Top Annual Plant Picks from the 2025 Cumberland County Flower Trials

The Penn State Master Gardeners of Cumberland County trial annual plants, newly introduced in the retail market, at the Trial and Idea Demonstration Garden at the corner of Army Heritage Drive and Claremont Road in Carlisle. The full-sun garden tests the annuals' ability to adapt to growing conditions in south central Pennsylvania gardens. In addition to the trial garden, there are five more garden beds on the site featuring perennials, shrubs, native pollinators, and mature trees.

A team of Master Gardeners tend the annuals planted in groups on a weekly basis and evaluate plant performance every other week in four categories—uniformity, foliage, flower, and growth. Plants are regularly watered and deadheaded, as needed, but not supplemented with commercial fertilizers, fungicides, or insecticides.

The 2025 best performers include cultivars of petunia, ageratum, marigold, and celosia.

Petunia

TwoSupertunia® petunia hybrids made a big splash in the garden this year. Supertunia® Tiara Blue and Supertunia® Tiara Pink are sterile hybrids that require no deadheading to keep them blooming all summer long. Both Tiara Blue and Tiara Pink feature medium-sized flowers with bright white centers surrounded by tones of purple-blue or pink, respectively. These vigorous, low-growing, long-blooming, and heat-tolerant plants, which require no deadheading, are a great choice for beds, containers, hanging baskets, or to serve as a groundcover. The blue petunia met the maximum expected spread of 24 inches, while the pink grew to twice that size.

Ageratum

Aptly named, monarch butterflies and people alike found the 'Monarch Magic' annual ageratum to be a spectacular plant. It was common to see four or more Monarch butterflies enjoying the nectar. A low-maintenance plant, this beauty requires no deadheading to produce continual blooms. Drought-tolerant with a vigorous spreading habit, it quickly fills the garden with purple-blue flowers, as well as butterflies and other pollinators. Growing to more than double the expected size, it delighted us with flowers and butterflies well into the fall.

Marigold

The 'Milli Vanilli' French marigold delights gardeners with large, semi-double, anemone-style flowers in an intense yellow hue. It has excellent heat tolerance and is ready to flower in just seven to ten weeks from seed sowing. This marigold is an economical way to add a sunny spot to the garden. Compact plants hold a uniform shape throughout the season, and common to marigolds, happily continue to produce flowers through the first light frosts. It is a favorite of ours, but not of the bunnies.

Celosia

Another compact selection for the garden, 'Burning Embers' celosia grows to about ten inches in height. This well-branched plant displays an abundance of red plumes above bronze foliage with pink veins that retain their bright color throughout the season. This cultivar continued to produce masses of plumes through the end of October while retaining its bronze-red color profile. While it is a nice color companion for 'Milli Vanilli' in the garden, it is equally great in containers and borders. Try planting them in a group for a wave of "burning embers" in your garden.

An Unusual Annual

While not a top performer, Kangaroo Paws 'Kanga Cherry' is an unusual selection.Native to southwestern Australia's eucalyptus forests and coastal regions, Kangaroo Paws display fuzzy paw-like flowers on upright stems complete with claws when the buds open. This drought-resistant annual is worth a try to add unique interest in the garden.

The full review of annuals trialed by the Cumberland County Trial and Idea Garden can be viewed on the website for the Penn State Master Gardeners of Cumberland County.