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Is it safe to repot my elderly Strelitzia?

QMy bird of paradise plant is 25 years and has flowered every year despite never being repotted. I think it needs a new pot, but what compost should I use?

Dorothy Loveridge, Old Basing, Hampshire

A What a splendid Strelitzia reginae and how marvellous that it has performed so well. It would, however, certainly benefit from being repotted. If it has outgrown its existing container and the roots are pot-bound, reset it in a pot 8in (20cm) larger in diameter than its current one.

Start by using a hand fork to tease apart the rootball, especially if the roots are starting to grow in a circle. Then cover the new pot’s drainage holes with crocks or stones and fill it with 4in (10cm) of a mix, by volume, of three parts John Innes potting compost No3, and one part coarse grit.

Reset the rootball at the same depth at which it was previously growing and cover it with more compost. Gently firm it around the sides with a thin wooden ‘rammer’ to avoid air pockets.

Leave a 2in (5cm) gap between the top of the compost and the rim of the pot to allow for watering.

Ideally, cover the top of the compost with slate chippings to stop the compost