It's clear that the days of trying to re-create a natural look in a city garden are long gone. When you think of it rationally, it makes sense. The terms of reference in an urban environment are more likely to be some kind of building material: brick, glass, wood, concrete, steel and so on, rather than the rolling hills or stands of native trees you would expect to find in the English countryside.
Less often means more when it comes to planting. Overly soft-looking gardens, especially if they are on a roof terrace, can feel out of place when surrounded by houses. To earn their keep, city gardens have to be multi-functional: somewhere to relax, to entertain, let the children play. But they should also provide a calming retreat, a place to go to escape from work and the many stresses of city life.
So a good balance between soft and hard landscaping in a garden is crucial to the overall feel. It is easy to imagine a completely "soft" garden - one that eschews hard areas altogether and depends entirely on plants and lawn areas. Conversely, it shouldn't be impossible to design a successful garden that is entirely plant-free. Don't get me wrong - I'm a big plant lover, but I have to admit that a classy bit of well-executed hard landscaping can also get my blood flowing.
Geometric shapes and clean lines work really well in city gardens. If the lines appear too harsh they can be softened with planting or pots. A layout with good proportions and a strong structure will come into its own in the winter months when a lot of deciduous or perennial planting has died back. I know amoebic shapes are tempting, but don't be seduced: in a city garden, they should be avoided.
Garden building can be split into two basic groups: horizontals and verticals. Horizontals are the surfaces - terraces, pathways and gravel areas; verticals are made up of the divides - walls, fences, trellis, pergolas. Elements in each group should be hard-wearing and practical but, to me, it is the way that they are put together that is important. Simplicity always works best. To get a clean, contemporary look, limit yourself to no more than two different paving surfaces. As a general rule, the unit size of the material should be proportional to the size of the garden.
For example, in a small garden use a small-unit paving material such as slate tile, granite sett or brick. Use larger paving slabs for larger areas. Reclaimed natural stone and bricks can be expensive, but they will give you a permanent "been there for ever" kind of feel. Newer materials will mean a newer-looking, possibly cheaper garden. Use them confidently to tie the garden to the interior spaces in the house.
If you want up-to-the-minute good looks that will outlast fashion, go for timber decking. I often get asked whether this is just a passing fad, but decking has been around a long time and can be seen as a classic rather than a trend. Decks have several advantages: they are quiet underfoot and give the garden a warm feel; they can be built quickly, so make a great DIY project (which, as a nation we find hard to resist) and, vital in a city garden where space is at a premium, they can cover a multitude of sins. Decks free-drain - important if you're planning to change existing levels in your garden. If you can't afford hardwood decking, go for tanalised (pressure-treated) softwood. It's approximately one-third of the price of hardwood and, if maintained properly, will last 15 to 20 years - more than long enough for most of us.
When it comes to walls, a smooth-rendered cement finish will give you a good clean look - particularly appropriate for a retaining wall around a raised bed. By painting it in different shades, cement also provides plenty of opportunities to bring some real colour into a garden. If you're stuck with an ugly existing wall, transform it with cladding: zinc sheeting, for example, or split bamboo. As a space-saving factor, consider in-built seating when putting in walls. The inviting sight of somewhere to sit in a garden can subtly draw you into a space that you have previously ignored.
Pergolas and arches provide many opportunities for creative thinking. What about using copper piping, canvas (for shade) or stretched yachting cable - it's the way these materials are used that will make all the difference.
Speaking from long experience, the search for genuinely interesting, original "garden features" at your local garden centre is frustrating and unrewarding. And, in any case, do you really need them? For my money, a well-designed set of steps or a custom-made trellis will do far more to make your garden interesting and personal than any number of ersatz "features".