Q: Mary Savva wrote – I have peonies – when do I get rid of the foliage as they have finished flowering?
A: I would leave the foliage intact. Peonies have fleshy roots that benefit from being fed by their leaves throughout the summer. Also, the foliage colours up attractively in the autumn, adding interest to the border. Once this has faded you can cut the leaves down nearly to ground level (leave a centimetre or two to remind you there is something planted in that spot!).
Q: Two years ago, I bought a Magnolia grandiflora and planted it in a 35cm diameter pot of multi-purpose compost. I was hoping to train it on the south wall of my bungalow but all the leaves have started dropping off, although new shoots seem to be appearing at the top.
A: Magnolia grandiflora, left to its own devices, makes a large tree, although it can be trained as a wall shrub. The tub yours is growing in is rather small, and I think it should be replanted into a large half-barrel. The compost is not really suitable, either, as it will dry out very quickly, especially in the hot sunshine we have had this summer. I would replant it immediately, using a lime-free soil based compost, which will hold moisture much longer, so take care your magnolia doesn’t become over-watered.
Q: Why are the leaves of my garlic withering? They are also covered with rusty spots. I planted the cloves in spring and when I pulled one up recently, the new bulb was very small. They have been well watered.
A: Your garlic is suffering from rust, a disease of the onion family that is more often seen on leeks. A severe infection can be fatal, so don’t grow any members of the onion family in that piece of ground next year, and, preferably, the year after. Autumn planted garlic leaves may start to wither now, and the bulbs should be ready for harvesting, but garlic planted in spring, like yours, should continue to grow for another three or four weeks. As the rust has caused the leaves to wither, it is unlikely the bulbs will get any bigger, and as spores will be on them as well as the leaves, I think your best plant is to lift the whole crop and dispose of any bulbs immediately that are unusable. Store those you intend to use well away from areas you may grow onions, leeks and garlic in the future.
Q: What is the white, powdery stuff that is all over the leaves and new growth of many of my shrubs?
A: This is a fungal disease called powdery mildew. Although not fatal, it can damage flower buds and distort younger leaves and new shoots, and spoils the appearance of many plants. Spray with a fungicide now, and again in a fortnight. It won’t usually improve the look of plants already affected, but spraying will prevent the disease from spreading. This hot summer has been particularly bad, and next year you may not see as much, but a preventative spray in spring will help to control it.
Q: The leaves on my ‘Swift’ early potatoes have turned yellow and started to die. Is this potato blight?
A: It’s unlikely you will see blight on early potatoes and the problem is much more likely to be shortage of water. Lift your potatoes now and enjoy them, although I expect they will be very small. If you are growing main crop varieties as well, keep them well watered until lifting in the autumn.
Q: I have a ‘Brown Turkey’ fig growing in a large pot. Last week a visiting youngster rode his bicycle into it and broke off a branch. It started to leak a sticky white liquid from where the branch was broken off. Will it die?
A: No, the latex produced by the fig should have sealed the damage quite quickly and there should be no lasting problems. Many people are allergic to fig sap, though, so to be on the safe side, keep it off the skin when pruning or after accidental damage such as this.