Petunias

How much does Gerdes love petunias? Let her count the ways: "Petunias come in all colors from pastels to bold, bright hues, have a mounding or trailing habit, and can stand alone or mix well with other annuals," she says. Even better, these container favorites keep going all summer. Just deadhead them once in a while, water consistently, and consider fertilizing for even more blooms.

Gerdes's top petunia picks are those from the Wave series. 'Easy Wave' has larger flowers, great for cascading over a hanging basket or filling up a large pot. For smaller containers, she recommends the more compact 'Shock Wave,' whose flowers are slightly smaller (the petals of varieties like 'Rose Vein and 'Pink Vein' even have striking veining.)

Impatiens

Plant this classic flower in a pot or basket, and it will put on a nonstop show until frost. A perennial that's grown as an annual in most climates, impatiens have a classic beauty and are known for their quick growth. Even better, says Gerdes, "they're one of the few plants that blooms reliably in the shade."

Flower colors can range from soft pink to bright orange, as well as white. Gerdes has found the 'Beacon' series to be an especially strong performer in the Test Garden, blooming all summer long and resistant to disease. She's also a fan of 'New Guinea' impatiens, which take take full sun or full shade and come in a wide variety of flower colors and leaf shapes.

Begonia

In the wide world of begonias, Gerdes favors the trailing varieties for the way their flowers and foliage spill abundantly from containers. "They're ideal for hanging baskets or window boxes," she says. Whatever your garden scheme, there's a trailing begonia that will fit right in: Blooms can be single or double, foliage ranges from green to bronze, and plants can take part shade to full sun.

One of her favorites is Begonia boliviensis, particularly the 'Groovy' series for its "graceful, trailing blooms with slender, pointed leaves," she says. They come in several colors such as red, orange, yellow, and salmon (shown here). She also regularly pots up 'Canary Wings' angelwing begonia for its clusters of bright red flowers against chartreuse leaves.

Dianthus

Dianthus (aka "pinks") thrives in bright, dry conditions, producing loads of sweet, carnation-like blooms atop low-growing bluish or gray-green foliage. As a bonus, they attract pollinators and often have a pleasant fragrance. Just be sure to give plants good drainage and don't overwater, Gerdes advises. "And deadhead to keep flowers coming," she says.

Of the many dianthus varieties she's planted up in terra cotta pots in the Test Garden, Gerdes says the 'Oscar' series stands out for its heat and frost tolerance, and "charming double blooms in solid and bicolor shades."

Celosia

Mixed containers often work best with a thriller, filler, and spiller plant. Plumed and wheat types of celosia clearly fall into the thriller category, producing showstopping, feathery spikes of flowers. "They add texture and vertical interest to mixed containers, plus they're a fun cut for bouquets," says Gerdes.

Celosia grows easily from seed, and does best in full sun with well-drained soil. Gerdes recommends pinching plants back once in a while to increase branching. Seed companies and nurseries sell a huge variety of celosia but Gerdes says you can't go wrong with the 'Flamma' series, an All-America Selections winner that comes both in pink and orange.

Salvia

This sun-loving plant has a rich range of flower colors, but also brings your garden to life with all the hummingbirds and pollinators it attracts. Plus, in sizes both large and more compact, "it's great solo or as a mixer in large pots," says Gerdes. Deadhead regularly to keep the flowers coming all summer.

For containers, she finds herself regularly opting for salvia from the 'Bodacious' series, which are compact and have repeating blooms in deeply saturated colors. They'e planted as annuals in most regions, and as tender perennials in warmer climates.

Pentas

Pentas's flower clusters look cheerful in a container—and their abundant nectar makes them irresistible to pollinators. "Mix several colors in one pot and watch the butterflies come," says Gerdes. The star-shaped flowers come in pink, purple, red, and white. An annual in most climates, it thrives in full sun with regular watering.

While many pentas varieties have upright habits, Gerdes has recently fallen for a new cascading hybrid called 'Graffiti Falls'. "It's perfect for hanging baskets, creating a lush spill of falling stars," she says.