Trial Gardens

Trial gardens are specialized research gardens where new and improved plant varieties are grown, observed, and evaluated. These gardens serve as living laboratories; testing how different cultivars perform under real-world conditions such as heat, humidity, rainfall, and soil variation. The goal is to determine which plants truly thrive in the landscape, not just in controlled greenhouse environments.

In these gardens, newly developed annuals and perennials are planted each Spring and monitored throughout the growing season. Researchers and horticultural experts record data on everything from growth habit and flower color retention to resistance against pests and diseases. By the end of the season, only the most reliable and beautiful performers earn top marks.

Leading Trial Gardens in the United States

There are dozens of trial gardens across the country, but a few stand out as leaders in independent, unbiased testing. Among the most respected are:

  • Penn State University (PSU) Trial Gardens – Located in University Park, Pennsylvania, this garden is known for its rigorous data collection and precise scoring system. The PSU trials provide numerical ratings out of 5, making it easy to compare varieties year after year. They evaluate 500-700+ varieties each year, including shade evaluations.

  • University of Georgia (UGA) Trial Gardens – Situated in Athens, Georgia, this garden is one of the premier trialing locations in the Southeast. Its challenging hot, humid climate provides an excellent test for summer endurance, separating true performers from those that fade by midsummer. They evaluate 300-500 varieties each year.

  • Raker-Roberta’s Trial Gardens – Located in Litchfield, Michigan, Raker conducts extensive trials across thousands of annual and perennial varieties. Their data is widely used by growers, retailers, and breeders alike to gauge commercial potential. They evaluate more than 3000 varieties each year, and have recently added shade gardens and cut flower gardens.

These three trial gardens not only incorporated quantitative evaluation in their trials, but also make their data publicly available to industry professionals and consumers alike. And, because all three evaluate based on a 5.0 scale, their data are comparable.

Other Plant Testing Organizations

Several other organizations also provide extremely useful information, through their qualitative vs quantitative evaluations. For example, famous for its intense Texas heat trials, the Dallas Arboretum tests how well plants hold up under extreme summer conditions. A plant that thrives here can thrive almost anywhere in the South. Between 3,000 - 5,000 plants are trialed annually with awards such as “Flameproof” defining the best of the best. And, their data are publicly available on the internet.

Similarly, the International Perennial Society, All America Selections, and the Royal Horticultural Society all provide reliable trials with publicly available summaries of their winners. What makes these trial gardens so valuable is their independence. They are not run by plant breeders or marketing groups—which ensures that ratings are unbiased, data-driven, and reflective of real-world garden performance.

How Plants Are Rated

Each US trial garden has its own methodology, but most follow a consistent seasonal pattern:

  • Planting: In the US, trials begin in May when new varieties are planted under standardized conditions. Note that in the South, plantings may begin in April, but in Northern climates, planting generally begin after Mother’s Day when all threat of frost has passed.

  • Observation: Plants are monitored throughout summer for factors including uniformity, growth, bloom coverage, foliage appearance, and pest and disease resistance.

  • Evaluation: Ratings are typically assigned from July through August. If we are lucky, the evaluation period may begin as early as June and extend into September or even October, which is invaluable when determining viability in extended growing seasons such as in the South.  

Plants in these trials are given top-notch treatment, with regular water, fertilizer and pest deterrents, which means that their performance should exceed the performance in normal homeowners’ gardens which may be subject to neglect … from time to time.

At Penn State, Raker Roberta’s, and UGA, numerical ratings are assigned on a 5-point scale:

  • 5.0 – Exceptional performance

  • 4.5–4.9 – Excellent

  • 4.0–4.4 – Very good

  • Below 4.0 – Average performance

Regardless of the system, these independent evaluations are trusted by professional growers, garden centers, and landscapers to identify the best varieties each year.

Why Trial Gardens Matter

Trial gardens are more than just research plots—they are the bridge between plant breeding innovation and real-world gardening success. Every season, they help the horticultural community discover which plants can truly handle heat, humidity, and time. Their work ensures that what you see in our garden center or online store isn’t just a pretty face—it’s a performer.

For gardeners, trial gardens offer peace of mind. The ratings behind each plant represent hundreds of hours of observation and data collection. That’s why we trust them—and why you can trust us. The big question is…

Why buy an average performer when you can purchase an exceptional performer?

How We Use Trial Gardens at Garden Delivery

At Garden Delivery, we rely heavily on data from these independent trial gardens to guide our plant selections. Additionally, for several years, we have performed our own independent test trials in our own gardens. Our goal is to bring you varieties that have not only look good in photos, but have proven themselves through months of heat, rain, and real-world conditions.

It is important that all the plants we chose have the following characteristics:

  • Hardiness – Plants must endure challenging conditions, including heat, humidity, and periods of excessive rainfall.

  • Bloom Proficiency – A consistent and abundant floral display is essential throughout the season.

  • Overall Aesthetic Appeal – In addition to blooms, uniform growth and vibrant foliage contribute to visual impact.

  • Resilience - Unlike trial gardens that baby their plants, homeowners are going to neglect their plants from time to time so a plant must be able to rebound from neglect or thrive without attention.

  • Longevity – Arguably the most critical trait. Many plants peak in June—few hold their brilliance through September. But in the South, we demand more—our landscapes need to shine through November.

With these factors in mind, here’s how we use trial data in our selection process of which plants to grow each year:

  • Annuals: We primarily select varieties that score 4.8 out of 5 or higher in independent trials. These plants are the cream of the crop—long-lasting bloomers that start in the early spring and continue performing deep into fall often until first frost. We’ve found that annual plants with ratings less than 4.8 start to burn out in September and are often gone by October.

  • Perennials: We look for varieties rated 4.0 out of 5 or higher, ensuring that every perennial we offer has demonstrated strong vigor and seasonal reliability. Because most perennials are only seasonal bloomers, their lack of flowering often lowers their overall scores, thus resulting in our lower range.

Occasionally, we make exceptions for varieties that show exceptional uniqueness or customer demand, even if they fall just below our standard. For example, Angelonia AngelFlare Black —with a trial rating of 4.7/5—is one we proudly carry because of its unique nearly black blooms and proven popularity with gardeners. Note, however, that in our independent testing of this plant, it grew and flowered beautifully from April through November, which merits a 5.0 in our book.

We believe that trial performance is one of the most reliable indicators of garden success, which is why it plays such a central role in our selection process. When you shop at Garden Delivery, you’re choosing plants that have already been tested by experts and also some have been tested in our own trial gardens, and they have been proven to perform.