Anna Pavord's A to Z of pests and problems: N is for neighbours, nettles and nutrient deficiency

Our green-fingered correspondent Anna Pavord continues her A-Z of horticultural pests and problems standing between you and your perfect garden

Neighbours

Neighbour disputes seem mostly to do with boundaries – atavistic in the extreme. If it's a case of his fence or yours, house deeds may sometimes provide the answer. But even if it's his fence and he's letting it drip into your garden, you can still suggest (nicely) that you'll sort it out for him. It's better than inwardly fuming. Now that the dreaded Leyland cypress seems to have lost favour (it happened when people saw just what cuckoos-in-the-nest those first-planted ones could be), there seem to be less reports of disputes about hedges.

In a survey carried out last summer, more than half those questioned said that they were annoyed by their neighbours' gardens. But some curious irritations were listed among the top 10 bugbears, which were litter, overgrown plants, broken garden furniture, out-of-control hedges, dead lawns, half-finished decking or paving, gardens that were completely paved-over, children's toys left permanently outside, Astroturf and mock Grecian statues.

Wow! If I had nothing more awful to complain about than a fake classical statue, I'd consider myself rather lucky.

Nettles

Some gardeners consider weeds in the garden to be a sign of moral degeneration, the horticultural equivalent of cockroaches behind the cooker, but there is usually a reason for weeds. Nettles, for instance, attract early aphids, food for the hungry ladybirds waiting for the three-star meals to come later in the season.

Nettles are also an important source of food for the caterpillars of peacock, red admiral and small tortoiseshell butterflies. And they can be turned into a liquid feed. To make, soak about a kilo of freshly cut nettles in a barrel of water. You can use the liquid straight from the barrel after a couple of weeks.

Noise

There is too much of the wrong sort of noise in gardens: strimmers, lawnmowers, chainsaws and (worst of all) shredders unequal to the task in hand and so taking three times as long to do the job as a more powerful machine. It surely would not be difficult to make machines quieter. But when I raised this point with a manufacturer, hef said there wasn't sufficient consumer pressure for them to make this a USP.

Occasionally you find out that one machine is quieter than another – it's why we use a four-stroke strimmer rather than a two-stroke one. And electric mowers are quieter than petrol-driven ones. But electric is only an option when there's not much lawn to cut. Perhaps the only way out is a pair of Bose Acoustic Noise Cancelling Headphones – I bought them as a defence against snorers on aeroplanes, but they may help against shredders, too.

North

The shade produced by a north-facing garden is too often assumed to be A Bad Thing. In truth, shady walls and fences can be clothed as elegantly as sunny ones, provided that the shade is caused by lack of sun, not lack of light. You may not get as colourful a display as on sunny walls but foliage will be excellent.

Chaenomeles and pyracantha are both excellent on a north wall. I like chaenomeles (japonica) spreadeagled on a wall, pinned flat and pruned fairly severely after flowering to eliminate twigs that try to push out forward. This makes it easier to grow other things in front. Pyracantha is also best when it gets some corrective training. Over the years I've trained the pyracantha on our north wall to make a shape like a window, the branches crossing at right angles to make 'panes' against the wall. It's slightly dotty, but it makes me smile. The blackbirds like it, too.

Because rain tends to come in from the south and the west, north-facing walls and fences act as barriers, preventing the ground under them from getting properly wetted. Remember, though, that north walls face winter's coldest and most drying winds. Evergreens suffer more than deciduous shrubs. Foliage loses moisture faster than the roots can take it up. Leaves turn brown and die. But, hey, it may never happen.

Nutrient deficiency

Deficiencies may be of nitrogen, phosphorus, potassium, magnesium, calcium, sulphur, iron, manganese, copper, zinc, boron, or molybdenum, the macro- and micronutrients on which healthy plant growth depends. Different deficiencies cause different symptoms.

Mineral deficiencies cause disorders, rather than diseases, but the end result is the same: a plant that isn't growing as well as it should. Sometimes the fault lies with the soil – a very limey soil may lock up trace elements (minerals) that the plant needs. Sulphur chips help, but slowly. Sometimes over-enthusiastic use of one type of fertiliser unbalances the soil or compost and makes it difficult for the plant to retrieve other nutrients that it needs. If you overdo potassium-rich feeds (such as tomato fertiliser) it cancels out the magnesium which the plant also needs.

The most common deficiency is of iron which causes chlorosis. You can correct this by watering in a chelated iron compound such as Sequestrene. Manganese deficiency is closely allied to iron deficiency, and shows up on acid-loving plants trying to adapt to over-alkaline soil. Leaves discolour. Chelated iron helps. In containers, use compost formulated for acid-loving plants.

Deficiency of phosphorus occurs where plants are growing on soil that is too acid for them. Leaves, typically of tomato, curl up at the edges, or may turn a purplish colour. Growth is weak. Use a fertiliser rich in phosphorus (that's the P in the typical NPK recipe).

Potassium deficiency is most likely to occur on light, sandy soils. Plants flower poorly. Tomatoes colour up in a blotchy way. Wood does not ripen sufficiently and so is more prone to frost damage. Correct the problem with a dressing of sulphate of potash in spring and autumn. But don't overdo it.