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Stress-free planting

Forget soil and watering cans. The right balance of nutrients will result in happier and healthier plants, both inside and out

Hydroponics - growing plants without the use of soil - is set for a bright future. Straightforward, peat-free, clean, convenient, easy to maintain, and suitable for both internal and external soft landscaping, it is the obvious choice for effective yet simple planting schemes.

Expertise in growing plants hydroponically has been increasing steadily for the past 30 years in Germany and the Netherlands. Now Project Suzy, at the Millennium Commission-funded facility Hydroponicum in Middlesbrough, is opening up the planting technique to the UK. Forget Charlie 'water-feature' Dimmock, the issue itself is about to become 'sexy'.

So how does it work? The fact is that plants do not actually need soil to grow. They only require water, nutrients and anchorage. Admittedly, they get the latter from soil or compost, but find an alternative way of supplying those things and plants will grow quite happily.

The most popular indoor hydroponic system uses expanded clay pebbles (aerated clay marbles - a bit like cat litter) as the soil substrate (see right), though you must make sure that you use a suitable type.

Some clay pebbles used in the building industry contain harmful quantities of dissolved salts.

The correct clay pebbles provide the plant roots with the ideal release mix of water and air so there is no danger of rotting roots or patches of soil that are too wet or dry. More importantly, you don't get any of those annoying little black flies that usually appear with any indoor soft landscaping.

Nutrients can be supplied through a slow-release fertiliser which will last up to four to six months. The appropriate amount of water is always available to the plant via the management system feed pipes, providing, of course, that whoever is responsible for maintaining the plants remembers to look at the water level indicator (see photo).

For larger systems, (hydroponics are ideal for either domestic or large commercial-scale applications) an automatic top-up system can be installed. Further up the hi-tech scale is automatic feeding and a pump to keep the water aerated so that no part of the root area gets stagnant. This is especially useful for large planting schemes.

Hydroponic plants tend to be more resistant to other pests and diseases because they are happy - with food and drink on tap in just the right amount. And as with humans, the happier a plant is, the less likely it is to call in sick.

However - and this is where good building design comes in - hydroponically grown plants still need the right amount of light, warmth, humidity and access to regularly refreshed air. Most indoor plants like the same conditions people do; enough natural light, satisfactory ventilation (but not draughts), and a temperature not too hot and not too cold (although some prefer it humid). There is usually a plant for every situation. If light is a limiting factor, have no fear; growlights can easily be installed.

The trend towards having atria in larger buildings is perfect for internal landscaping. Plants not only look better when grouped together but they seem to grow better in the increased humidity that company brings. This offers a great opportunity for architects and interior designers. Design in a seating area with a water feature, and you have the perfect place for people to gather and chat over a cappuccino, or just to moan about how awful the coffee machine coffee is. Either way, the ambience engenders a sense of well-being, not to mention - so they say - improved productivity.

Remember, though, that in most buildings the heating gets turned off at night and in the winter the temperature can drop significantly, leading to stress for the plants. A well-thought out choice of plant can get round this problem in the same way that a particular structural material can deal with a particular type of loading stress. For instance, cacti love a south-facing glazed location, where a rubber plant would scorch. They do not need water in the winter and most of them can cope with temperatures close to zero, so are ideal for erratic heating environments. Set in brushed stainless steel containers among crushed glass and cullet glass boulders in a minimalist plate glass entrance foyer, they look fantastic.

The recent rash of home makeover programmes has raised public expectations of something new, modern, different and stylish. Unfortunately for the architect, most clients do not really 'see' the building, they see the fittings and soft furnishings (an exception being Tate Modern, where the reverse is true). It is absolutely vital, therefore, to specify internal soft landscaping as an integral part of the building, and consider hydroponics.

The best approach is to get thelandscape designer in at the start of the process and go for a definitive statement. There is nothing more depressing than sad rubber plants and partially leaved weeping figs scattered randomly around a building in little plastic tubs.

Hydroponic growing also has great potential on roof gardens - something to remember for that next building in Tokyo. The same techniques apply, and there are added benefits to using hydroponics in an elevated external environment. With hydroponics it is easy to change the proportions of the nutrient feed to prevent plant leaves from growing too large and lush and more easily damaged by the wind. Peat-based compost can go sour after several years of growing plants and can easily be washed out in exposed conditions. Soil-based composts are generally too heavy, whereas expanded clay pebbles or cracked clay pebbles (which tend to be used outdoors) are inert, light and reusable for years.

It is worth dispelling the myth that hydroponic plants are somehow 'special' or 'different' to 'ordinary' plants.

In fact, the outdoor plants do not even have to be bought from specialist hydroponic sources. It is possible to plant straight from soil into the pebbles, a hybrid system referred to as terraponics. The new roots that the plants subsequently grow become adapted to the hydroponic system.

And because it is easy to ensure a constant water supply without saturating the roots, the plants do not become water stressed, a particular problem with windy and hot rooftop gardens.

Again, involve the landscape designer from the start of the process. Architects the world over always wish that the services' engineer had told them the exact route of the M&E services before the contractor fixed the beam in the middle of the duct run. In the same way, it is better to find out early that the extraction fans are pointing in the wrong way, preventing plants from growing. Also too often, lack of communication leads to significant rearrangements of a design layout.

If it's too late I suppose you could always fall back on plastic plants.

Martin Allen is a horticultural consultant working on the interior landscaping for the Project Suzy Hydroponicum in Middlesbrough.

Contact: 01642 5762950

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