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Gardening: A twist in the plot

Gardener's workshop: Anna Pavord adds a purple patch to a potted garden
My son has just bought his first flat. It has a communal walkway facing south and a wooden trellis that separates him from his neighbour. The previous owners left him all their containers, mostly plastic, but the only surviving plant is a small-leaved ivy with silver variegation. His knowledge of gardening is nil and, when he found out the price of annual bedding plants, he asked me to suggest some shrubs and plants that will last for a couple of years, like the perennials we have in pots on our patio. The plants will be a present from us. Would small hebes such as 'Nicola's Blush' be happy in this situation? Since they are evergreens, he would then have something to look at during winter. Next autumn I could order some small bulbs - crocuses or the narcissus 'Tete- a-Tete' - and put them between the permanent plants to give colour in spring. But what compost should I use? Would you recommend fertiliser pellets? Don't suggest any tender plants. There is no space to bring anything inside for winter.

Well! I thought as I read this letter. Alicia Windibank is setting high standards of parenting here. I hope none of our children expect the same service. I can scarcely keep up with my own garden, let alone taking on one of theirs.

Mark Windibank (30) was abroad when I went with Mrs Windibank to his Blackheath flat, built, I would guess, at the same time as the vogueish Span developments of the Sixties. All the flats have big picture windows looking out on to the first-floor walkway that connects the row. Some of Mark's pots are grouped in shade under his window, some stand in a sunny row along the railings. Everybody else in the row makes a big thing of flowers in tubs. As Mrs Windibank pointed out, it would be unneighbourly if Mark did not do the same. Novice or not, he must have blooming pots.

The biggest of the containers was a wooden trough 9in wide and nearly 6ft long. This had possibilities. The rest of them (there were 19 in all) were too small to offer much opportunity of mixed plantings. My first piece of advice to Mark would be to throw away the eight 5-in pots hanging on the trellis and invest in one big tub instead. It will be much easier to look after. The compost in a big tub will not dry out as easily, and in a sunny situation the compost in a 5-in pot heats up to uncomfortable levels for plant roots struggling to stay cool and moist.

Five of the containers were plastic urns on pedestals, 9in deep and 12in wide. But walkways are windy places and pedestal containers are inherently less stable than pots with a heavy base. So when the urns crack up (as plastic pots inevitably do) I would replace these, too, with one or two much bigger and deeper containers.

A heavy John Innes loam-based compost would to some extent compensate for the potential instability of the plastic containers. Since Mark wants shrubs and perennials, he should use John Innes No 3. At 30, he should be able to lug it up on to the walkway without collapsing. That's the disadvantage of loam-based composts; even a small bag is astonishingly heavy. But it is nutritious.

If he used a loam-based compost, he would probably not need to include water-retaining granules. In a soilless compost, these would be invaluable in his small containers. As for food, he can choose. Fresh compost has enough food to sustain plants for at least six weeks. After that, he could either scatter a slow-release fertiliser (such as Osmacote pellets) on top of the compost, or use a liquid feed when he waters.

If the underpinning is right, then the plants will be happy. That is why Mark needs to think carefully about the containers and the compost. If he gets it wrong, then he'll waste more money on dying shrubs and perennials than he ever would on annuals.

And on the question of annuals, I still think a fiver spent in the Columbia Road Sunday market would do more to brighten up the walkway than any number of serviceable perennials or dwarf shrubs, but perhaps one day Mark will get round to thinking that himself. In the meantime it's his patch, not mine, and he must have what he wants. Except that I would beg him to invest in a few balcon geraniums to stand in the small trough on top of his dustbin hutch. It's right by the front door and a froth of blossom there from now until October will be the best investment he could make. Mrs Windibank might even volunteer to overwinter some cuttings for him, then nobody could claim that they were an extravagance.

She had already taken the big trough in hand and planted it up with the geranium 'Ballerina', an excellent choice, growing about 6in high and spreading to about 12in. The flowers are soft, greyish pink, with darker veins. They shouldn't be overwatered in winter, but if well fed in summer, they will produce flowers from spring all the way through to autumn. I would have tucked a few lobelias around them to hang over the front of the trough and provide a colour contrast, but being annuals, they wouldn't be popular with Mark.

What about the hebe 'Nicola's Blush' Mrs Windibank mentioned? Hebes were a popular choice in front of other flats on the walkway, and you could understand why. They have a long season of flowering (June to November) and they are evergreen. 'Nicola's Blush' has mid-green leaves and pale pink flowers, which fade to white as they age. It's reasonably dwarf, usually no more than 2ft high and wide. 'Amy' is another good one, with bronze foliage and blue flower spikes. They both need sun. One of the important pleasures of gardening - especially in cities - is the way that it marks out the seasons, so Mark might like to invest in a camellia (planted in ericaceous compost) to stand on the shady side of his terrace, and plant spring- and autumn-flowering clematises to climb his trellis. He could experiment with agapanthus for late summer and autumn, surrounded by clumps of dark-leaved ajuga, which would give the same container interest in spring, when the ajuga sprang up into flower. 'Catlin's Giant' is the showiest, but I am very fond also of the dark-leaved variety 'Burgundy Glow'. Lilies would give scent and, with care, will flourish in a container year after year. A few crocuses poked in among them will make a lily pot sing in spring too. I'd avoid roses, but would try a fuchsia, such as the relatively hardy 'Mrs Popple', well underplanted with white narcissus such as 'Thalia'.

Small-leaved hostas would enjoy the cooler side of the terrace, and violas, too, can be kept going for a long time in containers, if you are ruthless about cutting them down in August. But having equipped her son with all these delights, Mrs Windibank needs to do something else: set up a regular e-mail saying "Water plants tonight".