Here’s a list of the best grasses or Pennisetum chosen by head gardener Matthew Reese

By Mat Reese

Published: Wednesday, 16 August 2023 at 00:00 AM

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The genus Pennisetum comprises about 80 species, mostly perennial, from sub-tropical and warm temperate regions of the world. Many pennisetum are highly ornamental grasses, and for the most part, clump-forming (a few are rhizomatous), with neat tussocks of arching foliage from which numerous fountains of plume-like inflorescences emerge from mid- to late summer. The pennisetum seedheads persist throughout the winter and the sere foliage can be an asset during the colder months when brown becomes more valuable in the garden.

With so many pennisetums now on offer, we can fully recognise their terrific garden potential. When planting pennisetum, consider how to bring out the best of the plant, either by planting in drifts, or, if your chosen species or cultivar is bold enough, leaving it to stand on its own. The lovely flowers and foliage combine well with late-summer perennials, such as asters or Helianthus.

How tall does pennisetum grow?

Small, versatile pennisetums are about 40cm tall, while larger forms grow to over 1.5m. The warmer the climate/season, the taller and larger the plants. The shorter species are particularly well suited for the front of the border. The foliage remains smart from head to toe and acts as a useful screen when placed in front of taller perennials, such as phlox, the lower leaves of which often become ragged as the season progresses.

When to cut back pennisetum

Pennisetum leaves and foliage looks lovely even over winter, so leave it til spring when you can cut back dried leaves o roughly 8 inches from ground level.

How to grow pennisetum

Although there are many new cultivars of pennisetum that are suitable for the cooler summers in northern parts of the UK, they still require a warm spot. Seek out a sunny, south-facing position, or even a sheltered location in a sun trap. Pennisetums will also be thankful for an extra boost of radiant heat provided by a wall or stone path. Most pennisetums need a temperate climate with warm summers. Although some can take drought when established, the Asian species do best in warm, moist soils that don’t sit wet in the winter.

When to plant pennisetum

Aim to plant pennisetums in late spring when the soil is warming up (a general rule true for most grasses). Avoid planting in autumn – it will be the death of the plants if you do so.

How to plant pennisetum

On planting, improve the soil by adding a slug of rich compost, mix thoroughly with the existing soil, and add grit if the site has a tendency to sit wet. In very wet gardens, plant pennisetums next to a path, or a wall where the drainage is particularly sharp. Firm the soil around the plant to prevent wind-rock and to aid drainage.

How to care for pennisetum

In the right position, pennisetums are fairly trouble-free. Young plants should be given space to breathe and competition should be controlled until the plants are established and more robust. Water the plants in dry periods until they are well rooted. They respond badly to root disturbance, so when digging plants out of a border, minimise disruption by retaining an ample root ball.

Pennisetum in pots

The quick-growing, tender species and cultivars should be given lots of sustenance and potted on regularly if grown in containers. Tender species and cultivars should be brought into a warm greenhouse or conservatory in autumn. Place the plant in a pot that closely matches the size of the root ball and provide heat. Plants will invariably suffer some dieback, which should be gently removed, but if you can keep them going, plants should recover quickly in spring.

Propagating pennisetum

Most species can be easily propagated from seed, and fresh seed will germinate quickly. Seedlings should be left to bulk up in their trays before moving them on into larger pots. Grasses should be potted on during the warmer months when they are growing. Plants generally don’t produce roots to a significant degree during the winter months, leaving them susceptible to rot if the compost is too wet. The same guidelines apply to vegetative propagation: splitting clumps should be done in spring. Discard any old, woody parts, and keep the young, outer part of the clump. The divided portions destined for the garden should be kept to approximately 15-20cm across. Any smaller pieces can be potted on.

Below you’ll find some of the best pennisetum’s to grow, chosen by head gardener Matthew Reese.

Pennisetum: the best pennistum to grow

Pennisetum orientale ‘Tall Tails’