Tag Archives: collar rot

Garden lore: don’t do this at home

img_3822Well lookee here. When I was submitting three new articles a week to the Waikato Times – that was in the days before syndicated features and the resulting copy that became the newspaper equivalent of elevator muzak – I used to be on constant alert for subject matter. Old habits die hard and I reached for my camera to bring you this example of what not to do, photographed on a street in Auckland’s upmarket Mount Eden.

Don’t. Just don’t do this at home. The homeowner is disposing of lawn clippings by building a small grass mountain around the street tree on the road verge outside. It is not good for the tree and may even kill it over time. Building that mound can cause a condition called ‘collar rot’ – opening up the tree to fungi that attack the bark around the base of the tree. Bark needs to breathe, not be suffocated. Grass heaps also heat up as they start to decompose and that heat is bad for the tree, potentially killing the bark. Then the grass compacts down to an anaerobic sludge which can suffocate the surface roots. All this just so the homeowner doesn’t have to put their grass clippings out in the green waste or to find ways to compost it on his or her own property? Tidiness is not everything in the world of gardening and nature.

Garden Lore

“Now that all the other many-hued flowers have scattered without a trace, the dead white head of the miscanthus remains alone in the fields until the end of winter. As it stands there so gracefully, not realising that it has entered its dotage, and bending its head as if in memory of past glories, it looks exactly like a very old person, and one cannot help feeling sorry for it.”

Sei Shonagon The Pillow Book of Sei Shonagaon (tenth century, translated by Ivan Morris 1967)

023Garden Lore: Mulching with lawn clippings

Naturally I stopped to look at this magnolia tree in a garden in Auckland. I was trying to work out if it was our Magnolia Black Tulip, bred here by my Mark. I think it was but I was so disturbed by the grass clippings beneath that I wanted to knock on their door and proffer advice. There is nothing wrong with using grass clippings as a mulch but with two provisos.

Most importantly, keep the clippings clear of the trunk of the tree. The main risk is opening up the tree to collar rot by encasing the trunk in warm, moist material. This enables fungal disease to get in, damaging the outer tissue of the stem or trunk. This can be fatal over time and the tree is likely to show damage by dying from the top down.

Keep the clippings to a relatively shallow depth, maybe 10cm. Grass can generate quite a bit of heat as it starts to compost and few plants appreciate their roots and trunks or stems being heated. In this case, I think they have the grass clippings piled on much too deeply and they are probably adding to them regularly. At the very least, clearing a breathing space of a few centimetres around the trunk would be good practice to avoid potential problems. Prevention is always better than scrambling to find a cure when one suddenly realises the tree is looking sick.

First published in the Waikato Times and reprinted here with their permission.