Caring for Grasses

Late winter to early spring is the time when most grasses will need some annual attention; which is fairly straightforward provided that you know which group the grasses belong to.

When it comes to pruning there are really two main groups of grasses; the evergreen group with foliage that stays alive all year, and the deciduous group whose growth dries to a beige brown but can often remain standing for the winter. A smaller third group, the semi evergreens, can exhibit characteristics of the other two groups. Most work is done from late winter into the spring so it is fairly easy to tell which is which at that time, but if unsure our online plant descriptions should be able to help.

Pruning grasses can be done by a variety of different tools as seen above. None are really better than the others, so it is a question of personal convenience though with larger areas mechanical or electrical trimmers do make the job quicker.

In most of the UK deciduous grasses, such as calamagrostis, miscanthus, molinia, deschampsia, panicum and pennisetum, are best cut back in the spring, from late February through to end of March depending on the weather; ideally just as the grasses are beginning to wake up and the new shoots are coming through. Rather like lawns, cutting any new growth at that time along with the old will not harm the plant.

When cutting back last years growth it is ideal to cut as close to ground level as practical leaving plenty of room for the new shoots to grow through quickly.

If leaving the cut stems on the ground as a surface mulch it is best to cut them into smaller sections rather than long lengths as they make a more effective mulch as well as looking more attractive.

The Mill End borders, above, just after their annual spring cut. Leaving the old growth on the border makes an attractive ground pattern as well as keeping weeds down.

When well suited to their growing conditions some longer lived evergreens such as carex, liriope, ophiopogon and acorus can need very little aftercare. These Carex Evergold growing in the garden at Knoll, above, have needed no treatment for over a decade.

When young, shorter lived evergreens such as Nassella (Stipa) tenuissima, (above), can need little looking after for the first season or two, however a quick rake through or tidy in spring can help to remove the worst of the old leaves and flowers. Once established Nassella can be cut back one or more times during the growing season. If necessary shorter lived evergreens like nassella and festuca can be lifted and divided at the same time which will help rejuvenate the plants.

With some evergreens like this short lived (3-5 years), Anemanthele lessoniana above (also known as Stipa arundinacea), they can get relatively strawy on top after a few seasons and may tolerate being cut back with reasonable success. However this must be done when the plant is actively growing in spring or early summer. Anemanthele also dislike being divided. It is often better simply to replant with younger plants.

After one or more seasons shorter lived evergreens like this festuca, above, can look a little tired in spite of raking out the worst of the old foliage. Cutting back the old tired foliage will encourage a new set of leaves but must be done in the spring or early summer when the plant is actively growing. If needed, dividing festuca and nassella at this time will further help rejuvenate the plants.

Cutting back in spring for shorter lived evergreens such as festuca can be quite hard, shearing off all the old growth to make way for the new shoots which will start to re grow quickly.

Having been cut back to a tidy mound this festuca, above, will start to sprout new foliage within a few days provided that it has been cut back in the spring or summer time when the plant is actively growing.

While evergreen in warmer areas, semi-evergreen grasses are those like Elymus and Sesleria, above, that can become effectively deciduous by the end of the winter period in the mild and damp climate of the UK. On the whole, this group will tolerate being cut back relatively hard, virtually to the ground, on a regular basis, provided that the plants have begun active growth.

Many grasses are clump forming and so while the clump may attain a fair size over a number of years it will remain in the same position. While not requiring division for many years clump forming grasses can be lifted and spilt when needed.

When required most clump forming grasses, such as this miscanthus above, can be lifted and split with a sharp spade into not too small a pieces for replanting. Spring, just as the grasses are beginning to wake up is the ideal time.

Mat forming grasses such as Carex Ice Dance, above, gradually form tough mats of roots and foliage which allow them to survive in difficult garden situations such as dry shade. These tend not to need rejuvenation in the same way as clump formers might, but smaller pieces can always be lifted to make more plants or to fill a gap.

Grasses with a running rootstock, such as Phragmites, Leymus and Phalaris for example, tend not to make such popular garden plants. However having a vigorous self renewing root system allow some, such as Carex arenaria above, to survive in testing conditions and this quality can make them invaluable for specific uses such as lawn replacement, green roofs and erosion control.

Many grasses will grow happily in containers for some years provided that the container is sufficiently large for the grass to grow well. Keeping grasses healthy in pots tends to require a repot and some fresh compost each season though a few slower growing grasses such as hakonechloa and imperata may be happy in the same pot and compost for several seasons. As with any plant should the roots run out of compost and room they will eventually slow down and the top growth will follow; hence the term pot bound.

If you cannot pot up into a larger pot then simply cut off a section of the old and tired roots to make way for fresh compost at the bottom of the pot in the spring. The roots will enjoy the new space and compost and as a result the grass should put on vigorous new top growth.

Dont forget to water all plants in pots during dry weather……