Light, water, temperature, relative humidity, ventilation, nutrition and soil are factors that affect how well houseplants grow. You must also select plants that can withstand the indoor conditions of your home. There are many books and online resources available on houseplants and their care that can assist in your selection.
Light is essential for houseplant growth. Three important variables are intensity, quality and duration: the brightness of the light; the color of light, whether sunlight or artificial; and how much light the plants get in a 24-hour period, which is especially important for flowering plants. Southern exposures receive the most light, followed by eastern, western and finally northern exposures.
Too much or too little water can kill your plants. Don’t let the soil dry out completely between watering or let the plant stand in water for an extended period. A good way to check is to stick your finger 1-2 inches deep. If it’s dry, you need to water.
Foliage plants grow best in temperatures between 70 and 80 degrees during the day and 60 to 68 degrees at night. Indoor flowering plants like the same daytime temperatures but grow best with nighttime temps of 55 to 60 degrees.
You can increase the relative humidity of your plants by placing gravel trays under the pots or containers. Grouping plants together can also increase humidity. Houseplants are sensitive to cold drafts and heat from registers, so don’t place them near vents. Spraying mist on plants does not significantly affect humidity.
Houseplants need fertilization with three nutrient elements: nitrogen (N), phosphorus (P) and potassium (K). Fertilizers are sold as slow-release pellets that are placed on the soil or into the soil, as liquids, or as granules, crystals or tablets that are mixed with water for application. Make sure you follow the directions and refer to fertilization requirements for your particular plant.
It’s better to buy a commercially prepared potting soil than to buy ingredients and make your own. Mixes high in bark, forest materials or sphagnum peat with vermiculite or perlite are good.
Avoid high salt levels, indicated by a yellow or white crust on top of the soil or at the soil line or drainage hole. When watering, allow the water to drain through the container and then empty the saucer. Leach your houseplants every four to six months by pouring excess water into the soil and letting it drain completely.
This University of California website is a good source for houseplant information.
• The Green Thumb is a column by Tracy’s master gardeners. University of California-certified master gardeners are available to answer gardening questions from 9 a.m. to noon Tuesdays, Wednesdays and Thursdays at 953-6112 or firstname.lastname@example.org.