Muhlenbergia: planting, growing and caring

Botany and description

The genus Muhlenbergia belongs to the Poaceae family (grasses) and was named in honour of the American botanist of German origin Gotthilf Heinrich Ernst Muhlenberg (1753-1815), who made significant contributions to plant classification in North America. Muhlenbergia species are primarily native to North and Central America, but some are also found in Asia. They are mainly found in arid or semi-arid regions such as dry prairies, savannahs, scrub vegetation and rocky areas. However, some species also occur in slightly more humid zones, such as riverbanks and mountain slopes.

There are approximately 170 species of Muhlenbergia, the most well-known and commonly cultivated being:

• Muhlenbergia capillaris (Pink muhly grass): the most popular for its airy pink inflorescences.
• Muhlenbergia rigens (Deer grass): more rigid, with golden tones, it is adapted to drier environments.
• Muhlenbergia lindheimeri: a bluish grass with silvery spikes, widely used in landscape gardening.

Mulhenbergia capillaris, Mulhenbergia rigens (photo Wikimedia Commons- Stan Shebs), and Mulhenbergia lindheimeri

The habit of Muhlenbergia is graceful and upright. These grasses form dense, erect clumps, often creating rounded tufts. The plant’s height varies by species, typically ranging from 60 cm to 1.20 m. The flexible, lightweight nature of the leaves and panicles gives them an exceptionally airy and elegant appearance, perfect for adding movement to the garden, especially when swayed by the wind.

Muhlenbergia have a fibrous, dense root system. These running roots allow the plant to anchor firmly in poor, dry soils. Their roots are well adapted to arid environments, enabling them to quickly absorb water after rainfall. This system contributes to their drought resilience.

The foliage of Muhlenbergia is one of their main decorative assets. The leaves are long, slender and ribbon-like, ranging from 30 to 90 cm depending on the species. Their texture is generally soft, slightly rough to the touch. Colour-wise, they display shades from green to blue-green, sometimes with silvery highlights. In autumn, they take on golden or brown hues, enhancing their ornamental appeal. Moreover, most species are evergreen, retaining their foliage year-round and providing visual interest even in winter.

The inflorescences of Muhlenbergia are often spectacular and airy, appearing as delicate, misty panicles. The floral spikes, extremely fine and almost thread-like, create a unique visual lightness. Colours vary by species, ranging from bright pink in Muhlenbregia capillaris to silvery or golden tones in M. rigens and M. lindheimeri. Flowering occurs in late summer and early autumn, creating a beautiful misty effect that adds movement to the garden. The small, discreet flowers are clustered in tight spikes, but it’s primarily the finesse and elegance of the inflorescences that catch the eye, especially when present in large numbers.

Mulhenbergia rigens (photo Matt Lavin)

Our favourite varieties

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Planting a Muhlenbergia

When to plant?

The best time to plant a Muhlenbergia is in spring or autumn, when temperatures are mild and the soil is still moist enough. This allows the roots to establish well before periods of intense heat or cold. Avoid planting in summer, as drought and heat could stress the plant before it is properly rooted.

Where to plant?

Muhlenbergia thrives in sunny positions, ideal for promoting abundant flowering and dense foliage. They can tolerate light partial shade, but too shady a spot may limit their flowering and reduce the plant’s aesthetic appeal.

Muhlenbergia is highly tolerant of poor soils, making it adaptable to many situations. It grows well in dry to moderately dry soils, with good drainage. The ideal soil should be slightly sandy or gravelly, with good drainage. They do not tolerate waterlogged soils, which could cause root rot. They can withstand some salinity, making them suitable for coastal gardens.

A lush border, where Muhlenbergia mingles with other ornamental grasses

How to plant Muhlenbergia?

In the ground

• Soil preparation: Loosen the soil well to a depth of about 20-30 cm to allow good root establishment. If your soil is heavy or clayey, add gravel to improve drainage.
• Spacing: Plant your Muhlenbergia with 50 to 60 cm between each young plant. This allows the plant to spread and avoids excessive root competition.
• Planting: Dig a hole twice as wide as the root ball and of equal depth. Place the plant in the hole and backfill with compost mixed with garden soil. Firm lightly and water well after planting.
• Watering: Water regularly for the first few weeks to help rooting, especially if planting in spring. Subsequently, Muhlenbergia is highly drought-resistant and requires little watering.
• Mulching: To suppress weeds and retain moisture, add a layer of mulch around the base, without smothering the crown of the plant.

In pots

Muhlenbergia adapts well to container growing. Choose a pot 30 to 40 cm deep and wide for smaller species like Muhlenbergia capillaris, or 50 cm for larger ones like M. lindheimeri. Opt for terracotta pots for better soil aeration, or resin pots for their lightness. Ensure there are drainage holes and add gravel or clay pebbles at the bottom to prevent excess water.

Use a universal potting mix or Mediterranean plant compost, adding 30% sand or pumice to improve drainage. Also mix in some garden soil with light compost to enrich the substrate without making it too compact.

Muhlenbergia has a dense root system, so it can remain in the same pot for a few years, but after 2 to 3 years, it is advisable to repot the plant to refresh the substrate and give the roots more space. Choose a slightly larger pot at this stage.

Maintenance and Pruning of Muhlenbergia

Watering

• First year: water regularly after planting to encourage good root development, especially during dry spells.
• Subsequently: once established, Muhlenbergia is drought-resistant. In pots, monitor substrate moisture more frequently.

Fertiliser

Muhlenbergia does not require fertiliser. A compost application in early spring is sufficient.

Pruning

In late winter or early spring, prune the plant to about 10 cm from the soil to encourage new growth and remove dry leaves. No need to prune during the season, except to remove dead or damaged parts.

Potential pests and diseases

Muhlenbergia are particularly hardy and resistant plants, rarely affected by diseases or pests. However, certain situations can cause problems.

Root rot

This may occur if the soil or pot has poor drainage, leading to water accumulation around the roots. Symptoms include yellowing leaves and slowed growth. To prevent it, ensure the soil is well-drained and avoid overwatering.

Aphids

Though rarely a major issue, they may occasionally infest young shoots. Aphids feed on leaf sap, causing deformation. A strong water spray or black soap treatment can eliminate them.

Scale insects

These pests may occasionally attack stems or leaves, forming small white or brown bumps. Scale insects can be treated with plant-based oils and black soap.

How to propagate your Muhlenbergia?

Propagation by Sowing

Sowing is more complicated than division, but allows you to multiply a large number of young plants at once. The characteristics (shape and colour of the plant) may vary slightly.

• Seed harvesting: seeds can be harvested after flowering, in autumn. Wait until the flower spikes are dry before picking them.
• Sowing period: sowing is generally done in spring (April-May), when temperatures begin to warm up.
• Substrate: use a light, well-draining potting mix, ideally mixed with a bit of sand to facilitate germination.
• Sowing depth: sow the seeds on the surface of the soil or barely covered, as they need light to germinate.
• Conditions: keep the substrate moist (but not waterlogged) and place the sowing in a bright spot. Germination may take 2 to 4 weeks, depending on conditions.
• Transplanting: once the seedlings have a few leaves and are sturdy enough, transplant them into individual pots or directly into the ground.

Propagation by Division

Division is the quickest method, especially if you want to reproduce a specific plant (same colour, same shape).

• Ideal period: division is preferably done in spring or autumn, when the plant is dormant.
• Preparation: choose a well-developed clump, at least 2 or 3 years old. Carefully lift the plant from the soil using a spade, taking care not to damage the roots.
• Division: use a sharp knife or spade to divide the clump into several sections. Each section should have several stems and a good root system.
• Replanting: immediately replant the divisions in well-drained soil or in pots, ensuring the roots are well spread out. Water generously after planting to help with rooting.

Association with Muhlenbergia

To create a harmonious border with Muhlenbergia, a great idea would be to mix the pink hues of Muhlenbergia with blue flowers and a few touches of yellow, creating a striking contrast. Alternate plants with fine, airy foliage with species that have denser foliage and produce compact flowers, such as sedums. It’s also important to leave enough space around the Muhlenbergia to showcase their airy panicles and prevent them from being overwhelmed by larger plants.

In this border, you can create subtle harmony by playing with textures, colours, and the movement of different plants. At the centre, Muhlenbergia capillaris, with its delicate pink, wispy inflorescences, will add a striking lightness. Around these grasses, the addition of a few clumps of Gaura lindheimeri ‘Rosy Jane’, with their pink flowers floating above the foliage, will enhance this sense of softness and movement.

To structure the whole, the inclusion of 4 or 5 Echinacea purpurea ‘Summer Cocktail’ will provide an interesting contrast with their large purple flowers and orange centres, adding a more solid touch. Beside them, Hylotelephium spectabile ‘Autumn Joy’, with their fleshy pink inflorescences, will add volume and visual stability while balancing the lightness of the other species.

Finally, Verbena bonariensis ‘Lollipop’, with their slender, airy stems topped with small mauve flowers rising gracefully, will harmonise perfectly with Coreopsis verticillata ‘Zagreb’, whose bright yellow flowers will add luminous touches and attract pollinators.

Gaura ‘Rosy Jane’, Muhlenbergia capillaris, Coreopsis verticillata ‘Zagreb’, Sedum ‘Autumn Joy’, Verbena bonariensis ‘Lollipop’ and Echinacea ‘Summer Cocktail’