Matt Ounsworth and Dr. James E. Klett
Research on Landscape Shrubs and Turfgrass was conducted throughout the 2006 growing speason. The eight shrub species are Acer ginnala (Amur Maple), Amalanchier alnifolia (Serviceberry), Caryopteris x clandonensis (‘Dark Knight’ Blue Mist Spirea), Chamaebatiria millefolium (Fernbush), Perovskia atriplicifolia (Russian Sage), Rhus Trilobata (Three Leaf Sumac), Syringa vulgaris (Common Lilac) and Syringa meyeri (Dwarf Korean Lilac). The two turf grass species are Poe pratensis (Kentucky Bluegrass) and Festuca sp. (Tall Fescue). The research site is divided into two experiment areas the drought tolerance study and the lysimeter study. The drought tolerance study is a field study. All ten species of plants are subjected to four irrigation treatments. (0, 25, 50 and 100% of bluegrass evapotranspiration (ETo)) The lysimeter study uses a gravimetric lysimeter to obtain actual plant evapotranspiration.
Panoramic view of research site.
The four irrigation treatments in the drought tolerance study were started on May 22, 2006. Despite the record breaking heat, getting the heavy clay soil to dry down in the plots has taken some time. The Kentucky Bluegrass went dormant in early June in the 0% irrigation treatment. In the 25% irrigation treatment the grass started to go dormant in early July. By the end of August the Kentucky Bluegrass was completely dormant.
Tall Fescue did not perform well under the 0% irrigation treatment. However, Tall Fescue showed little stress in the 25, 50 or 100% ETo irrigation treatments.
Closeup view of irrigation system for turf plots.
There are no visual signs of stress in any of the shrubs under all irrigation treatments. Although. predawn water potentials indicate that the Common Lilac and Bluemist Spirea are developing a water deficit.
In the lysimeter study, shrubs were compared to reference evapotranspiration (ETo). It was found that Kentucky bluegrass estimated evaporation (ETo) overestimates Kentucky bluegrass’s actual evapotranspiration.
Four shrub species were looked at closely in the lysimter study. Those shrub species are Acer ginnala (Amur Maple), Rhus Trilobata (Three Leaf Sumac), Syringa vulgaris (Common Lilac) and Caryopteris x clandonensis (‘Dark Knight’ Blue Mist Spirea). The Amur Maple was thrown out of the experiment because it became chlorotic due to the soil’s high pH. Of the remaining species, the Three Lead Sumac used the least amount of water. While the Common Lilac and Spirea used higher but similar amounts of water.
Site of lysimeter study with equipment to lift plants.
The lysimeter has been useful in determing stress levels of plants. From this work we are able to predict when a shrub will wilt from stress. Our preliminary results indicate that plant rooting systems especially shrub rooting system versus grass rooting systems are a major limitor to plant drought tolerance.
Selected shrubs and turf were planted in plots receiving different levels of irrigation.
Fernbush (Chamaebatiaria millefolium) was one of the shrubs selected for the study.
Thanks to: Colorado Nursery Research and Education Foundation (CNREF) and Colorado Agricultural Experiment Station (AES) for partial financial support for this project. Partial in-kind donations of plant material are also appreciated form Fort Collins Wholesale Nursery and Bailey Nurseries Inc..
