The best time to repot houseplants is in spring when the plants are actively growing. If you are "shifting up" to a larger pot size, remember to move up just one pot size larger (usually 2 inches, such as from 4" to 6"). Houseplants, in general, like snug quarters; you do not need to give them too much space. If the pot is too large, the roots of the plant will not fill up the container. In this case, the soil stays damp for a long period of time, and plants are more susceptible to root rot.
If your plant is in flower, wait until it finishes flowering before you repot. Some houseplants, for example orchids, need to be repotted every 1 to 3 years to add fresh potting medium because the fir bark chips break down and lose their porosity.
Some houseplants are so large that repotting is difficult. With a spoon, carefully remove 1 to 2" of potting soil from the surface and replace it with fresh soil. But if the plant is a manageable size, place the pot on its side and knock the plant out.
Artificial light works well for most houseplants. Traditionally, homeowners use two fluorescent tubes, one warm white and the other cool white. Full-spectrum lights are also available, although they tend to be expensive. The intensity of the light is greater in the center, so many growers prefer 48" tubes for best results. Replace your lights once a year before they burn out. Don't use regular, incandescent bulbs;they are less energy-efficient and too hot for most plants.
Place flowering plants 6 to 12" beneath fluorescent lights and foliage plants 12 to 24". Plants generally do best with 10 to 12 hours of light a day, which can be regulated with a timer. Plants under artificial lights tend to need more water and regular feeding. Placing plants on a pebble tray using pea gravel, aquarium gravel or white quartz chips is a good way to keep humidity levels high and catch runoff water.
Generally speaking, foliage plants tend to need bright light but do not require direct sunlight. Variegated plants tend to need more light than non-variegated plants. Flowering plants, cacti and other succulents need some direct sunlight.
One easy trick for increasing humidity around a plant is double potting. Keep your houseplant in a plastic pot (always with drainage holes), and place it in a larger decorative pot (which does not require drainage holes but can have them). Soak either sphagnum moss or peat moss in warm water and squeeze most of the water out. Pack the filler between the pots and keep it moist (not wet). If you are using peat moss and it dries out, you will need to remove it from the pot and re-soak it until hydrated.
You can also use pebble trays to increase the humidity around your plants. Fill a tray with 1 to 2" of pebbles (or gravel). Then fill the tray with water and set your plants on top of the pebbles. As the water in the tray evaporates it increases the humidity level. However, always make sure the pots are not sitting in water. When you fill the tray be sure the water level is below the top of the pebbles.
Yes. Your plants need to breathe. Dust also blocks sunlight and reduces the amount of light reaching the plant. If you let them sit in your house and collect dust, they will start to suffer. You will also weaken the plant, rendering it prone to insect attack and disease. The easiest remedy is to take a damp cloth and gently wipe it off the leaves. More effective is to take the plant into the shower and rinse it off. Make sure the water is tepid and the pressure is not too strong.
It is important to clean your pots before reusing them, to get rid of fertilizer salts and diseases. The age-old recipe is to soak pots in 1 part bleach to 9 parts water for 15 to 30 minutes. Scrub pots with and old scrub brush and rinse. If your pot is covered with crusty depots of fertilizer salts, try mixing 1 part vinegar to 1 part water and scrubbing the pot with steel wool before you clean it.
You can grow healthy houseplants by remembering a few simple rules:
Sticky sap may be a sign of insect problems. Aphids, mealybugs, scales and whiteflies all exude a honeydew or sticky substance on the leaves. Search the plants for other signs of insects.
The best way to get rid of these pests is to spray on a mixture of soapy water. There are many recipes available and garden centers also sell ready-made insecticidal soaps. Always use mild soap and test the mixture on your plants before applying. If the soap is too strong, it will strip off the nice, shiny cuticle layer of your plant and could damage the foliage.
Two other popular home remedies are rubbing alcohol (1 part alcohol to 9 parts water) and Murphy's Oil Soap® (2 tbsp. soap to 1 qt. water). Remember not to apply these remedies full-strength or you will burn the leaves. Always dilute them or apply directly to the problem area by taking a cotton swab and wiping off the pests.