It's a real challenge to grow a happy houseplant. If your plants are thriving, then you have the right combination of light, temperature, and water. Trying to grow cyclamen is futile because the temperature is usually too high. Cyclamen requires a low night temperature of 50 to 55 degrees F.Camellias , too, drop their buds when the temperature is too high. So do gardenias when the temperature is too low.
Fifty years ago our grandmothers grew beautiful, bloom-laden geraniums in their cool kitchens, but with the constant, even heat in the homes of today, geraniums suffer and the lower leaves drop.
Poinsettias will not flower when the length of the day exceeds 12 hours. This means that when it gets dark outside in the fall, it must also be dark in the room where poinsettias are growing. Even the light from a glowing television set or table lamp is enough to keep a poinsettia from flowering.
While the length of day affects flowering and growth, another factor -- light intensity -- does too. African violets will not flower when the intensity falls below 500 foot-candles, nor will they flower when it exceeds 1,300 foot-candles.
Gloxinias are similar in this respect. Even though they will flower at high light intensity, the blossoms become few and small and the rate of growth decreases when the light intensity exceeds 5,000 foot-candles. Begonias also dislike high light intensities, but they thrive in stronger light than gloxinias and African violets do.
On the other hand, geraniums, cacti, gardenias, coleus, and amaryllis are members of a group that demands full sunlight.
If you are having trouble with your houseplants, it may also be a matter of nutrients and oxygen. This is why potted soil should be watched more than the run-of-the-mill garden soil where your summer flowers grow.
The same soil placed in a pot will not necessarily grow a strong houseplant. One of the reasons is that the roots of the garden plant have a larger area in which to grow, while potted houseplants are confined to a small amount of soil.
When the soil at the depth of one-half inch feels dry, it is time to water; when the soil is moist, do not water.
It's important, however, to water your plants so thoroughly that the water comes out the drainage hole. Then all of the soil in the pot is moist. This ensures a uniform distribution of the water.
If only the upper inch or two of soil is moist, it encourages the roots to form only at the surface. If the soil is allowed to dry out, the roots die and the plant uses its energy to produce new roots instead of producing lush growth and flowers.
Pots should never be allowed to stand in water for more than 10 minutes. If the saucer beneath the pot still has water in it at the end of this time, the water should be emptied out. Warm water is far better for houseplants than cold water, because it moves into the plant more quickly. Ideally it is best to use water that has reached room temperature.
A few years ago it was often suggested that houseplants should be fed every three or four weeks and usually with a fertilizer that was medium in nitrogen and high in phosphorus and potash.
Today, by contrast, it is recommended that a weak fertilizer solution be used once a week. Weekly feeding gives the plant a more constant and even supply of nutrients than less-frequent feeding.
Also, because the soil in the pot breaks down over a period of time, thus allowing the accumulation of excess fertilizer salts, it is wise to repot in midsummer so that the plants can adjust and be ready to provide their beauty in the home come fall.
A final caution: Cooking and heating gas is destructive to plants. The best way to lessen this hazard is for frequent ventilation without a direct draft on the plant. For pest control use nicotine sulfate; for scale, an oil spray.