Reader Queries:

Q: Our healthy lavender bush was invaded at the end of May by evil little shiny blacky-green beetles that are decimating the foliage. I've taken to picking them off and squashing them individually, but its grossing me out and I feel a more permanent solution would be preferable! - Mrs L. Priddle, London SW11

A: Your rather handsome pest is rosemary-leaf beetle, chrysolina americana, which is just as keen on lavender as it is on rosemary, and a serious problem. It has probably done its worst for the time being, since it rests among the foliage during the summer months. If you can bear to hunt it down now and continue squashing, it would pay off later — just imagine you are popping bubble wrap. Come August, it will wake up again, appetite ablaze. In a couple of weeks there will be eggs, then larvae, then pupae developing in the soil; five weeks can see a whole new generation chomping away, beetles and larvae alike.

So, if you have had your fill of "grossing out", August is the time to spray with bifenthrin or imidacloprid, such as Provado Ultimate Bug Killer Ready to Use. Avoid spraying while the plant is in flower, for the bees' sake. Incidentally, the beetle first appeared at the RHS garden at Wisley in 1994 and can now be found as far north as Edinburgh. Such is the price of the international exchange in plants.

51 glorious garden websites

Times Online's gardening guru opens her address book to share her top pick of gardening websites

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Q: What could I grow at the foot of an old box hedge to spread out on to a stone path in front of it? - Mrs B. Whitrow, Kenilworth

A: Life is dry and hungry under an established hedge and anything you plant will need regular watering and feeding until it is established; better to plant in autumn if you can't do that. I would try one of the acaenas — they would pool out nicely over the paving and the little burr flower heads are fun. 'Blue Haze' is a steely blue-grey and 'Kupferteppich' a coppery bronze. If it's shady, try London Pride (Saxifraga x urbium).

Q: I planted a tree peony in my garden six years ago. It has never produced any flowers, despite its vigorous leaf growth. Last autumn, I cut it back quite severely in the hope that it would produce blooms this summer. Despite this, and adding fertiliser around the base of the plant in early spring, it still shows no sign of flowering. It’s about 8ft high. I’m willing to give it one more year, but after that, that’s it! - Mrs J. Condliffe, Blewbury, Oxon

A: A tree peony that grows so easily and happily to that height must be the yellow Paeonia ludlowii. It produces masses of fat black seeds and that is how it is usually propagated, so there is often variation in the progeny, for better or worse. Some have really miserable little flowers, some are fine. As long as your plant has good light and is growing healthily (remember, the foliage is always pale green) then, if it does nothing next year, write it off as a dud and scrap it. No pruning in the meantime – hard pruning positively discourages flowers.

Q: In June last year, I followed your advice and grew a crop of morning glory ‘Heavenly Blue’ from seed, in a pot and against a stone wall. As there were still lots of buds at the end of October last year, and as the packet suggested sowing indoors in April, that is what I did this year, hoping to get a longer flowering season. The seeds germinated quickly and I hardened them off outside, transferring them to the large pot during the hot weather at the end of April. Since then, they haven’t made much progress and look rather unhealthy and yellow, despite watering. Do you have any suggestions? - Mrs E. Allchurch, Redditch, Worcs

A: Isn’t it a glorious sky blue? It’s wonderful scrambling up among the stems of the hardy passion flower passiflora caerulea when the apricot-coloured fruits have formed. But it’s one of those annuals that hates to be chilled by too early a start or a cold spell once it has been planted out. Next year, stick to sowing them well into May or even in June; I would be tempted even to try them now. Soak the seeds for half an hour before you sow, and get the young plants out into the garden as soon as they’re strong enough.

Q: A few years ago you visited our garden for The Times Back Garden of the Year competition and saw our avocado tree, which was grown from a “pip” 24 years ago. It is now so healthy at some 20ft tall that we have had to engage a tree surgeon to prune it. This year for the first time it has flowered, and we welcome your advice as to whether it may fruit. - C. and T. Scorer, Dartmouth

A: Wonderful. I have not seen one flower in the UK, but I doubt it would fruit here; it likes a generally warmer climate, not just seaside mildness. The flowers also have the funny habit (polygamy) of putting out pollen one day and being ready to receive it the next, so it’s best to have more than one tree for good pollination. If you have the tree heavily pruned, of course, it will shoot all the harder and be less likely to flower again for a few years. Keep me posted. It would be interesting to hear if other readers in the UK have got any further than the flower stage.

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