With plant breeders once again recognising its potential in the garden, lovely new varieties have been developed overseas, and at home some garden centres have started stocking a lovely new dwarf white form called Physostegia ‘Crystal Peak White’.
It’s an award winning dwarf form of the obedient plant which only grows about 40cm tall and remains nice and compact. Its tall, pure white flower spikes bloom for an extended flowering time from mid-summer to early autumn, making this variety an excellent addition to the front of mixed perennial beds and borders, and particularly delightful in containers.
The original form of Physostegia virginiana is a robust and easy to grow North American native perennial plant that belongs to the mint family, and grows almost anywhere - from Quebec to Florida to New Mexico! It is commonly called the “Obedient Plant” because each individual flower can be moved and arranged in different positions and will stay where you put them. It's a fun little trick to show people, and children are fascinated by this! Another common name is “False Dragonhead”.
The plants are upright, growing around 90cm tall when in bloom, and are clothed in lance-shaped, finely toothed leaves. The leaves and flowers are arranged on distinctly square stems, and it spreads by rhizomes to form an attractive and colourful plant in the garden. In summer, but especially in late summer and autumn, upright spikes of very pretty, snapdragon-like two-lipped flowers appear, attracting butterflies and other beneficial pollinators to the garden. Early garden varieties of the obedient plant come in lovely pastel shades of rose, lilac, lavender, pink or white.
In the Garden:
The obedient plant remains a popular perennial in many countries around the world, and is valued for its late season blooms at a time when the garden may not look at its best. It is beautiful in pots and valuable for adding contrast to the perennial border. Like mint, it loves moist soil, and will tolerate wet conditions beside a water feature, stream or pond.
Garden cultivars, like the newer dwarf varieties, are better behaved than the original forms of the obedient plant, which, unlike their common name, can become aggressive in the garden if they like where they are growing. Nevertheless, even when planting the newer types, bear in mind that they do spread quite quickly, so give them lots of room to grow - maybe in a naturalistic setting like a cottage garden or wildflower border.
The flowers attract many pollinators, and are excellent for cutting, lasting well in the vase.
Physostegia virginiana, Salt Lake City, Utah. Picture courtesy Andrey Zharkikh from flickrCultivation/Propagation:
The obedient plant grows well throughout most of the country, but is not well suited to humid regions, and in dry summer regions it will require regular watering in summer. It is a hardy plant which can tolerate some frost, enabling it to bloom into autumn, but as soon as the winter temperatures plummet, it becomes totally dormant until spring. In severely cold regions, mulch the soil in autumn to protect the rhizomes from freezing.
The obedient plant prefers full sun but can tolerate partial shade, particularly if it’s grown in a hot region. To flower really well it needs a minimum of 6 hours sunlight a day. To look at its best in the summer garden this perennial needs to be watered regularly, and especially during long, hot and dry spells.
Although in its native range the obedient plant can be found growing in woodlands and prairies with moist, well-draining soil, it is considered a bog plant, and if grown in these conditions, it prefers soils that are slightly acidic, typically ranging from 5.5 to 6.5.
In normal garden beds the best soil pH is acid to slightly alkaline (pH 5.5 to 7.5), and the plant will adapt to chalky, sandy, loamy, and even heavy clay soils if they are amended with compost.
Because the obedient plant thrives in fertile soil that holds moisture well, it may become aggressive in overly rich soil. To control its spread plant it on a drier, less fertile site and avoid using fertilisers. On sandy or impoverished soils, applying a complete fertiliser each spring together with a mulch of compost around the roots should suffice to keep the plant healthy and blooming.
Prune it right down in autumn and divide the plants every 3 years or so, if necessary.
Problems, Pests & Diseases:
Physostegia virginiana has minor issues with rust, spider mites, and aphids.
Warning:
Physostegia virginiana is not considered toxic to humans or animals.
Although it is often grown near water, pond fish are unlikely to eat it due to the oil-rich idioblasts that exist on its leaves and in its stems and roots. These produce a flavour that is evidently unpalatable, as evidenced by wildlife and insects tending to avoid this plant.