Plant Doctor Archive

Ailing michelia

I HAVE enclosed some leaves of my two Michelia doltsopa trees which I planted in July in remembrance of my mother. Some of their older leaves are yellowing and dropping off, though there's new growth which is green and healthy. The soil here is stony and hard, but I've kept them well watered, fed with Osmocote at planting and given them a weekly feed with liquid Thrive. We get a lot of wind - could this be the problem? I also wonder about the wooden stakes I used to stabilise them. I bought them at the garden centre, but I wonder if there's some treatment in the wood that may affect the plants.

THE leaves you sent showed no signs of pest or disease, so it looks as if the michelias are just taking time to settle in and recover fully from being planted out, which is quite common for this species.

Many evergreen trees do lose a few leaves after planting, particularly if the site is windy and the soil poor, as it is in your case. Also worth bearing in mind is that many evergreens, including michelias, will lose some leaves as part of their normal annual cycle.

You're doing the right thing with watering - make sure to keep it up over summer and apply a mulch, such as pea straw or bark, around them to help keep the moisture in. I also recommend cutting back on the liquid fertiliser until they have established a really good root system, which could take another six months or so. The aim at this stage is to encourage root growth rather than soft top growth.

The stakes should not cause a problem. Timber treatments only rarely affect plant growth. But make sure to check the stakes don't rub against the trees in a strong wind.

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