Obedient plant: care, growth habit & varieties

With their dense spikes of flowers, obedient plants are stunning harbingers of late summer. Discover all there is to know about this vigorous plant, including some of its wonderfully unique varieties.

In the summertime, obedient plants (Physostegia virginiana) stand tall in the garden, while their showy flower spikes attract both people and pollinators. But watch out as, left to its own devices, this fast-growing perennial can quickly take over your garden bed, so it is best to keep it under control. Read on to find out everything you need to know about obedient plants, including how to keep these vivacious plants contained to one area.

Obedient plant: properties and origin

Obedient plants (Physostegia virginiana), also known as false dragonheads, are the only cultivated species of the plant genus Physostegia, which belongs to the Lamiaceae family. These plants originated in the central and eastern regions of North America, where they grow in wetlands and riverside brush.

These perennial shrubs are extremely vigorous plants and are considered invasive. They have underground rhizomes which form numerous root runners. Upright shoots can grow from these runners, reaching a height of 100 to 120cm. The developing root clumps have a width of 60 to 90cm. Obedient plant stems have four edges from which dark green, lanceolate leaves with serrated or toothed margins sprout. Between July and August, Physostegia virginiana produces densely packed spikes of pink-red to violet or white, tubular flowers which grow terminally on the end of long false branches. The characteristic flower heads are quite remarkable, since they grow in a hinged manner around themselves. After flowering, obedient plants develop bulbous stems with small fruit nuts.

Obedient plant flowers are especially valued garden ornamentals due to their tall, broad structure, and late summer splendour. They are great for adding a bit of height to garden beds or for growing in planters on balconies and patios. They are also suitable as cut flowers. Thanks to the obedient plant’s wetland origins, it can even be used to decorate pond edges and damp garden corners.

Are obedient plants bee-friendly? Physostegia virginiana‘snumerous flowers provide a rich source of nectar and pollen for various pollinators. Butterflies, bees, and bumblebees can benefit from obedient flowers. However, since this perennial is not native to the UK, they are not the best plants for promoting native insect populations.

Obedient plant varieties

The obedient plantvarietiesare wide-ranging. All Physostegia virginiana flowers share common features, like leaf shape, bee-friendliness, site requirements and the typical spike-shaped flowers. But depending on the variety, they differ especially in their growth height or flower colour. Obedient plants come in white, pink, red and violet blossoms. Here are some of our favourite obedient plant varieties:

• Physostegia virginiana ‘Summer Snow’: this variety reaches 70 – 80cm high and 30 – 40cm wide and has snow-white and medium-sized flowers that stay in bloom for a long time. The leaves are mid-green with a matte surface texture. It is ideal for growing in garden beds, as a border plant, and for cut flowers. White obedient plant flowers also provide a great contrast when planted alongside other coloured flowers.

• Physostegia virginiana ‘Summerspire’: this variety is characterised by large, panicle-shaped flowers, varying in colour from white to magenta-pink. The leaves are a matte green colour. This perennial grows 70 – 80cm tall and 50 – 60cm wide. ‘Summerspire’ is a robust variety, perfect for gardening beginners. It can be grown in borders, beds, and perennial gardens. Producing luscious blooms, it also makes a gorgeous cut flower for vases.

• Physostegia virginiana ‘Rosea’: this obedient plant variety has large, slightly fragrant, soft pink flower heads with vibrant green leaves. It grows between 30 – 35cm tall and 60 – 80cm wide. The ‘Rosea’ variety is extremely bee-friendly and is particularly suitable as a border plant and various other outdoor settings.

• Physostegia virginiana ‘Crystal Peak White’: this variety boasts small, pure white flower tips that bloom from June to September. The dark green leaves are lanceolate and pointed, with serrated margins. The variety grows 30 – 40cm in height and width, with a particularly dense growth habit.

Planting obedient plants: where and how

Obedient plants thrive in containers, beds, borders, perennial gardens, and make great companion plants to grow alongside other perennials.

If growing obedient plants in your garden, opt for a wind-protected location in partial sun to direct sunlight. Keep in mind that with less light, the plant grows fewer flowers. As false dragonheads prefer damp areas, plant them in damp or fresh garden areas. Choose a sandy-loamy, well-drained soil that is not too rich in nutrients to prevent this plant from growing too vigorously and taking over the area. When planting in pots or beds, a structurally stable soil is ideal. Our Plantura Organic Flower Compost is not only well-structured, but also peat-free, which benefits the environment as it produces less CO₂ during production compared to conventional composts. It also has a well-balanced NPK ratio that is suitable for growing obedient plants. For even better drainage, we recommend mixing a bit of sand into the soil.

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Plant your obedient plants between spring and autumn. Due to their broad growth and formation of runners, keep a planting distance of 30cm in garden beds. This equates to a maximum of eight to eleven seedlings per m². Cover the soil around the base of the plant with a layer of mulch to reduce evaporation.

Tip: wider planting distances also prevent diseases like mildew from spreading.

If you want to grow obedient plants on your balcony, choose a pot at least 20cm in diameter that can hold at least 5 litres to allow your plants plenty of space. It is important to create a drainage layer of gravel, pumice or expanded clay at the base of the pot to allow excess water to drain away.

It is also possible to grow your own obedient plant from seed. Obedient plant seeds require temperatures below 5 °C in order to germinate. For this reason, you will need to sow obedient plant seeds in autumn. Using seed starting pots is a good idea as they allow the young plants to adapt to their site conditions. As the seed germinate at different rates and over a long period of time, keep the seeds consistently moist and cool. Do not expose the seeds to direct sunlight.

Tip: colourful plants like bergamot (Monarda spec.), Macedonian scabious (Knautia macedonica) and lavender (Lavandula spec.) go well near false dragonheads.

Do snails eat obedient plants? Despite the fact that obedient plants lack thorns or toxic substances, they are in fact not targeted by slugs or snails. So don’t worry, the leaves and flowers are safe from these critters.

Obedient plant care

Obedient plants are robust perennials that are considered to be quite low-maintenance. However, since Physostegia virginiana usually grows very tall, it is a good idea to stabilise the stems with a plant support stake to prevent them from bending or breaking.

Watering and fertilising

During hot summers, water obedient plants little but often to keep the shallow root system from drying out. In the event of a prolonged drought, take care to keep the substrate moist at all times. Reduce water during the winter months. It is also important to avoid excessive watering to prevent waterlogging and root rot.

To prevent false dragonhead plants from growing too rampantly, refrain from fertilising regularly. Adding a bit of compost once a year in spring provides obedient plants with enough nutrients to give them a boost at the start of the growing period.

Pruning

After the flowering period, cut the spikes back to the uppermost leaves. Removing wilted flowers not only has an aesthetic appeal, but it also spares the plant from putting too much energy into forming seeds. It thus prevents unwanted self-seeding and spreading, and allows your obedient plant to invest more energy into forming shoots.

In late autumn, cut the obedient plant back to the base of the stem. Remove any diseased parts to avoid diseases spreading and to promote growth in the coming spring.

By the way: obedient flowers are exceptionally beautiful and durable cut flowers that bloom from the top down. To get cut flowers for vases, it is better to cut off the spikes once the lower flowers begin to open.

Rejuvenating obedient plants: dividing Physostegia virginiana every third year encourages vitality, flowering, and development, but it is also a method of propagation. Proceed as follows:

• After autumn pruning, lift the rhizome and roots out of the soil with a garden fork
• Divide full rhizome into pieces, each with intact root systems
• Plant the young parts of the rhizome back in the original place
• Water rhizomes thoroughly
• Plant or dispose of the extra rhizome pieces elsewhere

Obedient plants taking over: what to do?

It is not uncommon for false dragonheads to spread rampantly. Fortunately, they have a shallow root system, so it is easy to remove the roots and rhizomes with a garden hoe. We recommend radically pruning close to the ground in autumn to keep these plants under control. Removing wilted flowers stops the plant from seeding. Alternatively, you can prevent obedient plants from taking over by placing a rhizome barrier in the soil before planting these plants.

Are obedient plants hardy?

All obedient plant varieties are quite hardy and tolerate temperatures down to -28 °C. Nevertheless, it is important to protect these plants from the cold and frost. Covering the soil around the plant with brushwood does the trick. Alternatively, plant Physostegia virginiana next to evergreen neighbours like cherry laurel (Prunus laurocerasus) to protect against frosty winds. Placing these plants against a south-facing house wall can also help by protecting them from cold wind and preventing the stems from bending. Place pots on insulating material like wood or coconut mats, or wrap the pot in a fleece blanket.

Propagating obedient plants

There are several successful ways of propagating obedient plants. As previously mentioned, it is possible to use your own obedient plant seeds. However, the easiest way to propagate is by cuttings:

• In spring, cut off long, terminal and young shoots, approx. 15cm in length, directly below a leaf node
• Remove lower leaves
• Plant the cutting in a pot with growing soil
• Always keep the shoot moist to encourage roots to grow
• Once new leaves have formed, replant your young Physostegia virginiana in a bed or container between spring and autumn

Are obedient plants poisonous?

Obedient plants contain no known toxic substances, so are generally not considered poisonous. It is therefore safe for humans, cats and dogs to be around with them. However, as they are not edible plants, we advise against consuming them.