Anne Swithinbank’s Masterclass

QI’ve read that ornamental grasses should not be planted or moved during autumn, as spring is the best time. Is this true, as I’d like to put some in now? Jill Thurrock, Cheltenham, Gloucestershire

AThis is both true and false, as ornamental grasses are divided into two sorts for cultivation purposes. Those known as cool season grasses begin their growth in late winter and produce flowers by midsummer.

Examples include the showy golden oat grass (Stipa gigantea) and shadetolerant Bowles’ golden grass (Milium effusum) ‘Aureum’. It’s generally thought that they establish better from an autumn planting than a spring one.

As with everything in gardening, advice is tempered by soil and climate. On well-drained soils or in slightly raised beds – and as long as they are planted by mid-autumn – these cool season grasses should take well. Yet on heavy soils like mine, which are often wet and cold during winter, I would delay planting until spring and would not risk lifting and dividing grasses such as festuca past the end of September.

I suspect that you want to plant warm season grasses such as panicum and miscanthus, because they look so good at this time of the year. Flowers fade and persist well, add softness and movement, and look great decorated by dew or frost and snow. Yet these warm season grasses go dormant during winter and don’t start back into growth until late spring or early summer. Not surprisingly, they are mainly sun-lovers, relishing warm, sheltered spots.

As a group, they don’t take well from an autumn planting and tend to sit, mope and potentially rot away during the long wait for their growing period to start. Far better then, to buy fresh, healthy plants in spring, condition soil with sharp grit if better drainage is needed, and get them in just as new growth is showing. The same goes for lifting and dividing existing plants.

On the whole, grasses prefer poor, well-drained soils – as anyone with clay soil who tries to grow billowing Stipa tenuissima will testify; they often rot, to be replaced by seedlings. On wet, heavy soils, stick to sedges.