Pat sent me a problem last week about her Magnolia grandiflora ‘Exmouth’, which she bought from Birch Grove Garden Centre two years ago and planted in a tub against a south wall.
Last year it did splendidly, and put on a good amount of growth, but this summer the leaves are starting to discolour in the middle and drop off, although new growth is beginning to appear.
From the picture, I think this unhappy shrub needs a bigger container – a large half-barrel or similar, as most of the damage seems to be stress related, through the magnolia, which, planted in open ground, makes a good-sized tree in time, not having a big enough root run.
The damage on the leaves looks like scorch from our exceptional recent hot sunshine, or maybe even frost damage during the winter which is only just beginning to show because of prolonged high temperatures.
It certainly isn’t dead. I would find a suitable container and re-pot it immediately in a lime-free, soil-based compost.
Even better would be to lift a slab in the path and replant it in the ground, replacing the soil in the area with ericaceous John Innes compost or similar to get it off to a good start.
It will need watering regularly for the rest of the summer, adding a weak liquid feed about once a fortnight. It should then start to show an improvement within weeks.
Magnolia grandiflora does not need the same sort of conditions as rhododendrons and other acid-lovers, although it won’t thrive in chalky soils, or soil around house walls, which often contains a lot of lime from the cement used in constructing the property, hence my recommendation to replace it under the slab. Given the right treatment, it will make a stunning wall shrub, although it may take a few years to start flowering.