What Do Plants Need?

Most building interiors are designed for efficiency and comfort. That means a fairly constant indoor environment without too many changes in light, temperature and humidity. Buildings are also designed to keep the weather out. Wind and rain don’t make people feel comfortable. And they don’t help business, either!

Plants, on the other hand, thrive in weather and changing seasons. Rain gives them water and wind removes dead tissue and old leaves. Many species require the seasonal variation in order to drive their own physiological changes.

Those plants that can cope indoors have their own particular needs for Light, Temperature, Water, Growing media, Plant Nutrients and Humidity. These determined where the plants can be used.

Light is probably the most important element needed for plants to survive. 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 make sure that your plants are able to cope with their surroundings.

Plants need water if they 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 the roots, which then regulate the uptake of water and nutrients, and anchor and support the plant. 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 plant’s roots 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. However, the roots also require oxygen, which means they require a supply of air to. That is why compost media with large numbers of air-filled pores are essential, and why water-logged soils cause plants to die.

Interior landscapers can use various growing media. These media all have their advantages and faults, so it takes a certain amount of expertise to work out which growing medium works best in different situations. The growing medium has many functions. It needs to anchor the plant's roots; act as a reservoir for water and nutrients; protect 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. However, they do need some nutrients to maintain health, colour and growth. Fertiliser can be added to the growing medium, where the plants then extract it. 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 fertiliser has a balanced ratio of these elements, plus essential micro-nutrients, or trace elements. How much to use is determined by the size of the display and the environmental conditions. Large plants and those in particularly bright areas generally need 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 temperature range. Luckily, you can select from hundreds of species and varieties from the tropics and sub-tropics. They’re all ideally suited to such year-round warmth.