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Thorny problems: pond trouble <>b (Filed: 02/06/2001) Helen Yemm tackles some murky waters

Keep suckers at bay

The shoot tips on my 6ft bay tree have become disfigured with what looks like a white mould where the leaves have curled over. Last year, I cut them off, hoping that I had cured the problem, but I obviously didn't. Jane Miller

The damage has been caused by a tiny insect called a bay sucker, which takes up residence in early May to breed. The white woolly stuff under the leaves is a protective secretion produced by their babies or "nymphs".

Cutting off the shoot tips and burning them should help. But if you do it too often, later in the season your bay tree will not flower, which would be a shame as it is about the only interesting thing a bay tree does. You should also grub out all the old leaves from underneath the bush.

As you have already discovered, the problem does tend to go on from year to year. Harvest as many leaves as you need for the year and spray the bush with a systemic insecticide (Doff makes one). As a precaution, harvest and then spray the bush again next April, before any bay sucker nymphs that dare to show their faces can do any damage.

A plant worth its salt

I live in a fourth-floor flat with an 8 sq ft balcony, south-facing but breezy. What can I plant? I don't want to settle for a row of little pots round the edge. Mrs Ann Warren, Poole, Dorset

This is one of the cases where I am so grateful that you provided a full address, as it gives me a good idea of your problem - namely, salt-laden "breezes", occasionally of some ferocity, coupled with the closest we get to blistering sun.

You are right to aim a bit higher than "a row of little pots". Balconies can become horribly cluttered and time-consuming, so less is more. I suggest you go for one major shrub in a tub - a tough evergreen that can cope with the exposure and won't flap around irritatingly on windy days.

The container should be lightweight, non-porous (so it won't dry out too fast) and at least 18in deep and wide to give the shrub room to grow. Compost should be a 50:50 mixture of John Innes no. 3 and a lighter, multipurpose one.

My favourite plant for exposed sites is the felty grey-leafed Senecio greyi (now called Brachyglottis), which bears loud yellow daisies throughout summer. Rigorous deadheading and annual spring pruning would keep it in check.

Olearia ilicifolia, another evergreen "daisy" bush, would do well too. Its matt greyish leaves are slightly prickly. Pruned after flowering, it could be kept reasonably small. Some of the medium-size hebes would also work well.

In spring, you could tuck a couple of seeds of the giant climbing nasturtium into your container to give colour in later summer.

Peril in the pond

Six weeks ago the water in my goldfish pond, which has a small fountain and gets a lot of sun, was beautifully clear. Now it is green and murky and the Canadian pond weed seems not to be flourishing. Fay Jones

In all probability your pea souping is temporary. At this time of year water temperature rises quite sharply and algae multiply.

It is mayhem in there for a few weeks until the biology sorts itself out and the oxygenating plants (such as your Canadian pond weed, which dies back substantially in the colder months) get growing again.

However, there could be other forces at work. Fountains don't do much to aerate a pond and if yours is very sunny you may well have a green-water problem. You need to ensure that the oxygenating plants take over about two-thirds of the pond area, and ideally about half of the surface should be covered with waterlilies to create shade. Have the water pH checked. You can buy a kit and do it yourself.

If it is high, this may also encourage green water. High pH can be caused by too frequent "topping up" with tap water and, in newly constructed ponds, by mortar in adjacent paving leaking lime into the water. Overfeeding your fish can make matters worse - the debris adds to the general aquatic malaise.

But don't panic and rush to fill the pond with one of the many chemical wonder cures for green water. Sit tight for a week or two and see if it sorts itself out. Your dream of glimpsing flashes of gold in your pool may yet be realised.

At least you haven't got the dreaded blanket weed.

Wrong end of the stick

D W Theakston, Bartestree, Hereford, wonders why we are advised to stop pulling rhubarb sticks after about midsummer. But think what pulling rhubarb sticks really means - ruthlessly removing the plant's leaves, its solar panels effectively, almost as soon as they are produced.

We wouldn't treat any other garden plant like that and expect it to provide the delicious substrata for crumble year after year. Even lawns get a better deal. I am sure that the advice is given in order to make us give the poor plant a chance to recharge itself for the next season.

I have also been inundated with information about shamrock, as I knew I would be. Just my luck.

I will write further on the subject in a week or two.

Write to Thorny Problems, Helenyemm1@aol.com or The Daily Telegraph Gardening, 1 Canada Square, London E14 5DT. Helen Yemm regrets that she can answer letters only through this column.

-- Anonymous, June 06, 2001