecting plants at the nursery, resist the urge to buy too many. Each tiny seedling will grow much larger than you expect.
Maintain Moist Soil
Petunias prefer moist but well-drained soil. Those planted in the ground won’t need as frequent watering as those in containers or hanging baskets. In hot weather, you may need to water petunias in containers daily, sometimes even twice a day. Always check the soil’s moisture level before watering.
Because petunias are prone to root rot, it’s best to water them in the morning when the sun isn’t too intense. For consistent watering, a drip system can be a lifesaver, especially during the heat of summer.
Fertilize Regularly
Petunias are heavy feeders and thrive when fertilized weekly, or at the very least, biweekly. A slow-release fertilizer is an option, but I prefer using a water-soluble fertilizer for quicker results. Simply substitute one of your regular watering days with a fertilizer application. Pro tip: Repurpose old containers (like iced coffee jugs) to mix and apply your fertilizer.
A balanced fertilizer, such as 8-8-8 or 10-10-10, works well. Some gardeners have found that using a phosphorus-heavy fertilizer can result in even bigger blooms. Fish or tomato fertilizers like Espoma Organic Liquid Tomato Plant Food, which has a higher phosphorus ratio (1-3-1), are particularly beneficial during the blooming season.
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Trimming and Pruning
As midsummer approaches and temperatures rise, your vibrant petunias may begin to appear leggy, straggly, and just a bit lackluster. Many gardeners use July 4th as a reminder for midseason plant care, but there’s no strict deadline—you can always give your petunias some TLC. If they’re looking tired or have a bare spot in the center, don’t worry. While it may seem counterintuitive, one of the best ways to encourage your petunias to fill out and grow more vigorously is by giving them a trim.
A simple way to prune is to do it progressively as the plant grows. If you notice one stem growing longer than the others, cut it back a few inches to the nearest node. This weekly maintenance helps keep your petunias bushy and full. But truth be told, I often neglect my annuals. During the summer months, I’m usually preoccupied with tending to my vegetable and herb gardens, leaving my window boxes and ornamental flowers to fend for themselves.
So here’s my approach—I give my petunias a few big trims throughout the summer when they start to look less than their best. After a good chop, I fertilize, water, and let them do their thing. And guess what? They bounce back and look fantastic! When you decide to trim, remember the golden pruning rule: never remove more than one-third of the plant at a time. Make sure to cut just above a node, where new growth will emerge. Be mindful of timing, too. Since pruning removes most of the blooms, it’s wise to schedule your trim around important events. If you have a big occasion coming up, hold off until a few weeks before or after so your petunias have time to regrow. As a general rule, avoid pruning if your plants are dry or stressed.
Don’t forget to deadhead regularly. While many modern petunia varieties, like ‘Wave’ and ‘Supertunia,’ are self-cleaning and drop their spent blooms naturally, others, such as grandiflora, ‘Superbissima,’ and trailing varieties, require regular deadheading. Removing faded flowers directs the plant’s energy toward producing more blooms, rather than creating seeds. To find out if your petunias need deadheading, check the plant label or do a little research. If you’ve already planted them, observe whether the old flowers fall off on their own.
Before you start pruning, grab a vase and make a beautiful DIY floral arrangement with the fresh blooms you’ve cut!
