4. Maximum moisture
The air in the average home in winter holds about as much moisture as the Sahara Desert. That might be okay for cacti from arid regions. But many foliage and flowering potted plants originated in equatorial rain forests; they therefore want high humidity.
Clustering plants together will raise the relative humidity in their neighborhood. Consider adding a humidifier to the room or — with forced-air heat — a whole-house humidifier (for you and your plants).
An easy way to add moisture to the air is to place pots on trays filled with pebbles. When I water the plants, I water the trays as well. The pebbles increase the surface area from which moisture can evaporate, and they keep the pots from sitting directly in water.
5. Going to pots
If a plant is drying out faster than it used to, or if roots are poking out of the drainage hole, it might be time to repot. Move the plant to a container one size larger — from a 4-inch pot to a 5-inch one, for example. A pot that's too big (overpotting ) can yield soil that stays too wet, resulting in root rot.
Plants like to live in porous terra-cotta clay pots, which allow oxygen to reach the roots. But clay pots and the medium within them dry out faster than plastic or glazed ceramic ones. If you're frequently away from home, go with plastic. A variety of handsome plastic pots are on the market now, even biodegradable ones.
Containers must have drainage holes. If you want a decorative jardiniere that does not have a hole, plant in a plastic pot first; then slip that into the fancy container. Put some marbles or gravel and perhaps some aquarium charcoal in the bottom of the outer pot: This elevates the inner plastic container in case water collects in its bottom.
6. Diet time
Houseplants need to eat, but in the dead of winter, when they are not actively growing, I put mine on a diet and curtail feeding from as early as September until February, when new growth starts to appear. When I do feed them, I always halve the manufacturer's recommended rate.
Regarding plant foods: Every container of fertilizer — organic or not — will give three numbers in a ratio, for nitrogen (N), phosphorus (P), and potassium (K). Leafy foliage plants want N to be the highest number. Flowering plants want more P. Potassium (K) encourages root growth and general health. Choose different plant foods for different plants, or select a balanced product with equal amounts of the three elements.