Several goldenrod species have been lumped together and called Canada goldenrod. This species complex has been divided into Tall goldenrod (Solidago altissimum) and Canada goldenrod (Solidago canadensis) and several variants of each (Nowick 2015, Megenhardt 2015, Semple et al. 2015, Melville and Morton 1982). While I thought I was dealing with Canada goldenrod, the common and aggressive one is Tall goldenrod. See the Resources section for ID notes.
Tall goldenrod can quickly establish a monoculture in the early stages of restoration or whenever there is plenty of open space and little competition. It spreads by seeds and by rhizomes and it effectively creates its own space by shading neighboring plants (Eiltes et al. 2011). Our goal is to mitigate it, not eliminate it because at least 54 of our native insects need this plant, providing immense ecosystem value and biodiversity (Hess 2020).
We’ve had some success managing this bully plant but it hasn’t been wildly successful. Clone-forming plants, such as Tall goldenrod, spread by producing vegetative offspring via rhizomes that remain connected to the original plant. I realized I needed a deep dive into the plant’s biology and the scientific literature to guide our efforts. The techniques created were done so under trial and error and paying attention to the outcome. Why these techniques work is explained by science.
Goldenrod Growth and Development
Tall goldenrod is a good invader of early successional habitats (e.g. new restorations or plantings) and after disturbances. Typically one finds it establishes by seed in the 3rd, 4th, or 5th year of restoration and after that spreads rapidly via rhizomes (Hartlett and Bazzaz 1983, 1985).
Tall goldenrod rosettes break dormancy between late March and mid-April. Climate change could alter this timing but this generally guides the rosette schedule. Within weeks of the rosette appearing, shoots (i.e. stems and leaves) begin developing and the growth rate is at its highest and carbohydrates and other nutrients are moving from the roots and rhizomes to the leaves (Bradbury 1981, Abrahamson and McCrea 1985). By late May, underground carbohydrate storage is at the season’s lowest (Bradbury 1981).
Tall goldenrod steadily increases its conversion of light to nutrients (photosynthetic actions) after blooming (generally Sept and Oct) with all nutrients directed toward rhizome growth (Werner et al. 1980, Bradbury 1981, Bradbury and Hofstra 1977). Rhizome buds continue elongating and new growth is highest for a month or so after we physically see the bloom and the seed set (Hartnett and Bazzaz, 1983). Removing the stem and leaves (i.e. the shoot) late in the season before these rhizomes stop growing doesn’t harm them. They will develop an aboveground green rosette which will overwinter and green up the following spring. (Werner et al 1980).
Flowers may not be produced until the 2nd year yet the rhizomes are actively generating new plants (Harnett and Bazzaz 1983). These plants are feeding roots and rhizomes that can store nutrients for 2-3 years (Werner et al. 1980, Bradbury and Hofstra 1977). The older plants spend more energy on bolstering rhizomes and clonal expansion than producing seeds (Werner and Platt 1976).
Soil moisture plays a role in Tall goldenrod seed development and dispersal. Plants in dry soil focus on vegetative expansion while plants in wet soil focus on seed distribution, thereby producing lighter seeds for further dispersal (Werner and Platt 1976, Abrahamsom and Gadgil 1973).
There’s much in the literature about goldenrod’s allelopathic abilities so I feel it should be addressed. Allelopathy is when one plant releases chemicals that inhibit the growth of another. In non-native regions such as Europe and Asia, Canada goldenrod is a problematic invasive plant but this doesn’t translate to its native regions. While it has these defensive chemicals, they aren’t “strong enough to alter community structure and turnover” (Pisula and Meiners 2010). It could be there was enough plant diversity to include “susceptible and resistant species” or “allelochemicals may have been metabolized by soil organisms so rapidly that their concentration in the soil decreased” (Pisula and Meiners 2010). This emphasizes the need for plant diversity.
Overseeding
Overseeding is a must for mitigating Tall goldenrod populations. In restorations, the competitive ability of other plants is crucial (Werner and Platt 1976). Tall goldenrod’s vegetative spread and seed production increases with disturbance and decreases with community species richness (Emery & Gross 2006, Abrahamsom and Gadgil 1973).
The optimal seed mix has yet to be tested because there are few studies of how surrounding plants are affected by clonal ones (Hartnett & Bazzazz 1985).
Through observations of several restoration practitioners, a partial plant list has been compiled. The plants in this list have been found growing within or tightly to the outside of clones. They seem to successfully compete with goldenrod, and thus may be good ones to use for overseeding.
Goldenrod Management Techniques and Timing
Mitigating Tall goldenrod will need a multi-pronged, multi-year approach. Management techniques differ based on the size and density of your infestation. We’ve had success in small areas using the lop and treat method and swiping with herbicide (This can be done in conjunction with brushcutting or not.). Mowing to prevent seed set in larger areas has reduced the number of plants. Since soil moisture plays an important role in the spread of seeds, we prioritize management in the wet mesic areas. Whether it’s a large or small area, overseeding is important.
If the area is blanketed with Canada goldenrod and few or no native plants, mowing could reduce the clones but would not kill them. Once the clones are reduced, mowing this consistently could damage desired plants.
Tall goldenrod (Solidago altissimum) mowed annually for 6 years during the peak blooming time depleted rhizome resources and decreased clonal growth but did not completely remove it (Stoll et al. 1998, Meyer & Schmid 1999). Neither of these studies were concerned with replacing the Tall goldenrod with native plants so neither addresses this. In practice, one would overseed and encourage desired plants.
I created this table of management techniques and timing for easy reference.
| Season | Plant form | Treatment Options |
|---|---|---|
| March-April | Rosette | Option 1: Spot herbicide rosettes once greened up. I use a 2% mix of aqueous trichlopyr (4 oz to 1 gal) |
| Mid-late May | 8-12” tall plant | Option 1: Mow (could burn but expect collateral damage to other biota Option 2: Spot herbicide |
| June – Aug | Growing | Spot herbicide |
| Late Aug-Oct | Blooming | Option 1: Mow then swipe herbicide on stems Option 2: Lop and treat Option 3: Brushcut, remove debris, swipe herbicide on stems Option 4: Mow |
| Nov – Jan | Senesced | Overseed treated areas |
Photos of positive progress
The following photos show positive outcomes for our mitigation efforts. In 2020 we mowed quite a bit as shown by the wider mowing paths that covered a larger area. In 2021, we found more desired plants filling in and reducing the Tall goldenrod. These photos demonstrate our positive gains mitigating goldenrod using these techniques.
Tall goldenrod is a tricky plant to mitigate. Dormant season burns and mowing encourages its growth. Herbiciding techniques miss plants and since Tall goldenrod has long term root and rhizome storage capabilities, it requires various techniques over several years to see results.
This example management plan shows how the combination of techniques and timing can be mixed and matched. Because we’re working with nature, this is merely a guide. I have begun this management in late August. That has been the timing of my initial treatment but you’ll see in subsequent years, management is considered as early as March.
Conclusion
Tall goldenrod is a native and has value to our native insects. Since we manage for diversity, this makes mitigation our goal, not eradication. Based on the biology of Tall goldenrod, managing it to reduce its invasions requires various techniques used throughout the year for several years.
Because each piece of land is unique, and management is driven by size, density, soil moisture, and landowner resources, the combination of management techniques could differ. This is the beauty of having a toolbox filled with options. Mixing and matching techniques and timing based on the plant’s biology increases the probability of a favorable outcome.
Resources
Practically speaking, Canada golden and Tall goldenrod are the same in an ecosystem but knowing the difference and being able to refer to the plant properly is important to me. Here’s some links and tips that will help you.
Full descriptions of Solidago canadensis and S. altissiumum
There are 2 main differences to look for: the leaf underside and the pappus hair length
Leaf undersides:
S. canadensis leaf undersides are hairy on veins only
S. altissimum leaf undersides are hairy on the surface and veins
Pappus hair length:
S. canadensis pappus hairs are less than 2.3mm long
S. altissimum pappus hairs are more than 2.4mm long
References
Abrahamson, W. G., & McCrea, K. D. (1985). Seasonal nutrient dynamics of Solidago altissima (Compositae). Bulletin of the Torrey Botanical Club, 414-420.
Abrahamson, W. G., & Gadgil, M. (1973). Growth form and reproductive effort in goldenrods (Solidago, Compositae). The American Naturalist, 107(957), 651-661.
Bradbury, I.K. (1981) Dynamics, structure and performance of shoot populations of the rhizomatous herb Solidago canadensis L. in abandoned pastures. Oecologia 48, 271–276. https://doi.org/10.1007/BF00347976
Bradbury, I. K., & Hofstra, G. (1977). Assimilate distribution patterns and carbohydrate concentration changes in organs of Solidago canadensis during an annual developmental cycle. Canadian Journal of Botany, 55(9), 1121-1127.
Eilts, J. A., Mittelbach, G. G., Reynolds, H. L., & Gross, K. L. (2011). Resource heterogeneity, soil fertility, and species diversity: effects of clonal species on plant communities. The American Naturalist, 177(5), 574-588.
Emery, Sarah M. and Katherine L. Gross. (2006) Dominant Species Identity Regulates Invasibility of Old-Field Plant Communities. Oikos, Vol. 115, No. 3: 549-558.
Hartnett, D. C., & Bazzaz, F. A. (1983). Physiological integration among intraclonal ramets in Solidago canadensis. Ecology, 64(4), 779-788.
Hartnett, D., & Bazzaz, F. (1985). The Regulation of Leaf, Ramet and Genet Densities in Experimental Populations of the Rhizomatous Perennial Solidago Canadensis. Journal of Ecology, 73(2), 429-443. doi:10.2307/2260485
Hess, Marci. (2020). “Host plants and insects at Driftless Prairies.” Unpublished compilation.
Megenhardt, James David. (2015). “Allelopathic Effects of S. canadensis on the Germination of Native Prairie Plants.” Masters Theses. 2283. https://thekeep.eiu.edu/theses/2283
Melville, M. R., & Morton, J. K. (1982). A biosystematic study of the Solidago canadensis (Compositae) complex. I. The Ontario populations. Canadian Journal of Botany, 60(6), 976-997.
Meyer, A. H., & Schmid, B. (1999). Experimental demography of rhizome populations of establishing clones of Solidago altissima. Journal of Ecology, 87(1), 42-54.
Nowick, Elaine. (2015). “Historical Common Names of Great Plains Plants, with Scientific Names Index. Volume II: Scientific Names Index.” Zea E-Books. Book 28. http://digitalcommons.unl.edu/zeabook/28
Pisula, Nikki and Meiners, Scott J. (2010). Allelopathic Effects of Goldenrod Species on Turnover in Successional Communities. Faculty Research & Creative Activity, 27. http://thekeep.eiu.edu/bio_fac/27
Sachs T. (2002) Developmental processes and the evolution of plant clonality. In: Stuefer J.F., Erschbamer B., Huber H., Suzuki JI. (eds) Ecology and Evolutionary Biology of Clonal Plants. Springer, Dordrecht.
Semple, J.C., H. Rahman, H., S. Bzovski, M.K. Sorour, K. Kornobis, R. Lopez Laphitz, and L. Tong. 2015. A multivariate morphometric study of the Solidago altissima complex and S. canadensis (Asteraceae: Astereae). Phytoneuron 2014-10. 1–31. Published 12 February 2015. ISSN 2153 733X
Stoll, P., Egli, P., & Schmid, B. (1998). Plant foraging and rhizome growth patterns of Solidago altissima in response to mowing and fertilizer application. Journal of Ecology, 86(2), 341-354.
Tang, & Kuang, & Qiang, Sheng. (2013). Biological control of the invasive alien weed Solidago canadensis: combining an indigenous fungal isolate of Sclerotium rolfsii SC64 with mechanical control. Biocontrol Science and Technology. 23. 10.1080/09583157.2013.820255.
Werner, P.A., I.K. Bradbury, and R.S. Gross. 1980. The biology of Canadian weeds. Solidago canadensis L. Canadian Journal of Plant Science 60:1393-1409.
Werner, P., & Platt, W. (1976). Ecological Relationships of Co-Occurring Goldenrods (Solidago: Compositae). The American Naturalist, 110(976), 959-971. Retrieved August 31, 2021, from http://www.jstor.org/stable/2460024
