Summer’s here

A worried phone call from my Dad he wants to know why his newly-planted clematis has collapsed almost overnight, the leaves and stems wilting dramatically even though he has been watering regularly.

This is an easy question to answer, since there is only one disease that strikes clematis in this way, it's called wait for it Clematis wilt!

Unfortunately, the problem is not so easy to solve as it is to identify. Wilting is caused by a fungus, which is thought to block off the water-conducting tissues in the plant stems, causing the affected plant to collapse.

Clematis wilt is well known to gardeners and the only effective remedy is a cultural one. New clematis must be planted three or four inches deeper in the ground than they were in the nursery pot; this means that if wilt does attack there is a fair chance of the plant re-shooting from the rootstock the following season. My Dad, who is a reluctant gardener at best, is not impressed.

One or two other insidious pests have crept almost unnoticed into my garden this month including blackfly, which have infested the tall flowering stems of the cardoons. Blasting them off with a jet of water from the hosepipe is quite effective, but recently I have noticed small birds - blue tits and coal tits mostly - perching on the stems to pick the aphids off. Either way I don't feel any need to spray them with chemicals, though there are several sprays on the market that will kill blackfly along with other species of aphid.

A potful of Nicotiana langsdorfii has been attacked by some kind of leaf-sucking thrip or capsid bug. Even with the aid of a hand lens and reading glasses I have been unable to pinpoint the culprits, so I'm hoping they have all matured and flown away. The leaves are full of tiny holes, the leaf margins have rolled up and the leaf edges and shoot tops have turned brown. This type of infestation is often encouraged by hot and dry conditions and I have almost certainly aggravated the situation by failing to water this particular pot often enough (it's a long way from the water butt).

There is powdery mildew on the leaves of one of my courgette plants. This is a fungus that likes hot, dry conditions and as the true British summer begins to assert its usual cool, damp self I think the mildew will disappear (though it may well be replaced by downy mildew, which prefers cold, wet summers). I will cut off and destroy the affected leaves to reduce the spread of the fungus, although the other five plants still look fine and healthy.

Jobs for this week:

Summer prune plums and cherries, shortening side shoots by about two thirds.

Continue to feed pots of lilies after the flowers have finished, in order to build up the bulbs for next year.

Lift and dry shallots and autumn sown onions that have finished growing and ripening their bulbs.