Grow Show-Stopping Giant Petunias: 7 Essential Steps

Petunias are a must-have annual, especially in hanging baskets. They look stunning in flower, but over time, those flowers can become lackluster.

Luckily, with the right techniques, petunias can stay spectacular all season, creating cascading walls of color that spill dramatically from containers visible from across the yard. The techniques that create show-stopping giant petunias often require more initial effort, but the results are definitely worth it. Follow these 7 tips to grow massive petunias this season.

Start with Large Containers

Petunias are often grown in containers, particularly ones that are too small. But it’s important to remember that container size directly affects growth potential. Small containers restrict root development and limit the plant's ability to support extensive top growth and continuous flowering. They will adapt, but the situation is not ideal if you want giant petunias.

Larger containers create even more dramatic displays by providing root space that supports truly massive top growth. The plants need room to expand, so don’t think a larger container just means you should plant more seeds. A little extra space (but not too much) will lead to much better flowers.

Shallow containers dry out quickly and limit root development that supports vigorous growth. Aim for containers or patio planters at least 12 inches deep to provide adequate root space. Drainage is also critical. Ensure multiple drainage holes to prevent waterlogging, which kills petunias faster than almost any other problem.

Choose the Right Varieties

Not all petunias have equal potential for giant flowers. Grandiflora types produce larger individual flowers, while multiflora varieties offer better spreading potential with abundant smaller blooms. There are many unique varieties to choose from, so it’s important to match the type to your ultimate goal.

The Supertunia combines the best traits of a spreading habit with larger flower size. These varieties maintain vigorous growth while producing substantial blooms that create impressive visual impact. For giant petunias in many wonderful colors, this is a choice you can’t go wrong with.

Avoid compact varieties if size is your goal. These are bred for controlled growth that works against the sprawling habit needed for show-stopping results. Research specific varieties before purchasing and choose seeds over potted plants for complete control over growing conditions.

Feed Often

Giant petunias are already quite heavy feeders in pots, but the continuous blooming and extensive growth demand consistent feeding to maintain peak performance. You may sacrifice other aspects of growth and length of the season, but flowers will not be one of them.

Frequent watering in pots means fewer nutrients over time. That doesn’t mean you should water less, but that you need to replace those nutrients to maintain those giant petunias you worked so hard for.

Apply a liquid fertilizer every two weeks or so during peak growing season to maximize flowering potential. Balanced fertilizers work well early in the season while the plants are establishing, but switch to ones with higher phosphorus content once heavy flowering begins.

Keep an eye on the plant response and adjust feeding accordingly. Plants with excessive vegetative growth might need reduced nitrogen levels. Regular feeding is important, but it is possible to overdo it.

Pinch Stems

Strategic pinching creates the branching structure needed for giant petunias. Although you may not want to get rid of healthy growth, regular pinching does lead to better performance later on.

Pinch growing tips when plants reach a few inches tall to encourage branching from the base. Continue pinching throughout early summer to encourage additional branching. Each creates two or three new growing points, increasing the plant's flowering potential as the season progresses.

Remove spent flowers during establishment. Initially, you want more vegetative growth over seed production. Once plants reach the size you were hoping for, you can ease up on maintenance to enjoy the giant petunia blooms.

Water Consistently

Petunias in large containers need more water than plants in the ground. Inadequate moisture limits growth and flowering, while inconsistent watering stresses plants and reduces performance.

If you’re too busy to water daily, install automatic watering systems for large petunia containers. These provide consistent moisture without the daily commitment hand watering requires during peak summer heat. Plus, you can reuse them season after season for different plants, depending on what you’re growing that year.

Check soil moisture daily during hot weather. Large containers can still dry out faster than expected despite their size. The root systems use enormous amounts of water during peak growing periods, particularly when they’re working to make giant petunia flowers.

Water until excess moisture drains from the container to ensure complete soil saturation. Also make sure you’re watering around all sides of the container. Shallow watering that wets only the soil surface makes plants more susceptible to drought stress.

Morning watering works best for petunias, giving plants time to absorb moisture before afternoon heat peaks. You may need to water again in the evening in hot weather if you want to sustain your giant petunias.

Choose the Ideal Location

Location determines how impressive your giant petunias become. Not only from a growth perspective, but also how you enjoy them.

First (and arguably most important) is visibility. Elevated positions like hanging baskets showcase trailing petunias most effectively. Raised planters or window boxes allow cascading growth that catches the eye at the right level.

Consider backdrop colors and textures when positioning giant petunias. Dark backgrounds make colorful flowers more prominent, while competing colors in the background diminish visual impact.

Then there’s care, starting with sunlight. Morning sun with afternoon shade often produces better results than full sun locations if you live in an area with intense summer heat. Petunias that struggle in afternoon sun won’t ever look their best, even if the other maintenance tasks are all up to date.

Also consider wind, especially if you’re growing on an exposed patio or balcony. A light breeze is fine, but consistent high winds will stress plants.

Don’t Give Up On Maintenance

What starts as a spectacular giant petunia can quickly deteriorate without consistent maintenance. Mid-season trimming rejuvenates plants that become leggy. Cut back by one-third during mid-summer to force renewed flowering that extends displays into fall.

Disease prevention also becomes more critical with dense petunia growth that restricts air circulation. Remove any diseased foliage immediately and ensure adequate spacing between displays. Plus, pests can quickly damage months of careful growing effort. Early detection and treatment in either case prevent minor problems from becoming display-ruining infestations.

Other protective tricks, like temporary shade during heat waves or wind protection during storms, limit damage that takes weeks to recover from. To ensure your giant petunias last as long as possible, don’t skip the extra steps.