Sunshine Mimosa --A Native Groundcover We Can All Appreciate
E. Allen Stewart III P.E.----November 1, 2017
In my previous Blog (Try Going Native to Save Money, Do Good, Protect Posterity and Have Fun) I presented a review of the benefits and challenges associated with landscaping with native plants. In this follow-up Blog my intent is to extend this review into a specific native groundcover, which I, and others, believe has substantial potential both in residential and institutional applications in Florida, and other southern states. But this potential can be realized only with serious attention from agronomist, horticulturists, economist, growers, trade and advocacy organizations, landscape architects, civil engineers, ecologists, the interested and involved public, and of course, politicians. As always comments and rational arguments and criticism, are welcomed.
Sod farming and seed production is a big deal in Florida, with over 103,000 acres in cultivation. In a 2009 report by the University of Florida Institute of Food and Agricultural Sciences (IFAS) (1), the 2007 revenue associated with sod farming in Florida was reported at $703 million, which generated $22 million in taxes and supported 5,633 jobs. The predominant grass grown at these farms was St. Augustine (51%) followed by Bahia (35%). Floratam was by far the predominant cultivar of St. Augustine grass.
Sod of course is used to establish turf for residential lawns, commercial spaces, road banks and swales, easements and rights-of-way, parks, pond banks, sports fields, golf courses, and several public areas not mentioned. The mechanization of sod farming has made the collection, transport and installation of sod comparatively inexpensive, and allows a mature lawn to become established in a short time. However, as noted previously, this turf requires mowing, often needs irrigation and fertilization, and can be vulnerable to pests, poor soil conditions, disease and weather extremes. In addition, the sequestration of atmospheric carbon dioxide offered by turf grass is largely off-set by the fossil fuels required for maintenance.
In place of sodding, seeding of Bahia is commonly used by the Florida Department of Transportation (FDOT) to establish turf along major highways. Bahia seed is comparatively inexpensive, and under proper soil conditions the turf develops quickly. Once established the Bahia turf requires little attention other than periodic mowing. Presently, FDOT can obtain mowing services at relatively low costs, presumably because the extensive areas allow contractors to benefit from economy-of-scale, and because the price of fuel is presently low. Fuel costs however can be expected to increase eventually, and mowing costs will likely increase accordingly.
The question then, what is the nature and magnitude of a potential native groundcover which could avoid or reduce the disadvantages of a traditional turf grass? If there is, what would be the nature of its advantages and disadvantages, and what situations would be most applicable? I believe one potential candidate is a plant called sunshine mimosa—Mimosa strigillosa—often shortened to mimosa within this text.
As a kid growing up in Florida, I spent a lot of time outdoors exploring nature. When in open areas within flatwoods or along the fringes of wet savannahs I remember a little plant with pink powder puff flowers. We always liked to find these because if you touched the feathery leaves they folded up. My mother called them mimosa, which I thought was rather strange, as I thought of mimosa as a tree. But she was right, as usual.
Over the years, as the Native Plant Industry has grown in Florida, so has interest in the use of sunshine mimosa as a native groundcover. Sunshine mimosa offers several advantages, the most notable being:
It is attractive. Growing as a low groundcover, rarely reaching a height over 6”, it displays small pink powder puff blooms surrounded by a green “lawn” which adds color to an open vista. And these blooms attract pollinators—primarily honey bees.
The low profile of sunshine mimosa means that it does not need to be maintained through an intensive mowing regimen. Mowing is typically not necessary, although in residential applications occasional mowing (1-2 times per year) may be used to maintain a more cropped, shorter profile. Also, occasional mowing (maybe 1-4 times per year) may be needed if the area is invaded by weeds or grasses which can compete with the mimosa if allowed to become established vertically. In comparison, mowing of residential lawns is typically required 1-4 times each month.
Sunshine Mimosa as groundcover on sloped road shoulder.
Because of its deep roots and its tolerance of drought, irrigation water is not required to sustain an established lawn of sunshine mimosa.
The deep roots of sunshine mimosa not only enhance drought resistance, they also provide effective erosion control, especially during prolonged drought periods when turf grasses might lose their root structure and die. Erosion control is particularly important in public works where banks as steep as or steeper than a 4:1 horizontal to vertical ratio are unavoidable. Of course, the steeper an engineer can design the bank, the lower the earthwork costs, but greater the risk of erosion and the more difficult the access for maintenance equipment, such as mowers. Because sunshine mimosa needs little mowing, and likely provides more effective protection from deep erosional rutting, it may be ideally suited for these higher slopes. Not surprisingly, mimosa is attracting the attention of some Civil Engineers as well as Landscape Architects for such applications. The cost savings to be realized is not only with maintenance costs, but also potentially with construction costs—i.e. more opportunity for steeper slopes.
Sunshine mimosa is a legume, and thus “fixes” atmospheric nitrogen through a relationship with special microorganisms within their root zones. This means no nitrogen fertilization is required, and because their phosphorus demand is low, phosphorus fertilization typically is not required.
Sunshine mimosa has no known devastating diseases or pests, except for one infestation of a yet to be identified slime molds which impacted a cultivation unit in Central Florida (2). While certain native butterfly larvae (caterpillars) do use the plant, they are not seriously injurious.
So, with these advantages, what are the disadvantages, and what are the challenges which would be associated with acceptance and implementation? For residential and commercial applications in Florida there is a well-coordinated effort to promote this plant among IFAS Extension Offices, the trade organization Florida Association of Native Nurseries (FANN) and the advocacy groups Florida Native Plant Society (FNPS) and the Florida Wildflower Foundation, as well as the involved specialists and professionals within the private sector.
Stephen Brown, Horticultural Agent, and Kim Cooprider, Master Gardener, both working with the IFAS Lee County Extension, provided a 2010 summary of mimosa, including a review of methods for cultivation and maintenance. They reiterated the advantages already mentioned, but did note that mimosa does not compete well with weeds, and care is needed to minimize weed encroachment in areas targeted for mimosa coverage. They suggested that about 4 plants reasonably spaced could facilitate coverage of about 300 square feet in one growing season.
Ralph Mitchell, Director and Horticulture Agent for Charlotte County IFAS Extension, issued a similar summary of mimosa. Thomas Becker, also with the Charlotte County IFAS Extension serving as Training Specialist for the IFAS Florida Friendly Landscaping™ program promotes native landscaping and mimosa use among residential communities in Charlotte County, and has prepared an effective PowerPoint which he uses during presentations. He places emphasis upon the environmental benefits of the program, particularly as related to direct and indirect protection of the water quality within Charlotte Harbor.
Mr. Becker recently made a presentation to the community in which I live—Pirate Harbor in Punta Gorda. I was out of town when he made the presentation, but from what I have heard it was well received. There are a few houses in our community that have landscaped in native vegetation. A couple yards (including mine) are almost exclusively (circa 80%) in native plants. Sunshine mimosa is not commonly used in Pirate Harbor, with only two yards that I could see which have included it within the mix of native plants. Hopefully that will change following Mr. Becker’s presentation.
As I mentioned in my previous Blog, change usually comes slowly, and I am not certain people will attempt to replace their Floratam yards with mimosa without some type of help and motivation. Certainly, programs such as those promoted by IFAS are most helpful, but IFAS needs to be supported by private sector specialists and other local and state governmental officials who can provide incentives, services and expertise for those who do want to convert to mimosa. Such conversion can reduce maintenance (mowing) costs, which will be attractive to those who pay several hundred dollars a month for mowing services. But for those who mow their lawns themselves, and who find getting on a riding mower on the weekends as a therapeutic ritual, conversion to mimosa may offer less appeal. In Pirate Harbor, and similar communities, the residents also pay a considerable amount for mowing “common areas” such as easements and “islands”. This could be where mimosa could save money for all the homeowners, and perhaps serve to start a trend.
The use of mimosa in residential areas most likely will gain popularity with time. With native plant nurseries, landscape designers and maintenance specialist becoming more prevalent, and with the trade organizations and advocacy groups becoming ever more influential we should see more yards in mimosa throughout much of Florida in the near future. Incentives from local, state and even federal entities of course would be helpful. These incentives could be as property tax reductions, lowered utility bills, or nutrient reduction or trading credits which might be associated with the Total Maximum Daily Load (TMDL) (3) requirements, or as might be included in Comprehensive Plans or Development Codes. Next year this time I will report through a Blog regarding progress made in the Pirate Harbor community.
To learn more about the potential institutional use of mimosa, I contacted Dr. Jeff Norcini. Dr. Norcini has a PhD in horticulture, and served for over twenty years with the University of Florida/IFAS, leaving in 2009 as an associate professor to start a consulting business—OecoHort, LLC. His primary interest has been in native herbaceous species, and he has been instrumental in helping to develop and implement the FDOT Wildflower Program. He presently serves as FDOT’s State Wildflower Specialist.
I asked Dr. Norcini about the possibility of establishing mimosa as a standard for FDOT rights-of-way. He was very supportive of mimosa as part of the wildflower program, but noted that because of the low cost of Bahia seed, it was unlikely that mimosa would replace it any time soon as a standard for expansive rights-of-way—if ever. He also said that if mimosa was to be used on such a large scale, seed production efforts would have to increase, as seeding would be the least expensive method of establishing large areas in mimosa turfs. Mimosa seeds must be scarified to ensure a high percentage of germination. Techniques for collecting and preparing seeds exist, but need to be optimized if a large mimosa seed market is to be developed.
There were two areas in which Dr. Norcini felt mimosa application by FDOT had the highest chance of large scale success. The first was the possibility of blending the mimosa seed with Bahia seed. Mimosa has been seen to coexist with Bahia in the field, and in situations in which soil pH is too high (>6.5) mimosa could become predominant, as Bahia does not do well in higher pH soils; Bahia performs best at pH 4.5 to 6.5, with the optimum being 5.5 (4). However, high pH soils, 7.6 to 7.9, are not uncommon along Florida roadsides (5). Those pH levels not only are well above the recommended pH for Bahia grass growth (4,6), but those conditions are detrimental to Bahia grass foliage and root growth (7) thereby making Bahia less competitive with weeds and other vegetation.
Because of the higher pH soils, particularly along roadbeds where calcium carbonate (lime rock) is common, it is possible that a mimosa/Bahia mix might require less mowing, and would enhance the aesthetic appeal of the roadside while providing some habitat value—particularly for bee pollinators. In poor soil conditions mimosa could serve as a viable substitute and help prevent erosion around bare areas abandoned by Bahia.
The other area in which mimosa could be of value would be along steep slopes, such as those seen at Interstate exits and overpasses. It is difficult and dangerous to mow steep sloped areas, so Bahia is not optimal. I have noticed native clump grasses, as well as palmetto and plumbago used on such slopes, but these may not provide the degree of erosion protection that would be offered by mimosa.
Dr. Norcini has had informal discussions related to these matters with colleagues. Obviously, what is needed is further field research followed by some test plot investigations. It would be difficult, and understandably so, to convince Highway Design Engineers to modify their standard specifications to include mimosa seeding for steep sloped areas. But if real advantages, in terms of maintenance cost, erosion control, and safety could be clearly demonstrated, then including mimosa in the construction documents could happen. This could stimulate the beginning of a seed production industry.
The people of Florida need to be thankful for the efforts of FDOT, the Florida Wildflower Foundation, Florida’s native wildflower seed industry, FNPS, FANN, IFAS and others. Hopefully their continued efforts will lead to widespread acceptance of mimosa and native landscaping throughout Florida.
It would be nice if some day when you are travelling along I-4 or I-75, or the Florida Turnpike, you could see a green and pink mimosa blanket covering sloped areas along the road, as well as colorful wildflower plots along the rights-of-way. Our posterity would also be appreciative.
Satterthwaite, L.N., A.W. Hodges, J.J. Haydu and J.L. Cisar. Feb 2009 An Agronomic and Economic Profile of Florida’s Sod Industry in 2007. University of Florida IFAS
Terry Zinn of Wildflowers of Florida, Inc. In Alachua, Florida experienced an infestation of a yet unidentified slime mold in one of his mimosa fields. The nature, virulence and identity of this slime mold has yet to be determined.
A Total Maximum Daily Load (TMDL) is a regulatory term in the U.S. Clean Water Act, describing a plan for restoring impaired waters that identifies the maximum amount of a pollutant (such as the nutrients nitrogen and phosphorus) that a body of water can receive while still meeting water quality standards.
Newman, Y., J. Vendramini, & A. Blount. 2010. Bahiagrass (Paspalum notatum): overview and management. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences. Retrieved October 26, 2017, from http://edis.ifas.ufl.edu/ag342
Sellars, B., & Ferrell, J. (2012, November). Undesirable Roadside Vegetation (Final Report: Research Contract #BDK75 977-54). Retrieved June 26, 2013, from Florida Department of Transportation Research Center: http://www.dot.state.fl.us/research-center/Completed_Proj/Summary_MNT/FDOT-BDK75-977-54-rpt.pdf
Silveira, M., Vendramini, J., & Rechcigl, J. E. (2012). Soil pH and liming issues affecting bahiagrass pasture. Gainesville, FL: University of Florida Institute of Food and Agricultural Sciences. Retrieved March 27, 2015, from http://edis.ifas.uf.edu/SS505
Rana, N., Sellars, B. A., Ferrell, J. A., MacDonald, G. E., Silveria, M. L., &
Vendramini, J. M. (2013). Impact of soil pH on bahiagrass competition with giant smutgrass (Sporobolus indicus var. pyramidalis). Weed Science, 61(1), 109-116. doi:10.1614/ws-d-12-00070.1