Jason Smith, Graduate Student; Dr. James E. Klett, Professor and Extension Landscape Horticulturist; Ronda Koski, Research Associate; David Staats, Research Associate
Panoramic view of research site.
Introduction: Drought is a common phenomenon in Colorado, however, in 2002 and 2003 Colorado had the worst drought in 40 years. Municipalities used mainly outdoor water restriction to reduce the demand on a diminishing water supply. These restrictions created a significant impact on landscapes and on many of the green industries that work with those landscapes.
The Green Industries of Colorado created Best Management Practices (BMPs) and one of the goals of BMPs is the conservation and protection of water resources to address inefficient irrigation in the landscape. To understand how much water to apply to a landscape one must first know the water use of the plants in the landscape. The Green Industries of Colorado (aka GreenCo) put together a large list of plants commonly used in landscapes and it is posted on their website at www.greenco.org. Each of these plants are assigned a crop coefficient classification (Table 1). These classifications are based on empirical data, because there is little published work on the water use of most landscape plants.
Estimated Annual Required Irrigation |
Water Use Category |
Percentage of Reference ET (Eto = cool season grass) |
High |
> 100% |
Medium |
50 - 75% |
Low |
25 - 50% |
Very Low |
< 25% |
Table 1:Crop Coefficient classifications from the GreenCO website |
The purpose of this project is to determine the water requirements of 9 shrub species commonly used in Colorado landscapes. Taking numerical data and carrying out a statistical analysis on that data, as opposed to using just field observations, the water requirements of those plants can be more precisely determined. This project started in 2005 and is now in a transition phase as a new graduate student is taking over in order to continue the project. Of the original 10 species used at the beginning of the experiment, 6 will continue to be tested and used, while 4 species have been replaced with new ones. Limited data collection will occur on the new plant species in 2008 until the plants become established. Kentucky bluegrass will be used as a control for determining the short reference Evapotranspiration (ET) rates.
The 10 species of plants used in the study are as follows:
Plant species studied since 2005 |
New plant species |
- Amelanchier sp. (serviceberry) |
- Cornus sericea ‘Isanti’ (Redosier dogwood) |
- Caryopteris incana (blue mist spirea) |
- Hydrangea arborescens (smooth hydrangea) |
- Poa pratensis (Kentucky bluegrass) |
- Physocarpus opulifolius ‘Diablo’ (ninebark) |
- Rhus trilobata (three leaf sumac) |
- Salix purpurea ‘Nana’ (arctic blue willow) |
- Syringa meyeri (Meyer lilac) |
|
- Syringa vulgaris (common lilac) |
|
GreenCo conducted a survey of all of the plants on their website on which category of water use the plants fall under. Table 2 lists the results of the survey of all 10 species of plants that will be used in this experiment.
|
|
Crop Coefficient Classification |
|
|
Region |
Botanic Name |
Common Name |
East Slope |
West Slope |
Mountain |
All Regions |
Amelanchier alnifolia |
Saskatoon Serviceberry |
Low |
Low |
Low |
Low |
Caryopteris incana |
Blue Mist Spirea |
Low |
Low |
Very Low |
Low |
Cornus sericea |
Redosier Dogwood |
Medium |
Medium |
High |
Medium |
Hydrangea arborescens 'Annabelle' |
Annabelle Smooth Hydrangea |
Medium |
Medium |
Medium |
Medium |
Physocarpus opulifolius |
Ninebark |
Low |
Low |
Low |
Low |
Poa pratensis |
Kentucky Bluegrass |
High |
High |
Medium |
High |
Rhus trilobata |
Three-Leaf Sumac |
Very Low |
Low |
Very Low |
Very Low |
Salix purpurea |
Basket Willow |
High |
Medium |
Medium |
Medium |
Syringa meyeri ‘Palibin’ |
Dwarf Korean Lilac |
Low |
Low |
Low |
Low |
Syringa vulgaris |
Common Lilac |
Low |
Low |
Low |
Low |
Table 2:List of plant species and corresponding crop coefficient classification from a survey conducted by the Green Industries of Colorado (GreenCo)
Selected shrubs and turf were planted in plots receiving different levels of irrigation.
Materials and Methods:
The research site is divided into 2 studies; a drought tolerance study and a pot-in-pot lysimeter study.
Drought Tolerance Study:
The drought tolerance study is the infield component of this research project. There are 4 blocks in the drought tolerance study and each of these blocks contains 5 repetitions. Each block receives different percentages of irrigation based on the ET rate of a short reference crop. The percentages chosen for each block are 0%, 25%, 50% and 100%.
Shrub stress is documented by monitoring water deficit and transpiration rates using a pressure chamber made by PMS Instruments. Predawn pressure chamber measurements are taken from 3 of the 10 species of plants to determine plant water potential. The 3 species that measurements are taken from are the serviceberry, three leaf sumac, and common lilac. Basically, gas is injected into a chamber to exert pressure on a sample leaf and the more pressure that is needed to extract the contained water, the more stressed the plant is. The pressure chamber measures the pressure at which a plant must exert to extract water form the soil. Plant water potential is the amount of water available for uptake into the roots. From these measurements plant water deficit can be inferred.
Soil moisture data is collected to determine differences between treatment blocks and determine the efficiency of the irrigation frequency and quality. The Diviner 2000, made by Sentek, is a soil moisture probe that is used in this project. The probe operates by frequency domain reflectometry (FDR) and measures the soil profile at 10 cm increments up to 70 cm in depth. Access tubes are installed in the sod plots and near the blue mist spirea, common lilac, serviceberry, smooth hydrangea, and three leaf sumac shrubs. The Redosier dogwood shrubs will have diviner tubes installed spring of 2009 so that soil moisture data can be taken on that species, as well.
An infrared thermometer will be used to document stress in the grass species. These measurements will be taken at solar noon (11:30 AM – 12:30 PM). The ratio between grass temperature and ambient temperature will indicate the decreasing efficiency of the grass boundary layer as water becomes limiting.
Height and width measurements will be taken on regular intervals to determine plant vigor. Additionally, visual measurements, accompanied by pictures, will be taken at regular intervals to determine aesthetics.
Pot-in-pot Lysimeter Study:
The pot-in-pot lysimeter study is a randomized block design. The pot-in-pot system is used in the lysimeter study to gravimetrically determine the amount of water loss due to ET. A series of dry-down periods will be conducted throughout the growing season. A dry-down period is a period in which water application to a plant is limited. As a plant transpires, the soil becomes drier and water is less available to the plant. Dry-downs will be done in order to determine how plants react to a limited water supply.
Site of lysimeter study with equipment to lift plants.
There will be 3 treatments in the pot-in-pot experiment. Row 1 will receive 25% of the ET rate, row 2 will receive 50%, and row 3 will receive 100%. The outermost row of plants closest to the turf area will act as a barrier in an effort to reduce drift from the sprinklers that water the adjacent turf. There will be 5 repetitions of 2 different species in each row. The 2 species that were chosen for the pot-in-pot experiment were the smooth hydrangea and Redosier dogwood. As was with the drought tolerance study, a pressure chamber will be used for this study to determine the physiological differences in plant responses to drought stress. Height and width measurements, visual ratings, and pictures will also be taken for this portion of the experiment. Through taking some of the same data in both the drought tolerance study and the pot-in-pot lysimeter study, the data can be analyzed to determine if there is a relationship between both study types.
Results:
Even though treatments only started on 6/27/08, results are already starting to appear from the pressure chamber and the Diviner 2000. Results for the Diviner 2000 are what would be expected. The 100% treatment plot has more moisture in the soil at a deeper depth than the 0% treatment plot. The pressure chamber data shows that common lilac is more stressed in the 0% treatment plot and progressively less stressed in the 100% treatment plot. The three leaf sumac seems to show really no difference in water stress among all 4 treatments. The serviceberry is in between he three leaf sumac and the common lilac.
Thanks to: Colorado Agricultural Experiment Station; Colorado Nursery and Greenhouse Association; Colorado Nursery Research and Education Foundation; Garden Centers of Colorado; GreenCo Foundation; 2008 plants donated by Alameda Wholesale Nursery, Arbor Valley Nursery, Fort Collins Wholesale Nursery, and James Nursery.
