There really is no such thing as a houseplant; they are just outdoor plants that we have discovered tolerate living indoors as long as we take care of them properly. Sort of like neutered cats.
All plants need the following to survive, whether growing in tropical jungles or on your kitchen windowsill: sunlight for energy; water; air; a source of nutrients; tolerable temperatures; something to grow in/or on. We can add some additional flourishes—proper humidity and freedom from, or tolerance of, diseases and insects or other munchers that would like nothing more than to invite them to dinner.
As a guide, it never hurts to Google your plant and find out where it comes from—Desert? Jungle? Clinging to a tree branch? This provides hints as to how much light or water the plant needs. Plants that come from the understory of a tropical rainforest are likely to tolerate low light. Plants that live in more open areas and originate in countries with a defined wet and dry season probably will tolerate drying out between watering. Beyond using your search engine, there are folks in our houseplant department that just love to talk about plants, and they can point you to the easy-to-care for types. Or, look at the plants in your office or the shopping mall or your doctor’s reception room: if these plants that are doing well, they will probably also do well in your apartment or home.
Briefly, here are some pointers about houseplant care.
Light: sunlight powers plants through the chemical process called photosynthesis, combining carbon, oxygen and hydrogen in the presence of chlorophyll–the nifty stuff that makes plants green—to form sugar. Depending on where they evolved, plants have different abilities to tolerate low light intensities. Indoors, we generally have poor light conditions. Light intensity drops quickly with distance from a window, and light travels in straight lines (it doesn’t bend around corners), so plants that aren’t actually on the windowsill are receiving much less light (energy) than they would receive outdoors. It’s not obvious to us because our eyes adjust to the lower light. So, start with the spot in which you want to put a plant: something tall in a corner, ten feet from the window? What direction does that window face—(do you see the sun in the morning only? East. Never? North. Afternoon only? West. All day? South.) South-facing windows get the most light but may also be too hot for many plants during the summer. So in that corner in a north-facing room…how about a nice floor lamp instead? Or try a corn plant (dracaena) but it would be best to rotate it to a brighter spot every few weeks and replace it with another, if you want your plant to survive for a few years.
Water and “Soil:” plants need water for photosynthesis, cooling, and turgor (that is, to prevent wilting). They also need some air around the roots because the roots need oxygen for metabolic reactions, just like animals do. So, you have to have a balance between moisture and air, otherwise the roots die (root rot). We create an artificial “soil” in our potting mixes—no actual soil/dirt/earth—to ensure that we have a light-weight medium for the roots, a medium that can hold water but also lets excess water drain out of the pot, leaving air spaces for the roots to be happy. The potting mix is light when dry: lift the pot; if it’s light, go ahead and water; if it’s relatively heavy, let it go for another day or two. You will develop a rhythm, you’ll know that some plants need to be watered every three or four days, others may go weeks between waterings. Wilting: if a plant loses turgor, lift the pot; if it’s light, water it. If it’s very dry you may need to soak it in a bucket of water for an hour or water several times at the sink; dry potting soil shrinks away from the side of the pot and most of your water may just be running between the side of the pot and the soil until it soaks long enough or is watered enough times to absorb enough water to swell back to contact with the pot. If the plant is wilting and the pot is heavy (soil is wet), then, unless it’s very warm in the house, you probably have overwatered, have a root rot, and should just throw the plant away. (Take it out of the pot: young, healthy roots are white. Sick roots will be discolored, mushy, and the potting medium may smell like a gutter.)
Air: If you can breathe, so can your plant! Houseplants like air movement, they do best in comfortable temperatures (mid-60’s to low 80’s for the most part), and depending on the plant, they may need supplemental humidity when the furnace is on. I think a furnace humidifier is good for most plants; keep them away from the heating/cooling vents. I don’t think misting does any good. I also don’t believe that houseplants do all that much good at cleansing the air; I think that’s way overhyped. If you think your little old philodendron is going to clean the 700 cubic feet of air in a 10 by 10 by 7 foot room, more power to you. Heck, your houseplant is barely alive, coping with marginal living conditions, it’s not a little green Dyson.
Fertilizing: as mentioned above, plants get their energy from light. Fertilizer is not food in the sense we think of food—as fuel. Fertilizer is like your mineral supplements—your calcium and iron, not your bowl of ice cream. Plants need something like 17 elements to survive, most of which are absorbed by the roots from the soil. Given that your plant is limited by its life in your pot and it can’t grow out and find these nutrients, it’s up to you to provide them. So, if the plant is getting proper light and water and is trying to grow, fertilizer will allow it to add more leaves, stay green, have strong stems, etc. If the plant is sickly because its primary needs for light and water are not being met, then “feeding it” is not going to help, and may actually push the plant into weak, spindly growth. In winter, when days are short and light intensity is lower, most houseplants go into a sort of dormancy, and they don’t require much fertilizer. As spring arrives, you may see new leaves starting to emerge, and then you may start to fertilize. I use Jack’s Classic water-soluble fertilizers; you may prefer organics. Whichever, follow label instructions, with a grain of salt (figuratively speaking). The label is going to be making recommendations for plants growing in optimum conditions, which you, my friend, are unlikely to have. So in my experience, you will do fine to reduce the frequency or the concentration of your houseplant “food” considerably from the recommendation. And, like ice cream, adding another scoop may sound like a good idea, but it can do lots of bad things, so less is better than more.
The Enemy: there are only a few insect pests of houseplants, and usually the air is too dry in the house to have much trouble with plant diseases (except root rot). The best defense against insects is to buy “clean” plants to start with, and learn to recognize an infestation before it gets out of hand. The biggest problems are: spider mites (worse in hot, dry conditions); mealybugs and scale; aphids; thrips; whitefly. Unless your plant is an heirloom or has some special significance to you, an infested plant is probably best discarded before the bugs spread to others. These are all tiny, yet prolific, sucking insects, so you won’t see holes in the leaves from chewing; the symptoms are usually discoloration or distorted growth, possible accompanied by a black coating of mold on the leaves that grows on some of the sugary sap left on the leaves by the little suckers. There are not many chemical options available to deal with these bugs: mostly oils, insecticidal soaps, or Neem oil; mites and aphids may be controlled with just a strong spray of plain water. If you are girding for battle, our “Garden Pharmacy” staff will help you select the best product.
Insects tend to thrive in dry, heated air in the house. They are tiny; you might bring them in on your clothing if you have been gardening, they may be on the plant if you have had it outdoors for the summer; mites are easily small enough to come in on the breeze through a window screen. You may have even bought the problem with your new plant, so inspect before you buy!! Because of environmental and staff safety concerns, commercial growers and houseplant retailers have fewer pesticide options these days, and scale and mealybugs are very hard to control, and you may notice these pests on palms (for example) months after you buy them. So it’s always a good idea to look at your plant’s stems, at the new growing tips, and under the leaves every few weeks. You might find the beginnings of an infestation while there is still time to control it.
by Larry Hurley, Behnke horticulturist