Holiday plants (such as azaleas, cyclamens, forced bulbs, topiaries, kalanchoe, poinsettias), cut greens and live wreaths and trees aren't really meant to live indoors forever. They do best in cooler, moist air outdoors, but they can be kept in good condition indoors for several weeks if we try to replicate their natural environments.
Place holiday plants in cooler spots in the home, away from heat sources like fireplaces and furnace vents. Provide bright, indirect light, but not direct sunlight. In winter, the angle of the sun's rays is lower on the southern horizon and shafts of sunlight are not deflected by overhanging eaves. Southern light will be strongest in the house and, unless the sunlight is filtered through shades or shutters, the rays and heat can dry out or scorch tender needles and leaves on holiday plants and greens.
Remove paper or foil wrappings and place the pot on a saucer or into a cachepot to prevent damage to furniture. If the pot doesn't have a drain hole, use a nail to poke several holes in the bottom of a plastic pot or re-pot into a pot with a drain hole. Empty the saucer or a decorative cachepot after every watering.
Different houseplants require differing levels of soil moisture and differing methods of watering. Kalanchoe (pronounced cal-AN-cho) and Christmas cacti (shlumbergera) need consistently moist but not soggy soil while in bloom. Cyclamen are susceptible to gray rot if the crown of the plant is kept wet; pour water around the cyclamen but not over the crown. Poinsettias die quickly if the soil is allowed to dry out completely. Phalenopsis or moth orchids draw their water from the damp orchid bark; a couple of tablespoons of water a week is usually sufficient to keep the bark moist. Use your trusty finger (the best tool for determining moisture levels) and water azaleas, rosemary and ivy topiaries, poinsettias and forced bulbs when the top of the soil is dry.
Daily misting will lower humidity levels, but make sure that any lights on live holiday plants and trees are UL-approved outdoor lights. Anti-transpirants help prevent moisture loss from leaves and needles. You can find anti-transpirants at most garden centers and well-stocked nurseries. Cloud Cover and Moisturin 5 are two brand names. Spray anti-transpirants outdoors before decorating the greenery.
Before you set your tree into the container, make a fresh cut on the trunk. Then fill the container with sweetened, not diet, clear soda like 7Up or Sprite and add a squeeze of fresh lemon juice. The sugar in the soda provides nutrients and the lemon acts as an anti-bacterial agent. This recipe also works well to keep cut flowers fresh longer.