Plant Doctor Archive

Poorly Knights lily

I HAVE a large xeronema which has been growing in the same raised bed for 25 years where it has thrived with dark glossy spears and lots of flowers. However, over the last six months or so it has started to show brown rot at the base of each group of spears and the entire plant is collapsing. Even a piece I took off two to three years ago and planted some distance away has started showing the same symptoms. Could this be a fungal disease?

XERONEMAS, aka Poor Knights lily, require extremely free-draining conditions and can go for months without water. A mistake many people make is in thinking you can make them grow better and faster by watering during summer.

According to well-known plantsman Terry Hatch, watering xeronemas in hot weather can cause root problems and rot at the base of the plant. He recommends the fungicide Foschek for controlling root diseases of this type - it's available from horticultural suppliers such as Veg-Gro Supplies Ltd. Or you could try No Root Rot, stocked by most garden centres. Follow the label instructions.

Otherwise, allow the plant and soil to get as dry as possible and, instead of watering in summer, apply a mulch of granulated bark or pebble chips which not only improves soil condition but reflects heat in a similar way to the rocky areas where these stately plants thrive on the Poor Knights and Hen Islands. They also require exposure to full sun, so check if nearby shrubs or trees are casting shade and prune if necessary.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.