Plant Trials | Mt. Cuba Center

Subscribe to the Trial Garden Mailing List

Year 1

Heuchera Evaluation 2012-2014

Heuchera, also known as coral bells or alumroot, are currently a favorite of gardeners everywhere. In 2012 Mt. Cuba Center began an evaluation of Heuchera where plants were chosen based on having H. americana or H. villosa as one of their parents. These east coast natives are thought to be better suited to mid-Atlantic growing conditions than species from other regions of the country. With 86 cultivars being examined, we have barely scratched the surface of the total number available in the trade. How is a gardener supposed to decide from such an overwhelming selection? In addition, many cultivars are advertised as being tolerant of full sun growing conditions. This may be true in some regions, but Heuchera are generally thought of as shade-loving plants in the mid-Atlantic. Intensive breeding work has created a plethora of color combinations, but often to the detriment of floral display. These topics and more are being examined in our three-year trial of native Heuchera and their hybrids. The results of this evaluation will produce recommendations for plants best suited to the mid-Atlantic region. In the meantime, check back regularly for insights, images and trial updates.

The interim rating speaks only to the performance of a plant in that particular year. Each plant will receive a final rating only after the entire three-year trial period is finished.

Some of the top rated Heuchera cultivars of 2012 include 'Apple Crisp', 'Berry Smoothie', 'Berry Marmalade', 'Cajun Fire', 'Purple Petticoats', 'Dale's Strain', 'Obsidian', 'Guardian Angel', and 'Spellbound'.

Description of Evaluation Project

Mt. Cuba Center is located near Wilmington, DE, (USDA Hardiness Zone7A/6B). Five plants of each taxon are grown in a shade structure as part of a 15,000 sq. ft. trial garden. The structure is furnished with a shade cloth that blocks 60% of the natural sunlight. One plant of each taxon is also grown in full sun in order to determine its tolerance to these conditions. The garden is protected from rodents by a 4’ tall wire fence within a 100-acre garden protected by a 10’ tall deer exclusion fence. The clay-loam soil in the trial garden has an average pH of 6.5.

The Trial Garden is maintained with the home gardener in mind. Plants are watered as needed during the first year in order to get them established. After that, they are left on their own. Pesticides are not used unless there is a serious threat to the trial’s survivability.

Perennial plant trials at Mt. Cuba Center typically run for three years. If a plant dies during the first year of evaluation it is replanted in the spring of the second year. We look closely at foliage color, size, floral display, and sun tolerance. We also evaluate plant habit, with higher marks being given to plants with a uniformly mounded and dense habit. Lower scores are assigned to plants that display poor vigor and open habits. Disease and insect resistance are also carefully considered. In our Heuchera trial, these attributes are evaluated to create three ratings; overall plant health/appearance, floral, and sun tolerance.

Rating System

Our numerical rating system ranges from one to five and can be interpreted as follows:

      1. Poor
      2. Below Average
      3. Average
      4. Good
      5. Excellent

Ratings are made during weekly observations. The following rubric is used in assigning ratings for overall plant health and appearance.

      1. Dying or near death.
      2. Very open habit or damage on more than 25% of foliage.
      3. Slightly open habit and may have a small amount of damaged foliage.
      4. Vigorous and healthy, with a habit that is dense but not perfectly uniform.
      5. Habit is perfectly dense and mounding. No disease or foliage problems.

The following rubric is used when assigning ratings for floral display.

      1. Inconspicuous flowers. Display is unattractive and would be best if removed.
      3. Floral display does not detract from the aesthetic appeal.
          Flowers are not proportional to plant size or do not compliment foliage color.
      5. Flowers are numerous and complimentary to the foliage color.
          Floral display is attractive and can be thought of as a selling point.

The following rubric is used when assigning ratings for sun tolerance.

      1. Majority of foliage is burnt. Poor growth/vigor.
      2. Moderate foliage burning, slight bleaching or burning on new growth.
      3. Leaf discoloration/bleaching and small burnt spots or leaf margins.
      4. Mild discoloration/bleaching. Slight sun damage on lower leaves only.
      5. No sun damage. Looks similar to plants grown in shade.

Below you will see data collected for 85 cultivars of Heuchera. You may look up a specific plant by scrolling through the alphabetical list of botanical names on the left side of the page, or browse by name and picture on the right side of the page. Either way you will find the botanical name, the common name, and an interim rating.

The interim rating speaks only to the performance of a plant in that particular year. Each plant will receive a final rating only after the entire three-year trial period is finished.

Year 1

Annual Coreopsis Evaluation 2012-2013

Our evaluation of 26 cultivars of annual Coreopsis, or tickseed, is part of our larger trial of the genus Coreopsis. These cultivars are judged on slightly different criteria than the perennial types. As annuals in regions colder than USDA Zone 8/9, it is expected that each plant will create a colorful landscape impact over a long period of time, generally all summer. Therefore, floral display and longevity are very critical. With this trial, we hope to determine if these native annuals have merit as alternatives to more traditional bedding plants.

The interim rating speaks only to the performance of a plant in that particular year. Each plant will receive a final rating only after the trial period is finished.

Some of the top performing annual Coreopsis cultivars of 2012 include 'Jive', 'Salsa', 'Golden Dream', 'Cha Cha Cha', 'Pineapple Pie', and 'RP #1' (Little Penny).

Description of Evaluation Project

Mt. Cuba Center is located near Wilmington, DE, (USDA Hardiness Zone7A/6B). Ten plants of each taxon are grown in full sun in a 15,000 sq. ft. trial garden protected from rodents by a 4’ tall wire fence within a 100-acre garden protected by a 10’ tall deer exclusion fence. The clay-loam soil in the trial garden has an average pH of 6.5.

The Trial Garden is maintained with the home gardener in mind. Plants are initially watered as needed in order to get them established. After that, they are left on their own. Pesticides are not used unless there is a serious threat to the trial’s survivability.

The annual Coreopsis trial is repeated twice in order to insure consistency in performance. We look closely at flower size, color and longevity. We also evaluate plant habit, with higher marks being given to plants with a uniform, sturdy, and upright habit. Lower scores are assigned to plants that are lodging or sprawling. Disease and insect resistance, combined with foliage appearance, are also carefully considered. In our annual Coreopsis trial, all of these attributes are combined to form one numerical rating for each cultivar or species.

Rating System

Our numerical rating system ranges from one to five and can be interpreted as follows:

     1. Poor
     2. Below Average
     3. Average
     4. Good
     5. Excellent

Ratings are made during weekly observations. Using this scale, plants must be in flower to receive a rating of 4 or 5. However, plants that are flowering can receive lower ratings if they are floppy or have significant disease problems. The following is a generalized rubric that we follow when assigning ratings:

     1. Dying or near death.
     2. Poor habit (flopping), disease problems.
     3. Non-flowering healthy plants. Or minor problems with habit and disease on flowering plants.
     4. Flower coverage 20-60% and a strong upright habit. No disease.
     5. Excellent habit. Flowers cover 60% of the plant or more. No disease.

Below you will see data collected for the 26 cultivars of annual Coreopsis. You may look up a specific plant by scrolling through the alphabetical list of botanical names on the left side of the page, or browse by name and picture on the right side of the page. Either way you will find the botanical name, the common name, and an interim rating.

Note: All plants were dead headed in early July to promote fresh blooms for the Trial Garden Grand Opening. This is the reason many plants experienced a dramatic decline in flower coverage in July.

The interim rating speaks only to the performance of a plant in that particular year. Each plant will receive a final rating only after the trial period is finished.

Year 1

Coreopsis Evaluation 2012-2014

Our three-year evaluation of Coreopsis, commonly known as tickseed, was restarted in 2012 after the Trial Garden renovation. This group of plants is one of the most popular, best-selling perennials available today. Clearly, some of the native Coreopsis species deserve broader use in mainstream gardening. At the same time, there is a great deal of confusion among gardeners because some perennial cultivars do not perform as well as advertised. They may be short-lived perennials, or in fact, act like annuals. Sadly, many are also prone to pests and disease. Which are which? Careful evaluation in our Trial Garden will produce recommendations for plants best suited to the mid-Atlantic region. In the meantime, check back regularly for insights, images and trial updates.

These interim ratings speak only to the performance of a plant in that particular year. Each plant will receive a final rating only after the entire three-year trial period is finished.

Some of the top rated Coreopsis cultivars of 2012 include 'Moonbeam', 'Mercury Rising', 'Show Stopper', 'Citrine', and C. helianthoides.

Description of Evaluation Project

Mt. Cuba Center is located near Wilmington, DE, (USDA Hardiness Zone7a/6b). Five plants of each taxon are grown in full sun in a 15,000 sq. ft. trial garden protected from rodents by a 4’ tall wire fence within a 100-acre garden protected by a 10’ tall deer exclusion fence. The clay-loam soil in the trial garden has an average pH of 6.5.

Plants were chosen based on the criteria of being species or selections native to the eastern United States. Plants of hybrid origin were included if at least one parent in their lineage was native to the eastern United States.

Perennial plant trials at Mt. Cuba Center typically run for three years. If a plant dies during the first year of evaluation it is replanted in the spring of the second year. We look closely at flower form, size, color and longevity. We also evaluate plant habit, with higher marks being given to plants with a uniform, sturdy, and upright habit. Lower scores are assigned to plants that are lodging or sprawling. Disease and insect resistance, combined with foliage appearance, are also carefully considered. In our Coreopsis trial, all of these attributes are combined to form one numerical rating for each cultivar or species.

Rating System

Our numerical rating system ranges from one to five and can be interpreted as follows:

1. Poor
2. Below Average
3. Average
4. Very Good
5. Excellent

1. Dying or near death.
2. Poor habit (flopping), disease problems.
3. Non-flowering healthy plants, or minor problems with habit and disease on flowering plants.
4. Flower coverage greater than 50% and a strong upright habit. No disease. Not good enough to be a 5.
5. Excellent habit. Flowers covering most of the plant. No disease.

Many of the Coreopsis species and cultivars struggled during their first year in the garden. The highest rated cultivar only achieved a 3.7 average rating for the season. Almost all of the plants suffered from powdery mildew, and this weighed heavily on the ratings throughout the summer. There was also a slight nutrient deficiency with our soil. During our recent garden renovation, a large amount of organic matter was added to the soil in order to improve drainage. As the organic matter decayed, it used up much of the nitrogen needed by the plants. The added fertility stress certainly affected this year’s performance and measures will be taken to improve those conditions next year.

Below you will see data collected for 10 species of Coreopsis including 55 cultivars and hybrids. You may look up a specific plant by scrolling through the alphabetical list of botanical names on the left side of the page, or browse by name and picture on the right side of the page. Either way you will find the botanical name, the common name, and an interim rating.

The interim rating speaks only to the performance of a plant in that particular year. Each plant will receive a final rating only after the entire three-year trial period is finished.