Edgewood College 
Rain Gardens

Printable Version

Abstract
Background
Methods
Results
Discussion
References

Abstract
This report deals with the health of plant life in Edgewood College rain gardens #1 and #3, the determination of which plants are best suited to the environment, and what could be done to maximize their health and survival. A sample of plant species was surveyed in each garden and each species' members counted. This data was compared with the population initially planted. Individual plant characteristics were researched to help hypothesize cause-and-effect of observed plant performances and to suggest future studies and experiments. More research is necessary, but new values have now been added to past data and a tentative list of plants most well suited to survival in Edgewood College's rain gardens has been produced based on this information.

Background
This study investigated the plant health in Edgewood College rain gardens #1 and #3, determined which species are best suited to these environments, and suggested what can be done to maximize their future health and survival.

Analysis of the rain gardens plants’ health was done through observation and research. Data was collected on a total of 22 different flower and grass species from the two gardens, which was then compared to the number originally planted.

This survey was a necessary first step in what could easily be a continuous process of surveying and experimenting. The eventual goal is to gain a real understanding of the health of Edgewood College’s rain gardens and determine the courses of action necessary to increase and preserve that health. Maintaining a healthy plant population will ensure the rain gardens’ continued benefit to the Lake Wingra watershed.

Methods
Our surveys of rain garden #1 were conducted in three sampling periods between October and November 2003. After studying already existent data, including a list of planted species and flowering data from June 2002 through August 2003, species were systematically chosen for inventory.

Two separate trips were made to rain garden #3 in December 2003. The original planting list was found for this garden, which allowed us to compare present plant numbers with the quantity originally planted. Identification was more difficult in this garden because nearly all of the plants were dormant and had wind damage. Samples of unknown plants were collected for later identification. With the help of various grass and wild flower field guides we examined the height, leaf shape, leaf pattern, seed structure, and flower structure of the samples and were able to confidently identify most plants.

After doing the actual fieldwork, we chose six species that seemed to be flourishing and six that seemed to be having problems and did in-depth research to form hypotheses as to how their differing conditions could have come about. Characteristics were selected based on environment, growing conditions, and other traits that could have been a factor in their observed numbers. The results of that study are below in tables 3 and 4.

Results

Data for tables 1-4 collected from the following sources:
Courtenay & Zimmerman, 1972; Ladd, 1995; Missouri Botanical Garden, 2004; Niering & Olmstead, 1979; Rook, 2002; USDA, NRCS, 2004; Wisconsin State Herbarium, 2004

Discussion
The purpose of this study was to take a closer look at the plants in the rain garden and analyze their status through observation and research. Specifically, we attempted to identify and count as many species of plants from the two gardens as possible, eventually taking data on 22 different flower and grass species. The second step of our analysis required us to learn more about the plants themselves and hypothesize what may have caused each plant to do as well or poorly as perceived.

We were able to categorize some of the important factors that may have led to the perceived flourishing of some rain garden plants and scarcity of others. The impact of these various factors on specific species should be determined experimentally to determine whether they were, indeed, involved in causing the observed conditions. Since this project only surveyed the garden, no real cause-and-effect relationships can be established. Therefore, the hypotheses we have proposed for the observed rain garden phenomena are merely hypotheses to be used as bases for future research.

The next step would be to do further observation of rain garden characteristics and gather experimental data. If, for example, one wanted to know if the amount of sun is a factor in the survival of a particular species, a schedule could be devised where the garden's sun exposure is recorded multiple times throughout the day, continuing from spring through fall. This data would provide the experimenter with how much sun each plant receives per day. Comparing this with the plant's sunlight needs and current rain garden performance would allow a conclusion to be made as to whether the amount of sun exposure has had an effect on the health of that species.

The hypotheses we have formulated cover a wide range of natural conditions, both stable and variable, external and internal, that may have had an impact on our observed data.

As mentioned, one of the stable conditions that may have affected the success of the rain garden species is sun exposure. Rain garden #1 is half shade, half sun. Almost all of the plants that we singled out as having the most trouble were full sun plants. Again, a follow-up study could monitor the sun exposure of the rain gardens and see if the problems these plants are having could be caused in part by not getting their optimum sun requirements.

Another likely factor affecting plant performance is soil type. The soil in both rain gardens is mostly clay, which is notoriously difficult to grow plants in because it is heavy and fine, causing roots to have trouble penetrating it, drainage to be slow, and spring warming to be later than normal (Wilderness Nursery, n.d.). Although most of the faltering plants in our sample were said to grow in sand, loam, and clay, they most likely prefer loam and although they survive in clay, they probably have trouble flourishing in it.

We also believe that drought tolerance played a role in the observed numbers of some plants. Beginning in late June 2003 and lasting well into September, Wisconsin experienced abnormal dryness that led to severe drought conditions (Drought Monitor Archive, n.d.). This drought ravaged many of Wisconsin's crops and plants, and some of Edgewood's rain garden plants need constant moisture, making them especially vulnerable to droughts. According to one botanical website, plants like boneset (Eupatorium perfoliatum) frequently experience scorched leaves as a result of extreme drought (Missouri Botanical Garden, n.d.). Ironically, boneset is one plant we noticed was doing particularly well in the rain gardens, indicating that although this factor may have played a role, it was not a major factor in plant health. Admittedly, since the plants were dormant by the time we surveyed the rain garden, some boneset plants may very well have died during the fall and were assumed dormant. This concern could be easily resolved by resurveying the garden in the spring.

Similar to the drought hypothesis, we believe that the varying rainfall patterns of the past year served to harm a wide range of rain garden species. We noticed after looking at the National Weather Service website that the heavy at times, nonexistent at others rainfall patterns may have alternately shocked the drought-tolerant plants with a deluge of rain and the water-needing plants with drought and oppressive heat.

It is also thought that the lack of mulching and supplemental watering during last summer's drought may have led some of the less drought tolerant plants, like prairie cord grass (Spartina pectinata) and ironweed (Vernonia fasciculate), to dry out and fail to recover (Stromme, 2001).

We also feel it important to note that at the time of our data collection the rain gardens were only 3 and 1½ years old, respectively. This fact may account for the lack of spreading of some species. Some plants, such as big bluestem (Andropogon gerardii), take a while to settle into an area, but maintain a solid presence once they have gotten established (Missouri Botanical Garden, n.d.).

We also hypothesized that since some of Edgewood College's rain garden plants seemed to perform too well, they may have crowded out nearby vegetation. At the time of our survey the rain garden had not been "weeded" in a while, and some of the invasively spreading plants were visibly overtaking the smaller ones. Therefore, one could reasonably suggest that those "weedy" plants may have overtaken the smaller, less aggressive species and either choked them out or buried them under their own growth. If this was, indeed, a factor, which could be determined by follow-up research, it could be easily controlled by regular rain garden maintenance.

Similarly, several of the plant species determined to be in good health are generally considered somewhat weedy and able to bounce back after disturbances. Those plants include the various sedge species (Carex spp.), New England aster (Aster novai-angliae), cattail (Typha), and sweet Indian plantain (Cacalia suaveolens). Therefore, the aggressive characteristics of some plant species may have allowed them to better survive and bounce back after the drought, implying that they would be more likely to survive and even flourish than the other species during the less extreme weather fluctuations common to Wisconsin summers.

Some of our observations are difficult to explain. The Typha, or cattail, was by far the most numerous among all of the rain garden plants surveyed. It does extremely well in moist, marshy areas, which would explain its success in the rain garden, but made us wonder how the cattails survived the drought so well. We thought the answer might lie in the cattail's root system: the underground rhizomes allow it to flourish even if the exposed plant is destroyed (Rook, 2002). We couldn't find any information, though, that directly linked these rhizomes to the plant's ability to survive droughts. This phenomenon would require further research and a separate experimental study to completely understand.

We also observed in our sample population that the faltering plants required full sun and half of them were purported to thrive in dry climates. Surprisingly, few of the flourishing plants were said to tolerate dry conditions (a notable exception being Elymus villosis, silky wild rye). This is very strange considering "common sense" would indicate that plants that can tolerate both extremely wet and extremely dry conditions would be ideal for a Wisconsin rain garden. Again, only further study and a controlled experiment can shed light on this matter.

We began this study with the intention of selecting several rain garden plants that seemed best suited to the Edgewood College rain garden environment to plant in a new garden. Based on our data, we believe that the most hardy plants and therefore most likely to survive and flourish in the garden would be the New England aster (Aster novai-angliae), sweet Indian plantain (Cacalia suaveolens), various sedge species (Carex spp.), silky wild rye (Elymus villosis), boneset (Eupatorium perfoliatum), and cattail (Typha). Although we are reasonably confident that these species have been the most successful of the community, the nature of this survey is such that we cannot be certain that this data has external validity; that is, we cannot be sure that this data can be generalized to a different rain garden and a different time. The conditions may be such that most of these plants die within months of being planted in the new garden. The reasons for the success of these species in rain gardens #1 and #3 are so varied that we cannot say with confidence that they are generalizable.

References
Courtenay, Booth, & Zimmerman, James Hall (1972). Wildflowers and Weeds. New
    York: Van Nostrand Reinhold Company.
Drought Monitor Archive. U.S. Drought Monitor. Retrieved February 19, 2004, from
    http://www.drought.unl.edu/dm/archive.html.
Ladd, Doug (1995). Tallgrass Prairie Wildflowers. Guilford, CT: Globe Pequot Press.
Missouri Botanical Garden. Kemper Center for Home Gardening. Retrieved February 19,
    2004, from http://ridgwaydb.mobot.org/kemperweb/plantfinder/Alpha.asp.
National Weather Service. Wisconsin Weather Extremes: 2003. Retrieved February
    19, 2004, from http://www.crh.noaa.gov/mkx/climate/2003arch/2003highlights.htm. Niering, William A. and Olmstead, Nancy C. (1979). The Audubon Society Field Guide to
    North American Wildflowers. New York: Alfred A. Knopf, Inc.
Rook, Earl J. S. (2002). Narrow Leaf Cattail. Retrieved February 19, 2004, from
    http://www.rook.org/earl/bwca/nature/aquatics/typhaan.html.
Stromme, Lorrie (2001, May 1). Plotting to Infiltrate? Try Rain Gardens. Yard & Garden
    News. Retrieved February 19, 2004 from
    http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-May0101.html.
USDA, NRCS (2004). The PLANTS Database. Retrieved February 18, 2004, from
    http://plants.usda.gov.
Wilderness Nursery. Soil Problems and Remedies. Retrieved March 23, 2004, from
    http://www.wildernessnursery.com/0203soilproblems.htm.
Wisconsin State Herbarium. Vascular Plant Species Database. Retrieved February 19,
    2004, from http://www.botany.wisc.edu/herbarium.