Winter days are short and, in many areas, cloudy. Even on a sunny January day, plants may get less light than they need and will live on the reserves of photosynthetic energy they've stored up over the summer. Some plants—such as philodendrons, Chinese evergreens (Aglaonema cvs.) and dracaenas—can live for months on these reserves but others show telltale signs of weak, leggy growth, or experience leaf loss or even death if they don't recharge daily.
The most obvious solution is to move plants to a brighter location. Big windows let in more light than small ones, and plants placed close to (but not touching) glass will also get more light. The sunny, south-facing window that was too hot for plants in summer can be a haven for them in winter. Rooms with light coming from two or more directions are a godsend, as are, of course, the ultimate houseplant winter havens: solariums and greenhouses. Be wary of north-facing windows, basement windows or any location far from a window. Although they may seem bright enough, they can rarely support much plant growth in winter.
Try using pale colours when decorating around plants. Pale colours reflect light, which plants can use. Forget plum walls and mahogany furniture: they absorb light.
If you don't have enough sunny windows or the budget or inclination to indulge your plants with new decor, there's always artificial light. For example, fluorescent lights are inexpensive to buy and run, give off lots of light in an acceptable spectrum (which means mostly blue and red light waves) and don't burn plant leaves unless the leaves touch the tubes. A simple, two-tube lamp using 120-centimetre, 40-watt tubes suspended 15 to 30 centimetres above the plants will keep most of them happy. You don't need special horticultural tubes; a pairing of one ordinary cool white with one warm white fluorescent tube per fixture will do the job nicely. For plants that need lots of light, such as miniature roses, some orchids and most cacti, use a four-tube fixture. Fluorescent lights can even be hidden from view inside bookshelves, in the basement, in the attic, under stairs or in a closet—I have a light garden in an unused fireplace.
Any artificial lighting for plants should be on a timer: 14- to 16-hour days will convince most plants it's still summer, stimulating healthy growth and abundant flowering. Exceptions are plants such as poinsettias and Christmas cacti, which will grow but not bloom under long days of light. Give them their own lights and set the timer for 10 hours; then watch them bloom their little hearts out.
Photo: An unnamed Phalaenopsis orchid cultivar. Photography by Anne Gordon.