- Rotate clipped evergreens in pots, where possible, so that they receive sun and stay dense and green all over. Feed them with a general granular fertiliser; old hedges, too.

- Cut out the flowered stems of that great stalwart, Euphorbia characias, to give light and strength to the new stems. Leave the odd one to throw out its seed if you want seedlings. Remember that the sap marks the skin and some people can be allergic to it, so use gloves.

- Cut back to new shoots the flowered stems of sprawling helianthemums. More flowers will follow.

- Some roses in some gardens never stay clear of mildew or rust. If you are spraying them regularly to control fungal disease, change the chemical every couple of months, to avoid immunity.

READERS' QUERIES

Over the past months, I have noticed that the foliage on my 20-year-old conifer tree has started to turn brown. What’s happening, please? Mr P. Draper, Purley, Surrey

When two apparently healthy specimens of the same plant stand side by side (in your photograph, two 3m upright cypresses, probably Chamaecyparis ‘Ellwoodii’) and one of them quickly dies back all over, then the problem is usually root disease or poisoning of some kind. Something has stopped the roots functioning and the plant turns brown and dies of thirst; the leaves stay on, whether it’s evergreen or deciduous. Now, if a deciduous tree suddenly droops and browns it’s very conspicuous, of course; but if it’s a conifer, the browning process is more gradual, and that’s when it’s tempting to think there are other forces at work – pests and so on.

Your dying (let’s be frank, dead) tree I see has had its top sawn in the last few years, presumably to restrict its height. Big question: did you do it, or was it your neighbour at dead of night (I never said that)? Either way, taking out the main trunk of a conifer and leaving a fat wound to the trunk can sometimes cause fungal dieback, which will polish off the tree – think cutting off an arm rather than finger nails. That’s why it’s always better to cut only into youngish wood (think topiary as manicure). I’d get your tree out and give its neighbour the chance to spread its wings.

Would it be possible to cut a begonia tuber into pieces and grow each piece in a similar way to potato tubers? J. Slator, Oswestry, Shropshire

Certainly you can do that, just like a potato, but you can’t go carving through its vital organs when it’s in leaf. The time to do it is in early spring, once the little “potato” sprouts have first appeared. Cut the tuber into two to three pieces, dust the cuts with flowers of sulphur (a fungicide) and leave to dry somewhere cool and dark before planting them. Clean cuts make for better healing.

It’s the same with bearded irises: when you divide the rhizomes after flowering in the next few weeks, leave a clean-cut end to the rhizome, not a torn one, and let it dry for a day before replanting; older, tougher varieties don’t give a damn what you do to them, but some of the fancier, fussier modern varieties can rot so easily.

stephen.anderton@thetimes.co.uk

Explore Gardens

• Hampton Court Palace Flower Show

• Chelsea Flower Show

Times recommends

• Second homes: credit crunch casualty or money-spinner?
• How I built my own sliding house
• Top 10 incentives for house buyers