Methods
Bed Preparation and Planting
A 10,000 sq. ft. area behind the Fisher Greenhouse was tilled in the spring before planting. The soil was not amended, and the beds were mulched prior to planting with a 3-inch layer of wood chips.
Staff and volunteers planted the selections on May 20. Seven plants of each variety were planted 1 ft. apart in rows, with 24-inch or 36-inch spacing between rows depending on cultivar. The rows were organized into seven beds, each measuring 8 ft. by 100 ft.
The plant selections were organized in alphabetical order by botanical name, and identified by white labels listing their botanical name, cultivar, and supplier.
Maintenance
Once established, the Trial Garden received minimal maintenance. Staff irrigated the beds for the first two weeks and applied an all-purpose soluble fertilizer (21-5-20) at planting and during the first two weeks. No supplemental watering or fertilizer was provided for the remainder of the summer, nor were insecticides or fungicides applied. Staff hand weeded as necessary. None of the trial plants were deadheaded or pruned.
Evaluations
The Horticulture Manager at UDBG evaluated the Trial Garden plants every other week from July 1 through September 30. For each date, plants were awarded three scores: one for flowering, one for foliage, and one for habit. Habit evaluates how uniformly the plants grow. If all seven plants differ in size, the score is lower; if they are all very similar in size, the score is higher. Habit also takes into account how well the plant maintains its form: does it splay over time, or does it stand upright and hold its shape throughout the season? The overall scores for flowers and foliage represent the average of all individual scores for each category. Woody plant material is scored with one overall category, taking into consideration the three categories used for annuals as well as the overall health and appearance of the plants.
Weather
The following charts were generated from weather information obtained from Delaware Environmental Observing System Network at the University of Delaware Farm.
Results
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 2.5 | |
| 7/15/24 | 3 | |
| 7/29/24 | 3.5 | |
| 8/12/24 | 4 | |
| 8/26/24 | 3 | |
| 9/9/24 | 3 | |
| 9/23/24 | 3 | |
| 6/23/25 | 3 | |
| 7/7/25 | 4.5 | |
| 7/21/25 | 4.5 | Peak Bloom |
| 8/4/25 | 4 | |
| 8/18/25 | 4 | |
| 9/2/25 | 4 | |
| 9/15/25 | 3.5 | End of Bloom |
| 9/29/25 | 3.5 | |
| Average Score: | 3.53 |
This Hydrangea performed much better in its second season. There were minimal foliage issues, and it performed well in full sun, even during periods of drought. It produced a great flower set from mid-July through mid-September.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 4 | |
| 7/15/24 | 4 | |
| 7/29/24 | 4 | |
| 8/12/24 | 3.5 | |
| 8/26/24 | 4 | |
| 9/9/24 | 4 | Huge flowerheads |
| 9/23/24 | 3.5 | Drought effects |
| 6/23/25 | 3 | |
| 7/7/25 | 4.5 | |
| 7/21/25 | 4.5 | |
| 8/4/25 | 5 | Peak flowering |
| 8/18/25 | 4.5 | |
| 9/2/25 | 4.5 | |
| 9/15/25 | 4.5 | |
| 9/29/25 | 4 | |
| Average Score: | 4.1 |
By far the runaway victor for Hydrangea paniculata in this trial. The plant survived and performed well through extended drought periods in the first year. Huge flowers covered the petite plant, creating an impressive display that lasted nearly 10 weeks during the summer.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 3 | |
| 7/15/24 | 2.5 | |
| 7/29/24 | 3 | |
| 8/12/24 | 3 | |
| 8/26/24 | 2.5 | Drought stress |
| 9/9/24 | 2.5 | |
| 9/23/24 | 2 | |
| 6/23/25 | 3.5 | |
| 7/7/25 | 3.5 | |
| 7/21/25 | 3.5 | Peak flowers, middle of the road flowers |
| 8/4/25 | 3 | |
| 8/18/25 | 3 | |
| 9/2/25 | 2.5 | Severe defoliation |
| 9/15/25 | 2.5 | |
| 9/29/25 | 2.5 | |
| Average Score: | 2.9 |
This Hydrangea struggled over its two-year trial. It experienced defoliation in both seasons, as well as some sun scorch, and when in flower, it was a middling display at best.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 3 | |
| 7/15/24 | 4 | |
| 7/29/24 | 3.5 | |
| 8/12/24 | 3 | |
| 8/26/24 | 3 | |
| 9/9/24 | 2.5 | Slowed growth, assumed from drought |
| 9/23/24 | 2.5 | |
| 6/23/25 | 4 | |
| 7/7/25 | 4 | |
| 7/21/25 | 4 | |
| 8/4/25 | 4.5 | Strong new growth, good form |
| 8/18/25 | 4 | |
| 9/2/25 | 4 | |
| 9/15/25 | 3.5 | |
| 9/29/25 | 3.5 | |
| Average Score: | 3.47 |
Plant displayed small amounts of growth, but good form in the first season. As the second season progressed, much stronger growth was observed as well as retained good form. No disease or pest issues observed.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 3.5 | |
| 7/15/24 | 3.5 | |
| 7/29/24 | 3.5 | |
| 8/12/24 | 3.5 | |
| 8/26/24 | 3 | |
| 9/9/24 | 3 | |
| 9/23/24 | 3 | |
| 6/23/25 | 3 | |
| 7/7/25 | 4 | |
| 7/21/25 | 4 | |
| 8/4/25 | 4 | |
| 8/18/25 | 3 | |
| 9/2/25 | 3.5 | |
| 9/15/25 | 3 | |
| 9/29/25 | 3 | |
| Average Score: | 3.37 |
Compared to Gem Box®, this plant performed at a decent, but slower pace. This variety grew steadily and slowly in the second season after some slight drought damage in the first season.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 2 | |
| 7/15/24 | 2 | |
| 7/29/24 | 2.5 | |
| 8/12/24 | 2.5 | |
| 8/26/24 | 1.5 | |
| 9/9/24 | 1 | Deer browse |
| 9/23/24 | 1 | 1 Dead |
| 6/23/25 | 0 | All plants did not survive Zone 7a Winter |
| 7/7/25 | 0 | |
| 7/21/25 | 0 | |
| 8/4/25 | 0 | |
| 8/18/25 | 0 | |
| 9/2/25 | 0 | |
| 9/15/25 | 0 | |
| 9/29/25 | 0 | |
| Average Score: | 0.83 |
This variety did not perform well and declined soon after establishment. The plants failed to survive into the second growing season, even though the winter was milder than usual for this area.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 2.5 | Sun Scorch |
| 7/15/24 | 2 | |
| 7/29/24 | 2 | |
| 8/12/24 | 2 | |
| 8/26/24 | 2 | |
| 9/9/24 | 1.5 | Worsening Sun Scorch |
| 9/23/24 | 2 | |
| 6/23/25 | 3 | One died over winter |
| 7/7/25 | 4 | |
| 7/21/25 | 4 | |
| 8/4/25 | 4 | |
| 8/18/25 | 3 | Slight Sun Scorch |
| 9/2/25 | 3.5 | |
| 9/15/25 | 3 | |
| 9/29/25 | 3 | |
| Average Score: | 2.77 |
The plant displayed a small amount of growth over its two growing seasons. While garden visitors enjoyed the variegated foliage, the sun scorch significantly detracted from the aesthetics of this Weigela.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 4 | |
| 7/15/24 | 2.5 | |
| 7/29/24 | 2.5 | |
| 8/12/24 | 2.5 | Sun Scorch |
| 8/26/24 | 2.5 | |
| 9/9/24 | 2 | Odd growth habit |
| 9/23/24 | 3 | |
| 6/23/25 | 3 | |
| 7/7/25 | 3.5 | Mild Sun Scorch |
| 7/21/25 | 4 | New flush of growth |
| 8/4/25 | 4 | |
| 8/18/25 | 3.5 | |
| 9/2/25 | 4 | Rebloom Start |
| 9/15/25 | 4.5 | Rebloom Finish |
| 9/29/25 | 4 | |
| Average Score: | 3.3 |
A very nice Weigela, this plant developed a small amount of sun scorch in the second season but also produced a nice spurt of rebloom that year.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 3.5 | |
| 7/15/24 | 3.5 | |
| 7/29/24 | 4 | |
| 8/12/24 | 3.5 | |
| 8/26/24 | 3.5 | |
| 9/9/24 | 3.5 | Rebloom start and new flush of growth |
| 9/23/24 | 3.5 | |
| 6/23/25 | 4.5 | Vigorous new growth |
| 7/7/25 | 4.5 | |
| 7/21/25 | 4 | |
| 8/4/25 | 5 | |
| 8/18/25 | 5 | Rebloom start |
| 9/2/25 | 5 | |
| 9/15/25 | 5 | |
| 9/29/25 | 5 | Rebloom finishing |
| Average Score: | 4.2 |
The clear winner of the Weigela trials in the eyes of the UDBG team. The plant showed no foliage issues during either growing season and produced a substantial amount of new growth, reaching 3.5′ tall by the end of year two. Its rebloom period lasted a long time and provided an excellent display for both photos and pollinators.
| Date | Score | Notes |
|---|---|---|
| 7/1/24 | 4 | |
| 7/15/24 | 3 | |
| 7/29/24 | 3.5 | |
| 8/12/24 | 3 | |
| 8/26/24 | 3.5 | |
| 9/9/24 | 2.5 | Sun Scorch |
| 9/23/24 | 3 | |
| 6/23/25 | 4 | |
| 7/7/25 | 4.5 | |
| 7/21/25 | 4 | |
| 8/4/25 | 4.5 | |
| 8/18/25 | 4.5 | Rebloom start |
| 9/2/25 | 4.5 | Rebloom finish |
| 9/15/25 | 4 | |
| 9/29/25 | 4 | |
| Average Score: | 3.77 |
Another great Weigela selection emerged from this group of UDBG trials. Its maroon foliage and white flowers helped it stand out above the competition. While the plant showed a slight tinge of sun scorch by the end of its first season, this issue did not appear in year two, which instead featured a good rebloom period and vigorous growth.
| Scientific Name | Common Name |
| Hydrangea paniculata | Panicle Hydrangea |
| Ilex glabra | Inkberry Holly |
| xPyracomeles | Pyracantha/Osteomeles hybrid |
| Weigela florida | Old Fashioned Weigela |
