Thorny problems: how can I get rid of lichen? Lavished with lichen Please can you advise a way of eradicating the orange lichen which has coated many of my mature and large shrubs, inhibiting growth of new shoots and weakening them? I have read that the plants need feeding and that is the reason the lichen has taken over, but they are fed and cared for and the garden has an open aspect. My research suggests there is no cure apart from scraping off the lichen, but that would be impossible. Could I scrub it off with a garden cleaner before the plants come into leaf? Angela Moss, via email Perhaps I can untangle a couple of frequently crossed wires here. First, lichens, close relations of moss and algae, are spread by airborne spores. In general the cleaner the air, the more likely it is that lichens of all kinds will become established on stone, roof slates and tiles, wooden garden structures and slow-growing living woody plants. This includes the bright orange dusty-looking lichen you mention, as well as various yellow and greyish crusty and mossy-looking growths, The lichen on your mature trees and shrubs is not weakening them or even inhibiting new growth, but its presence is an indication that they are growing very slowly. This may be simply down to their age, but if you are really concerned to kick-start some new growth that will outstrip the lichen, then clear away any invasive undergrowth around the base of each plant, give each a fistful or two of a balanced general fertiliser (blood, fish and bone) in spring, mulch them and prune annually at the appropriate time. So please stop worrying, and certainly don't get out a bottle of gunk and the scrubbing brush. Let Mother Nature have the upper hand, in this case. Oranges... and lemons Kate Vernon sent me a picture of her 10-year-old orange tree. It has had a good life, spending winter in her sun lounge and the rest of the year outside. It rewards her by producing small oranges all year round. But this is an orange tree with a difference. Imagine her surprise when she noticed a small crop of lemons maturing on one of its lower branches. What has caused this, she asks? It is all about grafting. The ornamental orange must have been grafted onto the root of a more vigorous lemon, and the branch that carries the lemons has come from a bud growing from that root. This sort of thing happens a lot with roses that are grafted on to wild rose rootstock, of course, but I had not seen it on a citrus bush before. As with the roses, the lemon may turn out to more vigorous than the orange. However, if I were Kate I would do nothing, revel in the curiosity factor, and just see what happens. Last month should have been declared National Daphne Month, to judge by the contents of my post-holiday in-box. Since I try to be conscientious about readers' most frequent freak-outs and foibles, I make no apology for returning to the subject (the last time for the foreseeable future). I am determined that matters daphne will not limp interminably into 2013 in the way that dying bay trees did in 2012. Farewell till next year, Daphne Doreen Woods from Hertfordshire has a magnificent, somewhat prostrate, Daphne tangutica that is doing so well it is now slumping all over her lawn. Given that she has an unheated greenhouse she can use, how and when should she try to take cuttings from it so that it can eventually be replaced? Daphnes are extremely slow-growing and are generally regarded as hard to propagate. But Doreen should certainly give it a try. Prepare now by cutting back a few branches of the old plant by a few inches, to encourage it to make new shoots from which to take cuttings later on. The time to do the deed is late summer, and Doreen should take several short heel cuttings, a few inches long, removing all but the top leaves before dipping them in hormone rooting powder, then poking them into free-draining cuttings compost. Moisture is crucial for the first few months. The unheated greenhouse may be a bit too hot and dry in late summer, so a sheltered spot out of the sun in the garden might be better. Also - nothing ventured nothing gained - since her existing plant is somewhat prostrate, she could also try a technique called "layering." This involves inducing a shoot or shoots that are touching the ground to produce roots, by carefully nicking a few stems close to a leaf and pegging them down to the ground. "Garden envy" can eat away at us. Dot Spillings's neighbour has a vigorous young (and new, judging by the photograph) Daphne odora, while her own 13-year-old plant has recently become, for want of a better description, threadbare, with small yellowing lower leaves and not much in the way of new growth or flowers. Both are growing in south-facing gardens, so why is her plant so shabby? New, tunnel-grown much-nurtured plants always look lush. Dot's plant looks old and starved to me and may, after 13 years have simply run out of steam. Maybe Dot should be taking cuttings (from her neighbour's plant?) too. Daphne Scofield's Daphne odora, which has this winter suddenly for the first time got brown tips to its leaves, probably suffered from frost damage after she knocked the snow off its branches. Unless branches of tender-ish evergreens become so laden with snow that they are in danger of splitting under its weight, it is best to leave them covered with the stuff rather than expose them to icy winds. Yet another Daphne, Daphne Gilham from Taunton, wants to know if there is a summer flowering/fragrant variety. Daphne transatlantica 'Eternal Fragrance' is the one - flowering from spring for most of the summer. You can find it in the Telegraph Garden shop. Or she can look up the plant in the Plant Finder section of the RHS website, where she will find a list of mail order stockists. Write to Thorny Problems at helen.yemm@telegraph.co.uk or Gardening, The Daily Telegraph, 111 Buckingham Palace Road, London SW1W 0DT. Helen Yemm can answer questions only through this column