A plant with a public image issue, Persicaria amplexicaulis ‘Alba’ (knotweed ‘Alba’). You may be familiar with this Polygonaceae by its older botanical name, Polygonum amplexicaule ‘Alba’. Polygonums, often called knotweeds, have a reputation as aggressive and weedy exotic, even invasive, plants. Persicaria amplexicaulis ‘Alba’ is a well-behaved garden plant with no aggressive or invasive tendencies.
Knotweed ‘Alba’, also known as mountain fleece ‘Alba’, is native to China, the Himalyas, and Pakistan where it is often found along stream-sides and wet meadows. In the garden setting, P. amplexicaulis grows best in USDA Zones 4-7 where it often reaches to 1.2 m (4 ft.) tall with a 1.2 m (4 ft.) spread. Plants will grow in full-sun to part-shade; however, if grown in full-sun plants must be watered often to prevent yellowing of leaves. When grown in part-shade with ample soil moisture, plants remain strongly upright and will form large, dense bushy colonies.
Persicaria amplexicaulis ‘Alba’ flowers from June-October/November producing terminal spikes densely packed with small, soft white flowers. The upright stems present ovate, stem clasping leaves with a matte green color. Since plants often form dense colonies, best to consider using P. amplexicaulis ‘Alba’ as a mass planting or in a large sweep in the garden. At Lurie Garden, ‘Alba’ is planted in combination with P. amplexicaulis ‘Firedance’ which provides great contrast in flower color.
|Botanical Name||Persicaria amplexicaulis ‘Alba’|
|Common Name||knotweed ‘Alba’|
|USDA Zone||4 thru 7|
|Light Requirement||Full Sun to Part Shade|
|Season(s) of interest||summer, fall|
|Height and Spread||1.5-3 ft x 1.5-3ft (45-90cm x 45-90cm)|
|Attracts Wildlife||Attracts Pollinators,|
|Additional Information||Not Native to the US Midwest. P. amplexicaulis native to the Himalayas.|
|Location in Lurie Garden||Southeast Dark Plate|