What Do Plants Need?

Most building interiors are designed for efficiency and for the comfort of the people that use them. That means a fairly constant indoor environment without too many fluctuations in light, temperature and humidity. Buildings are also designed to keep the weather out. Wind and rain aren't comfortable and they aren’t conducive to good business, either.

Plants, on the other hand, thrive in the full face of the weather and changing seasons. Rain is the main source of water and a strong breeze does wonders because it removes dead tissue and old leaves. Many species even need seasonal variation to trigger changes in their physiology.

Those plants that are adaptable enough to cope indoors have their own particular requirements for Light, Temperature, Water, Growing media, Plant Nutrients and Humidity all of which which dictate where they can be used.

Of all the elements required for plants to survive, light is perhaps the most important. Without it, plants die very quickly. But how do you know which plants will survive in the different light levels that are found in a building? Some species may only thrive in a well-lit atrium, whereas others might be able to cope with the low light found in a seldom-used conference room. Accurate light measurement and expert species selection will help to ensure that you will get the look you require.

Water is essential if indoor plant displays are to survive for more than a week or two. Indoor plants need just enough water to maintain their physiological wellbeing, but no more. Water enters the plant by its roots, highly specialised organs that regulate the uptake of water and nutrients, as well as provide anchorage and physical support. Unless the plant is an epiphyte (a specialised group of plants that live among the tree tops, e.g. bromeliads and many orchids) or a water plant, the roots of a plant are buried in the soil. This is where the water needs to be and that is why professional interior landscapers use subterranean irrigation systems to deliver water directly to the rooting zone. Roots need oxygen to work properly, so a supply of air is also necessary. That is why compost media with large numbers of air-filled pores are essential, and why water-logged soils cause plants to die.

A wide variety of growing media are used by interior landscapers. They all have their advantages and faults and it is quite a complex science to work out which growing medium works best in different situations. The growing medium has many functions. It must provide a suitable anchorage for the plant's roots; act as a reservoir for water and nutrients; be a buffer against sudden changes in the environment (especially changes in temperature). And, for indoor plants in containers, it must be heavy enough to provide stability and reduce the risk of the plant display toppling over.

Most of the water given to plants is used for transporting soluble nutrients around the plant. It eventually exits the plant through pores (stomata) on the surface of the leaves through a process called transpiration, a process that varies with humidity, light levels and temperature.

Interior plants are not usually heavy feeders although nutrients are needed to maintain health, colour and growth. Fertilizer is usually applied to the growing medium, where it can be extracted by the plant roots. The three most important plant nutrients are:

• Nitrogen (N), for healthy green leaves and stems
• Phosphorous (P), for healthy root growth
• Potassium (K), for better flowering and colour

A good fertilizer will contain a balanced ratio of these elements, plus essential micro-nutrients, or trace elements. Fertilizer use depends on the size of the display and the environmental conditions. Large plants and those in particularly bright areas generally require more nutrients than small plants and those under poor growing conditions.

The temperature inside most occupied buildings usually falls between 16 °C and 25 °C. This is comfortable enough for most people. So, if you want plants in your building, you need to find those that can survive well at the same temperatures. Luckily, there are hundreds of species and varieties from the tropics and sub-tropics to choose from. All ideally suited to such year-round warmth.