For many years, persicarias—also known as knotweeds—inhabited the periphery for me. I saw them but mostly looked past them, thinking of them as filler more than thriller. My first genuine appreciation came nearly 20 years ago after spotting a commanding swath of crimson-spired ‘Firetail’ nestled in a sea of palm sedge (Carex muskingumensis, Zones 4–9) in a new display garden at the Chicago Botanic Garden. Stylized meadows of this sort, championed by the landscape architects at Oehme van Sweden, are the perfect showcase for bold yet uncomplicated perennials like persicaria. With my interest piqued and eyes now wide open, my persicaria sightings became more frequent and satisfying. A trial to get to know them better was on my mind for years, but it took one notorious persicaria to finally make it happen.
Reasonable concern over the potential rambunctious nature of persicarias is justifiable, but a movement to banish all persicarias from our gardens was worrisome. Yes, the garden value of persicarias stacked against their potential invasiveness is a “knotty” subject. A closer look, though, shows that they’re not all thuggish; in fact, there are many garden-worthy persicarias.
[ TRIAL PARAMETERS ]
The Chicago Botanic Garden is evaluating 30 different persicarias in ongoing comparative trials. In 2011, a previous trial ran afoul of an errant bulldozer during garden renovations, so we started over again in 2012. Participants mainly included selections of Persicaria spp. and Fallopia japonica; numerous nomenclatural changes over the years have complicated the classification of these two groups.
Duration: 7 years
Conditions: Full sun; well-drained, alkaline, clay-loam soil
Care: We provided minimal care, allowing the plants to thrive or fail under natural conditions. Besides observing their ornamental traits, we monitored the plants to see how well they grew and adapted to environmental and soil conditions while keeping a close eye on any disease or pest problems and assessing plant injury or losses over winter.
See trial results by clicking here or the image below –
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