Physostegia: planting, cultivation, maintenance

Description and Botany

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The Physostegia or obedient plant is a herbaceous perennial from the Lamiaceae family, like mints. It grows spontaneously in sunny meadows and moist forests, along riverbanks and in marshy areas of North America, particularly in the state of Virginia, where it thrives abundantly.

The genus Physostegia comprises 12 species, but only Physostegia virginiana is cultivated in our gardens. It has given rise to many interesting cultivars.

From a rhizomatous stump, beautiful glabrous, erect, quadrangular stems rise, depending on the varieties and growing conditions, from 45 cm to 1.20 m in height in all directions. The plant forms a dense bushy clump with a spreading habit. Fast-growing and semi-suckering, it can spread vigorously, sometimes becoming invasive if conditions are suitable.

The unbranched stems are adorned with dark green, glossy leaves, arranged in whorls, that is, in opposite pairs all around the stem. They are deciduous, glabrous, lanceolate with finely dentate edges, and approximately 5 to 15 cm long. It is margined in white in Physostegia virginiana ‘Variegata’.

The spike inflorescence of tubular flowers, and a botanical plate from 1899 (F.A. Stokes)

In mid-summer, sometimes extending into early autumn, the pastel flowering spikes rise above the foliage, borne at the tips of the stems. From July to October, depending on the varieties, the obedient plant raises branched floral spikes of 10-12 cm in length, laden with small tubular flowers. These are densely and regularly grouped, arranged in 4 vertical ranks on the stem. They bloom from the bottom upwards. They take the form of flared tubes 1 to 3 cm long, composed of 5 lobes encased in a short calyx. The upper lip forms two lobes, and the lower lip, three lobes. The inside of the corolla tube reveals four stamens and one pistil. The flowers of Physostegia resemble those of foxgloves.

Although the wild form is purple-pink, the flowers can display other colours. Beautiful variations can be found in shades of pink, including light lavender pinks, fresh pinks, candy pinks, magenta purples, or sometimes pure white, like Physostegia virginiana ‘Summer Snow’, making the plant very elegant.

These narrow candles hide a botanical peculiarity: jointed by a small organ that acts as a hinge, the flowers temporarily change orientation when touched, which has earned the plant the nickname “obedient plant,” appearing as if struck by catalepsy.

The flowers of Physostegia, which hold well in a vase, make excellent cut flowers for bouquet arrangements.

It is a melliferous plant: its pollination occurs through insects, particularly bumblebees and bees. After flowering, the flowers produce numerous small black seeds.

The obedient plant is sometimes also referred to as “obedient plant” due to the fact that the flowers, once touched, do not return to their original position.

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Main varieties

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Physostegia virginiana Summer Snow - Obedient Plant

This variety features snowy spikes on beautiful light green foliage. This flowering physostegia creates a small event in the garden.

• Flowering time August to October
• Height at maturity 60 cm

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Physostegia virginiana Bouquet Rose - Obedient Plant

This is the most widely cultivated cultivar! Perfect for sunny beds in humid climates!

• Flowering time August to October
• Height at maturity 70 cm

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Physostegia virginiana Vivid - Obedient Plant

A vigorous perennial bearing beautiful candy-pink flower spikes all summer long. Very lovely at the edge of a water feature or for making cut flower arrangements.

• Flowering time September to November
• Height at maturity 60 cm

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Physostegia virginiana Variegata - Obedient Plant

This variety produces narrow, slightly stiff spikes covered in fresh pink flowers on very bright variegated foliage in summer. It will also find its place in perennial and bush beds.

• Flowering time August to October
• Height at maturity 60 cm

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Physostegia virginiana Red Beauty - Obedient Plant

This is undoubtedly one of the most richly coloured varieties of cataleptic. It will attract all eyes.

• Flowering time August, September
• Height at maturity 80 cm

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Physostegia virginiana Galadriel - Obedient Plant

A lovely dwarf variety that produces slender spikes laden with pale lavender flowers. It will accompany other plants in damp banks.

• Flowering time August, September
• Height at maturity 45 cm

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Physostegia virginiana Miss Manners - Obedient Plant

A compact, non-invasive, bright and floriferous variety. Stunning by water features, its flowers are also very beautiful and long-lasting in bouquets.

• Flowering time August to October
• Height at maturity 55 cm

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Planting Physostegia

Where to plant it?

Virginia physostegia is a very hardy plant, tolerating temperatures as low as -30 °C. It is an easy-to-cultivate perennial that thrives in moist soil, preferring cool conditions. It will do well in full sun or very light shade, in any good light garden soil that is cool to moist, even waterlogged in summer, but not too rich, and sheltered from strong winds. Indeed, as these are quite tall plants, strong winds could break the stems!

In overly rich soil or too shady an exposure, the stems tend to elongate and flop over. Full sun is ideal, especially if you live in northern France. It is perfect for sunny borders in humid climates.

This is a plant that takes up space, so ensure there is enough room around it, as it does not like competition from other roots and may tend to smother its neighbours.

The ideal soil is one that does not dry out in summer. Physostegia is perfect for dressing the edges of ponds, water features, or a marsh, where it will brighten the area with its luminous flowering alongside other moist bank plants. It will also thrive in well-watered borders in wild and naturalistic gardens that are kept cool.

Physostegia is a stunning ornamental plant by the pond or water feature

When to plant the physostegia?

Physostegia should be planted in spring around March-April once the risk of frost has passed, or in autumn, from September to November.

How to plant it?

This beautiful perennial needs a bit of space to develop properly, maintain at least 50 cm distance between plants, or even 1 m, as the plant can occupy 1 m² after 2 years of cultivation.

In overly sandy or stony soils, add some compost. Plant about 5 plants per m².

• Dig a hole 2 to 3 times wider than the root ball
• In poor soil, add some well-decomposed compost at the bottom of the hole
• Plant the root ball, bring the soil around it, and firm it down
• Water generously and then regularly in summer until the plant is established
• Keep the soil cool at the base with organic mulch during summer

When and how to sow Physostegia?

Sow Physostegia seeds from February to July. Germination is very slow.

1. In trays or pots, place the seeds on the surface of a seed compost.
2. Enclose everything in a plastic bag or a warm, bright place to maintain a temperature of 20 to 25 °C.
3. Keep the compost cool and moist but not waterlogged.
4. Transplant the young plants into 8 cm pots when they are sturdy enough to handle.
5. Keep them under a cold frame and plant them in the garden the following spring, spacing them 60 cm apart.

Maintenance and Care

If Physostegia has been planted in a suitable location (in cool soil, in the sun), it will require very little maintenance.

Physostegia needs soil that is always moist. Do not hesitate to water during dry spells. If planted by a water feature, there is no need to water. Mulch the soil in June with grass clippings or good organic mulch.

Regularly remove faded flowers at the base of the foliage to prolong flowering.

At the end of winter, cut back the clumps and dried stems to ground level. If your plant becomes invasive, limit the spread of the clump by dividing it (approximately every three years).

Cataleptics are hardy and robust plants that are not susceptible to diseases.

Physostegias before flowering, in mulched soil, and at the end of the season in autumn, a dry clump that should be cut back in early spring (Photos F.D. Richards)

Multiplication

Physostegia is preferably multiplied by division, which is easier and quicker than sowing. Moreover, division has the advantage of rejuvenating the clumps while producing new plants.

1. In spring, using a forked spade, dig up the clump, retaining as many rootstocks as possible
2. With the edge of a spade, divide the clump into several sections containing roots
3. Replant them immediately in a new location in well-tilled, fresh soil
4. Water generously

Associate

Physostegia is a perennial that thrives in rather moist soils, making it perfect for the edges of ponds where it forms lush, compact clumps. It is essential for brightening cool areas in all natural gardens. Its pastel pink, pure white, or candy pink inflorescences bring a sense of lightness near a pond, in a damp flowerbed, or in a cool border.

Its elegant silhouette will complement that of other perennials for wet banks, such as river anemone, Japanese iris, goat’s beard, meadowsweet, butterbur, and knotweeds.

At the edge of a waterfall, stream, pond, or basin, it will look wonderful alongside Eriophorum angustifolium or “narrow-leaved cotton grass” and a purple loosestrife.

Pair your Physostegias with naturally appearing plants like goat’s beard or purple loosestrife – companions for cool soils[/caption>

 

Its pink or white flowers will pair well with the mauve and other cool tones of the graceful Astilbes, and with the variegated foliage of Houttuynia cordata ‘Chameleon’, a small groundcover perennial.

It will quickly become indispensable in a pink garden or white garden. At the edge of a chic and cool border, plant it at the base of perennials like summer asters or Verbena hastata and shrubs like groundcover roses.

[caption id="attachment_83605" align="alignnone" width="1172"] Beautiful mass effect in borders on the left (photo Andrey Zharkikh), and Physostegias in shades of pink (photo F.D. Richards)