Should I divide bearded irises?

Q We would like to rescue some bearded iris growing in a neglected and overgrown border. They look quite healthy, but haven’t been flowering. Will they need to be divided, when is the best time, and how is it done? Fran Dickinson, King’s Lynn, Norfolk

- Anne Swithin Banks

A We all know it doesn’t take long for weeds to take over an untended border, but luckily, bearded iris are adept at staying alive until someone comes along to rescue them. They are known as ‘flag’ iris and their sword-like leaves will wave like flags above a sea of weeds to let you know where they are. What they won’t do is a flower, because weeds and debris will have prevented the sun baking their rhizomes.

Proceed with caution to cut rather than pull off any ivy and brambles that might tighten and rip the iris leaves, then grub away grass and weeds until you can see the rhizomes at soil level. The best time to divide bearded iris is within six weeks of them having flowered, and before August, when they set their flower initials. I would take action now, because in a neglected border the rhizomes are going to have to come up in order to extract weeds from around them. Fork the bed and add bone meal. As long as the soil is well drained and the border is in a sunny position facing south or west, the prepared plants can return to the same place.