Light and water are the two main factors that cause a houseplant to go south. A typical houseplant is lives in the understory of a tropical rain forest where it gets filtered light until it grows big enough to reach up into the canopy for brighter light. They're used to lots of warm rain but perfect drainage, too. We put them into pots inside our homes where they have much different conditions to contend with. Most houseplants would like bright filtered morning sun by an east window but many will tolerate darker locations if you adjust your watering to accommodate the slower growth rate.
Water just enough to keep the soil from going totally dry. Poke your finger into the soil. As a rule of thumb, if your plant is in a 4-6" pot let the soil dry half an inch down between waterings then water thoroughly with room temperature water. Don't let the pot sit in a saucer with water for over an hour or the roots will rot. If your plant is in an 8-12" pot let the soil dry to 1-2" down before watering and if you have a bigger specimen the soil should be dry 2-3" down before watering. Don't panic if this takes 2-3 weeks before the soil has dried sufficiently for a plant in a big pot. A moisture meter is very helpful for your larger plants.
I'm like the cobbler who has holes in his shoes when it comes to plants. I love to have lots of them around but they have to be tough and easy to care for. If you have have medium to low light conditions like me in your house some of my favorite upright plants are split-leaf philodendron or philodendron selloum, spathiphylum (peace lily), Chinese evergreen, cast-iron plant, schefflera, arobicola and parlor palm. The low-light hanging plants that I love are the heart-shaped philodendron, pathos and grape ivy. Most of these houseplants grow naturally in low-light areas of the jungle.
Houseplants don't like to be transplanted during their dormant period in the winter. They are slow to grow new roots at this time. You can transfer a plant to a new pot that is about the same size or a just a little bit bigger if you need to but it's better to put off any major potting projects until spring. Remember to choose a pot only 2" bigger than the old pot each time you transplant. The soil can dry between waterings this way allowing oxygen to move into the root zone.
Fertilize less often. Some houseplant growers skip fertilizing in December and January, starting up again with half strength fertilizer in mid-February. Think of your houseplants as essentially dormant in winter. They need fertilizer only when active growth resumes.
Avoid cold drafts. Most houseplants can handle slightly cooler temperatures at night but detest blasts of chilly air. Avoid placing most plants near drafty, high-traffic areas such as a foyer or hallway. Ficus trees are famous for dropping leaves when exposed to temperature changes.
Plants get dusty decreasing the amount of light they can use to photosynthesize. Insects such as spider mites actually thrive in dusty conditions. Take your plants to the kitchen sink or tub every few months and wash them off with lukewarm water or use a moist cloth or paper towel to wipe the dust off the leaves. In the summer when it's warm you can wash them off outside with the hose in the shade but it's too cold now for this. How would you like to have a cold hose turned on you these days?
If you do find insects on your plants, a spray of mild insecticidal soap for houseplants usually does the trick if you do a follow up spraying a week later. Horticultural oil works well, too, by smothering the insects and its eggs. If you have little black fungus gnats flying over the soil, you are watering too frequently. They feed on the algae growing on moist soil. Scrape off the surface, spray with insecticidal soap and let the soil dry out.
Many common houseplants help fight pollution indoors. They are able to scrub significant amounts of harmful gases out of the air through the everyday processes of photosynthesis and I'll tell you which ones are the most effective in an upcoming column.
- Jan Nelson, a landscape designer and California certified nursery professional, will answer questions about gardening in the Santa Cruz Mountains. E-mail her at firstname.lastname@example.org, or visit www.jannelsonlandscapedesign.com to view past columns and pictures