MOST avid gardeners don't check their love of plants at the front door. We keep ferns in the bathroom, begonias in the study, a dwarf citrus in the bedroom, pots of rosemary in the kitchen, and seedlings in the basement. Today there are so many interesting plants that can be grown indoors that there's simply no reason for a gardener not to be surrounded by plants all year-round.
The more you know about your indoor plants and where they come from, the easier it will be to keep them healthy. Understanding a plant's native habitat can help you decide which potting soil to use, how often to water, what window the plant should be in, and whether or not it needs extra humidity. But even if you don't have specific cultural information about each and every one of your houseplants, you can feel your way to success with some general guidelines.
A Few Words of Comfort
Plants have a lifespan, just as people do. If you have a struggling houseplant that has been around for a few years, it may simply be tired, and all the TLC in the world may not be able to revive it. Consider starting over with a new plant. Remember that unhealthy plants attract insects like a magnet, and when the infestation spreads to your other plants, you may regret your earlier large-heartedness.
Gift plants, such as cinerarias, poinsettias, chrysanthemums, azaleas and cyclamen, make wonderful indoor decorations, but in most cases they should be discarded after they have finished flowering. Some of these plants can be nursed along to flower again, but it is usually difficult to provide the growing conditions they need for another lush display of blooms.
The Right Soil
If possible, your potting soil should be tailored to the particular type of plant you are growing. Cactus, succulents and rosemary, for example, prefer a coarse, well-drained soil that is about one-third sand. Seedlings should be grown in a light, moisture-retentive, soilless mix. African violets and ferns prefer soil with a high humus content, which can be achieved by adding leaf mold or shredded bark. Many kinds of orchids are happiest growing in nothing but fir bark or sphagnum moss.
A good indoor potting mix is usually composed of peat moss, vermiculite and perlite. These soilless mixes absorb moisture very well and resist compaction, but they tend to dry out very quickly. Since they do not contain any nutrients, you must provide your plants with a consistent supply of fertilizer. One advantage to a soilless mix is that it is sterile, so there is no chance of introducing pest or disease problems.
Many gardeners add organic components to their indoor growing mix. These might include leaf mold, finished compost, composted peat, or rich garden soil. A growing medium that contains 10 to 20 percent organic matter will usually not dry out as fast as a soilless mix, and it also allows you to introduce beneficial microorganisms and nutrients.
The most critical consideration when you're purchasing or blending your own potting soil is to ensure that the mix is light enough to provide adequate pore space for air, water and healthy root growth. Month after month of overhead watering, without the benefit of earthworms and weather to aerate the soil, usually results in an unhealthy, compacted root zone. To ensure that your plants' roots have the oxygen they need for healthy growth, your potting soil should contain plenty of perlite, vermiculite, or sharp sand. This will allow water to drain freely, and ensure that the soil is at least 10 to 20 percent air.
Climate, Water and Nutrients
Temperature: In their natural habitat, most plants experience a day-to-night temperature fluctuation of at least 10 degrees F. In your home, they will benefit from having a similar temperature differential. Most plants also expect a resting period each year; in fact, some flowering plants actually require a period of dormancy before they will set bud and flower.
To simulate this resting period, you should cut back on water and fertilizer during the late fall and early winter, when the intensity and duration of natural light is lowest. Once the day length begins to increase, you can declare it to be spring, and step up the water and fertilizer. Your plants will respond with healthy new growth.
Humidity: Most plants are happiest when the relative humidity is 50 percent or higher, though they can usually survive at 30 to 40 percent. If the air is much drier than that, they are unable to absorb enough water through their roots to keep up with the water lost through their leaves. Unfortunately, indoor air, especially in the winter, often has a humidity as low as 10 to 20 percent.
Misting your plants helps, but only for an hour or so. A better solution is to use a cool vapor humidifier (which you will benefit from as well). You can also cluster your plants together so that, as they release moisture into the air, they'll humidify their neighbors. Or try arranging your plants on a gravel-filled tray that contains about 1/4 inch of water. As the water evaporates, it will humidify the air around your plants. Just be careful that the pots don't sit directly in the water.
Water: More houseplants die from overwatering than from anything else. The best advice is to resist the temptation to water on a regular schedule. Your plants will require frequent watering if the weather has been sunny and warm, and they may not need a drop if the weather has been cool and cloudy. Make a habit of checking the soil of at least a few indicator plants, and water only if it feels dry to a depth of ½ to 1 inch.
When you do water, drench the root ball until you can see some water seep out the bottom of the pot. This will ensure that the entire root ball gets moistened. Small pots will benefit from being soaked in water for about an hour, once a month. Whenever possible, try to water your plants with room temperature water to avoid shocking the roots.
Never use water that has been chemically softened. It contains salts that are harmful to plants. If your water is very hard, consider installing a demineralizing attachment to filter out impurities, such as lime and chlorine.
Nutrients: Indoor plants are usually not too fussy about fertilizers. The most important thing is to not overdo it. Follow the instructions on the package, and err on the weak side. Always water your plants thoroughly before applying any sort of fertilizer. A standard 10-10-10 formulation is fine for most indoor plants.
Supplementing with an organic amendment such as liquid seaweed or fish emulsion, or a biostimulant, will provide some of the trace nutrients lacking in an inorganic plant fertilizer. A top dressing of compost or worm castings is another effective way to add organic nutrients. Be aware that some plants are particularly sensitive to pH level, and that this sensitivity can be either exacerbated, or corrected, with the right fertilizer. To avoid the buildup of fertilizer salts, it's a good idea to periodically drench the soil with clean water, then water again with clean water. This will help flush any salts out of the soil.
Providing Adequate Light
Plants differ greatly in their need for light. Some will be happy with the diffused light from a north window. Others will languish if they don't receive 12 hours of bright light all year-round. Knowing the light requirements for each of your plants will allow you to determine where they will be happiest. Here are some general guidelines for matching plants to various locations in your home.
Most flowering plants, and some sun-loving foliage plants, need to be within 3 feet of a sunny, south-facing window.
Plants that prefer bright, indirect light can be located 3 to 5 feet away from a south-facing window, or within 3 feet of an east- or west-facing window.
Plants that thrive in diffused light can be placed 6 to 8 feet away from a south-facing window, or within a foot of a north-facing window. In that location they'll receive about 25 percent of the light they would get if they were in front of the sunny, south-facing window.
During the winter months, you may need to move all of your plants closer to the window in order to compensate for the decrease in light.
Most plants perform best when they receive 12 to 16 hours of light per day. If you want to keep your plants blooming during the short days of winter, you may need to provide supplemental lighting.