Your first introduction to Norfolk Island pine may have been when you received a small plant trimmed with ribbon and miniature red ornaments as a Christmas gift. But while many Norfolk Island pines begin their lives as petite houseplants, they are capable of tremendous growth. Every year I get a call or two from someone whose plant has grown so successfully that it's nudging the ceiling.
While not among the easiest houseplants to grow, Norfolk Island pines grow well if you provide an agreeable environment for them -- just the right balance of bright light and lower temperatures.
The best way to ensure long-term success with these plants as indoor greenery is to learn how and where it grows in its native habitat.
Despite its name, the Norfolk Island pine is not a pine. And, though they're used as landscape plants in southern Florida and California, they are not native to North America. Instead, they belong to the Araucaria family, a group of tropical and sub-tropical "primitive" conifers indigenous to the southern hemisphere.
In that hemisphere, exposed to lots of sunlight and abundant moisture much of the year, these trees can grow well over 200 feet tall. And though they possess little or no frost tolerance, they easily tolerate lower temperatures -- the kind we sometimes have indoors.
Norfolk Island pines grow best in a bright, sunny location indoors. Too-intense sunlight can lead to a faded yellow-green appearance, however, so pull them back a foot or two from south or west windows in summer when light is strongest and most plentiful.
These plants can adapt to survive many years of lower light, but inevitably their form will suffer under less than optimal conditions. Plants stretch and become spindly; older branches take on an unattractive, droopy appearance, and there will be more stem space between one year's whorl of new branches and the next.
Norfolk Island pines typically put out one whorl or tier of new branches annually. If the plant isn't rotated regularly, it loses its symmetry and grows toward the light.
Two of the most common problems these plants face indoors are browning needles and drooping lower branches. This usually can be attributed to hot, dry air, low humidity or allowing the soil to dry excessively between waterings. Too much fertilizer also can contribute to needle drop and branch loss.
This time of year, ideal night temperatures for Norfolk Island pines range from 50 to 60 degrees, with daytime temperatures only about 5 degrees higher. Spring and summer temperatures may be higher, because there's plenty of light to support more active growth.
While you can lower your thermostat, it's practically impossible to regulate indoor humidity in a way that provides an ideal humid environment for Norfolk Island pines yet isn't too humid for people and household furnishings. You can compensate for lack of humidity by watering the plants carefully and conscientiously.
Keep the soil relatively moist, but not saturated, most of the year. Water the plant thoroughly, but spill or siphon off any excess moisture left in the container's tray after a few minutes. Check the soil every few days, and water thoroughly again once the surface feels dry. In winter, when temperatures are usually lower indoors and there are fewer hours of daylight, allow the soil to become a bit drier -- but never bone dry -- between waterings.
Because Norfolk Island pines are slow-growing, they need repotting only every three to five years. Use fresh potting soil that drains well, yet contains a reasonable amount of organic matter in the form of peat moss, and choose a pot that's not much larger than the old one. Keeping the plant's root system a bit confined may help maintain the tree at a smaller and more manageable size for a longer time.
During spring, summer and early autumn, fertilize Norfolk Island pines with a dilute houseplant fertilizer every few weeks. Use a product meant especially for acid-loving plants, mixed half-strength. You shouldn't have to fertilize new plants, purchased for the holidays, until late February or early March.
And what about those callers whose plants have hit the ceiling? There are only two choices; give the plants away -- or move to another house! You can't prune a Norfolk Island pine without deforming it permanently.
-- Deborah Brown is a horticulturist with the University of Minnesota Extension Service Yard and Garden Line. For help with garden, plant and insect questions, call that service at 624-4771 in the Twin Cities metro area.