Reader Queries:

Q: I have in my garden a deodar cedar which I planted about 20 years ago. It has now reached a height of over 20ft. Is it possible to reduce the height without doing damage to the tree? - Mr J. Clamp, Greens Norton, Northants

A: Mature conifers of the “Christmas tree” form do not respond well to having the central trunk cut back. They may sprout out again with a modicum of grace after removing 2ft-3ft, but in principle you are still ruining the tree’s form and it will remain to haunt you until you have the courage to remove it altogether. Have it out now. No garden tree is sacred; far more important is to be always planting the next generation.

Q: My lawn has been burnt to a crisp by last month’s heat and drought. What is the best way to bring it back to life, or do I have to start again? I only laid it last year. - Mrs H. Gifford, Chelmsford

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A: It is astonishing how well a lawn will recover from such an ordeal, as long as you are kind to it. It is important to keep off the grass as much as you can while it is brown so that the roots are not worn away by feet. My lawn has been so frazzled in places that it crunched as you walked on it, as if it were covered in frost. I have been under a hosepipe restriction from the start of the season, but I never water lawns anyway; they recover. I did put a can now and then on the places where we step off paving on to the lawn, to prevent the destruction of the roots.

As the rains return, turf will put out new shoots, gradually and patchily. When it starts to look spiky, top it off with a light mowing at 2in; only when it is really growing and the ground is moist for at least 6in below the surface should you give it a light dressing of fertiliser. Use a proprietary low-nitrogen autumn feed.

Q: In our front garden we have a robinia pseudoacacia ‘Frisia’ which is now growing through the overhead power lines. We have had the tree pruned a couple of times, but this only encourages it to grow even more. Can you suggest another tree that would be more manageable, but which would be as beautiful as the ‘Frisia’? - Mrs M. Taylor, Tamworth, Staffordshire

A: What are you after? Another tree with lacy foliage that’s yellow in summer? I have to say that, striking though the yellow foliage robinia ‘Frisia’ is, it’s not exactly generous – not much flower, no berries, and no special autumn colour – but it is good in hot, dry soil. If you want a smaller tree for those conditions, which is delicate and flowers yellow in summer, try the Mount Etna broom genista aetnensis. If you want a complete change, try a good crab apple such as crataegus ‘Prunifolia’, which will offer you good flower, fruit (so there’ll be birds, too) and autumn colour.

Q: Where can I get hold of yellow thistles? - Mr A. Preece, Hereford

A: There is the odd wild thistle that’s yellow, but I bet you mean centaurea macrocephala, which is actually a big, soft, garden knapweed, though it does look pretty thistley with its scaly cup and big tuft of stamens. It couldn’t be easier to grow, and it’s fine for the middle or back of a sunny border. The flowers don’t last especially long, but it’s nevertheless unusual and attractive; an old cottage favourite. Highfield Nurseries sells it: 01452 740266; www.highfield-nurseries.co.uk.

On the other hand, you might mean the prickly poppy argemone mexicana. This one is an annual grown from seed. I have it in my garden. Each year I think it’s disappeared, then in late May seedlings appear again. The flowers are clear-lemon saucers and the leaves greyish with white veins. The spines may not be big or hard, but they’re tricky to get out of your skin. Even the seed pods are prickly, and look wonderful dried. Chiltern Seeds sells it: 01229 581137; www.chilternseeds.co.uk .

Q: Last year I bought a pot of rich-blue agapanthus to go in the middle of a border. It has produced few flowers, which are only a foot high, hidden by other flowers. Why? - Mrs C. Morell, Oxford.

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