Anna Pavord's A to Z of pests and problems: T and U are for theft, thrip and unintelligible instructions

Frost-protected plants wrapped in fleece (Alamy)

Tender

You can't blame a plant for being tender. The problem lies with us gardeners, who are not content with growing stuff that has evolved naturally to cope with our unpredictable weather. A run of mild winters, combined with a fashion for bananas, cannas and other tropical-looking gear, made us slap-happy about the effects of frost.

For years, temperatures, particularly in city plots, rarely dipped below freezing. But recently we've had a run of tougher winters and we need to take notice of the new hardiness ratings established for all plants by the Royal Horticultural Society. These range from H1a (tropical plants that need to spend their entire lives under glass at a temperature of around 15C) to H7, the rating given to the hardiest plants, able to cope with winter temperatures of -20C. Plants given H4 rating will survive the average British winter, in temperatures between -10C and -5C. Check before you buy.

Theft

High-level garden theft hit the headlines when firms such as Sotheby's in Billingshurst began to develop a specialist market in antique garden statuary, seats and urns. Victorian cast-iron twig and vine benches which had mouldered for years under dripping summer trees suddenly acquired astonishing value. I first wrote about this new phenomenon in the Nineties. Sadly, although it's no longer new, it's still with us. As always, the thieves manage to stay a step ahead of the increasingly sophisticated alarms and marking systems that owners are forced to employ to hang on to their cherubs and quietly mossed-over lions.

As I reported before, the National Trust, in whose gardens is a remarkable collection of antique urns, statues and furniture, has been the victim of some particularly damaging thefts. At Wallington in Northumberland, thieves were disturbed as they were trying to remove the fine lead statues which decorate the walled garden. The tenant of the portico house in the garden fortunately discovered the perpetrators when he returned home late at night.

Police put thefts from gardens in the same category as burglaries from houses, so you can't put an exact figure on how much is stolen from gardens. Latest Home Office figures suggest that five thousand gardens are targeted by thieves every week. Most commonly stolen are garden plants (nearly a quarter of those who suffer from garden theft lose trees and shrubs, sometimes whole hedges).

Tools are popular with thieves, but many gardeners now etch or paint a postcode on expensive items. That makes them much more difficult for thieves to sell on. But the stolen lawnmowers, strimmers, generators, garden tractors and power tools I wrote about originally are still favourite targets. Keep a record of the serial numbers; if your nicked chainsaw gets found, it's the easiest way to prove you are the rightful owner. Use gravel for your garden paths. The inevitable scrunch is as good as a shed alarm.

Rare plants were stolen from Ventnor garden (Alamy)

Stealing lawnmowers and strimmers can be seen as the outdoor equivalent of lifting televisions and DVD players from inside houses. Reprehensible, but comprehensible. What is more surreal is the way that an entire pond, together with fountain and fish, can disappear > in a night, as happened to a gardener near Crewe in Cheshire. But all those who love gardening wince more painfully at news of plants being stolen than they do when told of purloined lawnmowers or strimmers. As well as being animate, plants are personal, in a way that a ride-on mower can never be.

So it's particularly shocking when entire collections of rare plants are stolen. Some time ago, it happened at the botanic garden at Ventnor, Isle of Wight, where, over 17 years, the curator, Simon Goodenough, had built up a fine collection of pseudopanax, strange spiky plants originating in New Zealand.

There's a worrying increase, too, in the theft of dogs from gardens – running now at 135,000 a year. Top of the list are springer spaniels, border terriers, and boxers. Dog thieves have evidently got good taste. But it's a mystery how a dog thief can ever persuade a springer to go off in the right direction when their owners so rarely can.

Insurance companies, always quick to spot an opening, are now offering specialised garden insurance to home owners. Policies vary in their comprehensiveness. Some cover plants in conservatories and greenhouses, but not those growing outside. Some cover hedges but not individual shrubs and trees. Check your policy. Full cover for plants may be available. But for an additional premium of course. Some companies offer substantially reduced insurance premiums if a house and garden are not left unoccupied for long periods. Some home contents policies will only cover garden machinery if it is kept under lock and key.

'Thieves', though, come in many guises. I've written before about the trio of oldish ladies who were creating havoc in the gardens they visited, hiding plants and cuttings in a selection of large handbags. The oldest (aged 80) was the mother of the other two women. They said it was all her idea. The cartoonist Giles's Grandma is evidently alive and well and living in Northumberland.

Thrip

Thrips feed on the sap of plants, like aphids. If you see leaves mottled over with fine, silvery-white lines, they might well be the cause. Different types of thrip attack onions, gladiolus, peas, privet and a wide range of indoor plants such as streptocarpus and African violet. Like aphids they can transmit viruses from one plant to another. On indoor plants and in greenhouses that are kept above freezing point, they can breed all year round. Yellow sticky traps will help to control their numbers.

U is for...

Unintelligible

This applies to the instructions on any knock-down, DIY piece of equipment which has 'Assembled in five minutes' plastered on its packing. Beware. Instructions are always written by people who have done the job a zillion times before and cannot comprehend the panic that overwhelms a first-timer confronted with seven pieces of tubing, three bolts and a lost wing nut, all supposed to transmute into a gazebo. Stay simple. Avoid equipment that tells you it packs away flat after use. Unless it is there, up and running, you will not use it at all.