Turns out Aunt Edna was right: indoor plants are good for your health. Their mere presence can lower your blood pressure (no, really), and even improve your productivity (which is probably great news for bosses – see Houseplants Make You Smarter in Scientific American: “Recent research suggests that the mere presence of plants can boost your attention span”). And of course we all know that they really do relax you – just because they’re there.
But what’s good for the health of the plants?
Besides a regular feeding schedule and an appropriate watering regime (overwatering being probably the biggest killer of our leafy friends), plants need the right kind of light if they’re to survive and thrive.
It might seem counter-intuitive, but photosynthesis (the process in which the energy from light is turned into the chemical energy that fuels growth) relies on light from the visible spectrum, and not on ultraviolet or infra-red light – which provide either too much or too little energy for most biological systems.
The sweet spot for most indoor plants lies in the blue spectrum – although the irony for the homeowner is that you can’t just look at the light coming from a globe to tell whether it’ll bring enough blue into the room.
Don’t always look north for light
The other counter-intuitive thing about indoor plants is that skylights and north-facing windows might not be best for them: although they let the sunlight in, they usually filter out the blue light in the process (which is why sitting behind a sunny window in winter is so snuggly – it’s the infra-red light that’s warming you).
Colour temperature is measured in kelvin – lower numbers for red, and higher for blue – and grow lights range from 2 200 to 6 000 kelvin. And although you can get away with germinating seeds under stock-standard incandescent lights, you’ll want specially-designed grow lamps if you’re thinking of installing a serious indoor garden.
Grant Ballack – owner of Finishing Touch Lighting Design House – supplied the lighting for the massive indoor plant wall that forms a dramatic centerpiece for the triple-volume lobby of Knysna’s 5-star Simola Hotel and Spa.
“Standard low-voltage globes are generally quite good for plant growth since they’re as close to daylight as you can get – but special situations demand specialist lighting,” he said.
Plant lamps come in varieties – fluorescent lamps, HID lamps (which include sodium lamps, metal halide lamps, and mercury vapour lamps), and even LEDs – but the designers chose to install Plant Grow lamps (R63 spotlight globes) at Simola because, said Grant, they provide the optimum spectrum for the ferns, orchids, and other exotics that the horticulturists have planted there.
“For the homeowner, the choices can be quite bewildering, so it’s always a good idea to seek advice when you’re designing your indoor garden,” he said. “Your lighting designer will need to know how large the planted area is going to be, how far the plants will be from the lamps, and a number of other facts before he or she will be able to guide you to the right lamps for your needs.”
He warned, though, that grow lamps are often – to use the nurseryman’s phrase – heavy feeders.
“The data on LED grow lamps is still inconclusive, and all the others usually demand 60 to 80 watts of power -– so you’ll have to factor that into your maintenance costs after installation,” he said. But the results will be worthwhile – especially since (as we’ve seen) your indoor garden will surely offset the stress of the cost of owning it ...