Cultivation
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.
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. 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.
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. 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. They respond badly to root disturbance, so when digging plants out of a border, minimise disruption by retaining an ample root ball. 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.
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.