Sniff it first, then shake it

It can be a bit like Battersea Dogs' Home, going to a garden centre; all those poor specimens just waiting for a bit of care and a decent home so they can flourish again. The main problem is exercising the discipline to walk quietly away with perhaps just one, instead of pressing the lot to your bosom and rushing home to ply them with bone-meal.

On the other hand, what are the pitfalls of walking into an establishment where the plants all look incredibly chirpy, with leaves shiny enough to shave in? How many of them will go to loving homes only to show signs of distress within hours of planting? If they are planted properly, with well-prepared and sufficiently large holes, and provided with water and a long-term source of nutrients, there is no reason for the buyer to feel guilty if the plant goes into a terminal sulk. It pays to look beyond the apparent health and vigour of the plant at the less immediately visible clues to its likely future performance.

Some people can look (and sniff) at the compost the plant is growing in and identify the country - even nursery - of origin with astonishing accuracy. It's as fascinating as watching Jilly and Oz on the Food and Drink programme (hmm, it's Dutch, Boskoop...the Van Oss nursery?) addressing an anonymous bottle of wine. However, all the canny plant buyer needs to be able to identify is whether the compost is loam-based or not. If it is, the plant has had a good start in life and is well set up for the future.

Much less encouraging - although far more prevalent - are plants grown in peat or its alternatives. Loam compost is naturally supplied with nutrients; it is easier to rehydrate, and it will be far more like the soil in your garden than, say, coco-husks, making the transfer from pot to border altogether more agreeable for the plant. Healthy-looking plants will no doubt have been "topped up" with liquid feed or slow release granules of, for example, Osmacote, but as this kind of treatment would ideally be continued at home, that's all to the good.

Soil-less composts, however, are devoid of any naturally occurring nutrients and get pumped full of them in the nurseries to ensure that their short shelf-life at the garden centre is as attractive to the customer as possible. As the spring season approaches, tens of thousands of perennials come over to our plant centres from the polytunnels of Holland and Belgium looking bouncingly fit. Look at the same specimens a couple of months later. You wouldn't want to buy them.

The most important indicator of the plant's eventual health is invisible to the buyer. The roots will tell you far more about a plant's future than its leaves or flowers. You should not be embarrassed to gently tap the plant out of its pot and examine the roots closely. No one would be the slightest bit surprised if you lifted the bonnet of a car you were thinking of buying. If the compost falls away rapidly to expose bare roots, then you know the plant has just been potted on. No container-grown plant should be placed for sale with its rootball unestablished. Bare- rooted roses are often given this kind of treatment at the start of the season; you will notice that the compost is suspiciously weed free and that stems chafe the edge of the pot.

Plants that cannot be tapped out of their pots because their roots have become so dense around the holes at the base are sad sights indeed. Matted, spiralling roots seeking an exit require patient, teasing fingers to enable them to find their way again. Perhaps they are best left alone.

Trees and shrubs are often too heavy to lift out of their pots for inspection. Buying them bare rooted in winter gives a clearer indication of the care the plant has received while in the ground. A fibrous rootball (as opposed to two or three large, severed roots) indicates that the tree has been regularly lifted and replanted. Avoid the problem altogether: buy very young trees or shrubs and treat them well at home. Much better than buying larger plants which will take years to overcome the upheaval.