Plant Doctor Archive

Grass tree browning

WE grew some Xanthorrhoea from certified seed in 1992. We started with 10 seeds, three germinated and only two survived. When we moved house in 1997 we took the plants with us. They've both done well until this year when one seems to be dying. Can you give us any advice?

THESE Aussie natives, often called grass trees, are very slow growing and can live to a ripe old age. In their native habitat they often get burned in bush fires. This cleans off all the foliage, leaving the trunks black and exposed to the elements. But they soon sprout new growth from the top and seem none the worse for the experience. They grow best in relatively warm, dry conditions and need free-draining soil.

In this country grass trees are susceptible to root disease brought on by overly wet soil, especially in winter when the soil is often both cold and wet. It looks as if your plant with its browning lower leaves is suffering from root rot. If the soil where it's growing does get wet at times, you should think about improving drainage or move the grass tree to a better spot. You could build a mound of gravel and bark and plant it on top - they don't need fertile soil and transplant quite well. At the same time remove all the brown leaves, cutting them off close to the base of the plant to open it up to fresh air.

You could also try spraying the foliage and drenching the root system with the fungicide aliette, which is available from garden centres as No Root Rot.

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