[OG Note: Every British child is familiar with fairy rings. They are rings of toadstools or mushrooms which pop up overnight and are known to have been put there by fairies who were holding a nocturnal conference--no doubt formulating a mission statement. They are also rings of dying grass, caused by fairies dancing.]

Thorny problems: fairy rings (Filed: 23/06/2001)

Gardener and lecturer Helen Yemm on curing your lawn with Epsom salts

Fairy rings on lawns

I HAVE a huge fairy ring on my cherished lawn, and I read, years ago, that Epsom salts could be used as a cure. If so, how should it be applied? Or if not, is there a less disruptive solution than digging up the lawn and applying chemicals? Mary Fotheringham, Colchester

I checked with the chaps at the Royal Horticultural Society on this one. They say that applying Epsom salts (magnesium sulphate) seems far too easy a solution to the problem of this irritating fungal growth, which causes spreading concentric circles of dying grass to appear on the lawn. It was not a cure with which they were familiar.

Dealing with fairy rings can be a difficult and expensive job - as you are clearly aware. The only fungicides that are properly effective are not available to the public, so you would have to call in a professional company. Treatment does involve digging into the lawn to treat the soil underneath.

The more pragmatic approach would be to give the lawn regular high-nitrogen feeds to keep it verdant, so that the rings will be less noticeable.

Help with herbs

Jane Harrad-Roberts from Chester has inherited a neglected herb garden and is trying to get to grips with it. She needs a good book and/or a helpful website. I suggest Jekka's Complete Herb Book (Kyle Cathie, £12.99). Jekka McVicar is a Chelsea Gold medallist, a great herb enthusiast, and also has a website (www.jekkasherbfarm.com).

Camellia problems

M. Wadham from Strathaven is cross with a camellia, aged nine, that steadfastly refuses to flower, even though it has now been transferred from pot to ground. Patience, M. Wadham, patience. Besides being prima donnas when it comes to soil pH and root conditions (cool, acid, moist and leafy soil are de rigueur), camellias also take time to settle into their new surroundings.

Don't get so cross with your camellia that you deny it plenty of water this summer, when it will be making next year's flower buds. This is, I am told, one of the most common reasons camellias fail to flower - we forget about their needs when the rest of the garden gets all our attention.

If you have to use a lot of tap water, or if your soil is not particularly acid, give your camellia a tonic of sequestered iron in the form of Sequestrene (available from garden centres).

Mrs Locket from Cheshire is disappointed that the flowers of her white camellia seem to go brown all too soon. She wonders if she is doing something wrong. You are doing nothing wrong, I am afraid. They do that. The flowers of any camellia that performs early in the year will go brown if they catch the morning sun after a frosty night.

Green haze in the greenhouse

The water from my water butt seems to be causing a green haze to grow over the soil of the plant pots in my greenhouse. The problem does not arise if I use tap water. Is there a treatment that would correct it? John Wilson, Cumbria

Tap water is, of course, cleaned of "impurities". Rainwater - and tap water that is left standing - picks up spores of moss and algae that are in the air and will eventually turn green. When the spores come into contact with the nutrients in the soil of your pots, they start to grow - hence the green haze.

There are several products that control the formation of algae. I suggest you try ReFresh from Biotal, a biological treatment for slimes, smells and water-butt evils. It is available through garden centres at £6.99 for 500ml, which should be enough for about three months' treatment.

Sweet nothings

Philippa Gunn emailed to say that she wants to grow sweet potatoes. Unfortunately, our summers are not long enough - sweet potatoes are a tropical, trailing, tuberous relation of ipomoea (morning glory). One or two varieties will grow in southern Europe, but not here, I am afraid.

Write to Thorny Problems, Helenyemm1@aol.com or The Daily Telegraph Gardening, 1 Canada Square, London E14 5DT. Helen Yemm can answer letters only through this column. Helen Yemm will be speaking on The Daily Telegraph Stand (K56) at The Daily Telegraph House and Garden Fair on Friday, June 29 from 11.15am-12.15pm. She will also offer a consultation service from 12.30-1.30pm, 2-3pm and 3.30-4.30pm. The fair is at the National and Grand Halls at Olympia, June 28- July 1. Tickets cost £14, but Gardening readers pay £9 in advance. Ticket hotline 0870 121 2525, or www.houseandgardenfair.co.uk.

-- Anonymous, June 26, 2001