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Data Collection

Researchers collect monthly growth measurements and quality ratings to assess the effects of the different irrigation treatments on plant growth, health, and appearance. Plants are measured and 5-6 quality categories are rated from spring to fall during the deficit season, the second year in the ground. Both parameters taken together are used to evaluate if plant performance has been impacted by irrigation level. Our irrigation rate recommendations are based on the lowest rate or range of rates that yields the best quality ratings. When there is no clear difference between treatments, it means a plant may be used in more than one "hydrozone" in a landscape with the same quality results.

Quality Ratings

Researchers rate plant health and aesthetics at least once per month during the deficit season to assess irrigation treatment effects on plant health and appearance. The categories rated are foliage quality, floral quantity, pest tolerance, disease resistance, vigor, and overall appearance.

Researchers evaluate floral quantity and overall appearance twice per month if the plant is flowering during the deficit irrigation treatments. This practice gives a more detailed record of the plants’ bloom cycle and the effect of flowering on the appearance.

The overall appearance (OA) rating is a measure of the individual plant’s "WOW factor." The OA category in our trial is not the sum of the other factors rated, but rather an assessment of how the plant as a whole is performing in the landscape.

Growth Measurements

Researchers collect monthly length, width, and height measurements during the deficit season. These measurements are used to create a plant growth index (PGI) and relative plant growth index (RPGI), which allows researchers to compare plant growth between treatments.


Researchers collecting plant measurements(SK Reid)


Researchers use the following rubric to evaluate plant material in the trials. The definitions for each measurement are general rather than species or genera specific to allow for application to a wide range of plant material. For example, spent blooms on a rose could negatively impact the plant’s appearance, since they could detract from the beauty of the shrub; spent flower heads (seed heads) on a grass are a desired feature that would improve the overall appearance of the plant. 

RATING 1 2 3 4 5
Foliage unacceptable; close to dead unacceptable; moderate damage to most of the plant or major damage to more than 25%; plant is declining and may not recover; may be  extremely non-uniform acceptable but not its best; non-uniform; minor damage to all leaves that is less evident from a distance, or severe damage to no more than 25% of plant very good; same as 5 except for minor tip burn, edge damage, or minor damage to only a few leaves that does not much affect the overall appearance perfect to excellent; plant is in full leaf with no signs of leaf burn, disease or insect damage, and has an appealing shape and uniformity
Flowering 1 bloom open to 20% in bloom 21-40% of plant in bloom 41-60% of plant in bloom 61-80% of plant in bloom full, glorious bloom; the height of bloom  for the species
Fruiting 1 fruit to 20% of the plant covered with fruit 21-40% of the plant covered with fruit 41-60% of the plant covered with fruit 61-80% of the plant covered with fruit loaded with fruit, the plant has reached full fruit coverage
Pest Tolerance/ Disease Resistance severely damaged and probably dying (>75% affected) major damage ; appearance unacceptable (51-75%) minor damage to many of the leaves or flowers; appearance still acceptable from a distance (25-50%) minor to moderate damage to one or two leaves or stems, or only very minor damage to a few leaves (<25%) no visible damage
Vigor Plant is barely alive; close to death Plant is very small for the species or unhealthy, and declining Plant is surviving and healthy, but not pushing out much new growth, if any pushing out new growth from many growing points pushing out a lot of new growth from every growing point
Overall Appearance completely unacceptable and not likely to improve unacceptable for any of the above reasons Acceptable but nothing special; may be past or not quite to its prime; might be better if more uniform; may be described as an ‘okay’ plant. a very attractive plant; may be a 5 when in bloom, or just a very nice species that lacks the WOW factor or is not quite at its prime An impressive plant; everything works together: flowers (if present), leaves, the shape and condition of the plant are all very appealing.  It has the WOW factor that makes it an attractive garden plant, even if each individual factor isn’t perfect.


Participants at the Open Houses use a streamlined version of the rubric, evaluating only Foliage Quality, Floral Quantity and Overall Appearance.