The most common cause of house plants dying is over-watering. Plants need to be able to absorb oxygen through their roots. If the potting medium is completely saturated, all the air will be pushed out, and the plant’s roots will simply suffocate.
Another factor is that house plants seldom enjoy the best possible lighting conditions, so they grow significantly more slowly than they would under natural conditions. For this reason, they need less water and will cope best if watering is adapted to their limited needs.
As a general rule, therefore, let the potting medium around your plants dry out somewhat between watering, and avoid watering excessively.
The frequency of watering depends very much on the size of the pot, as well as on the temperature and light conditions. Generally speaking, the need for watering is significantly greater during the summer months, and if the plant is in direct sunlight or above a radiator or on a floor with underfloor heating. Small pots will also require more frequent watering than large pots.
Of course, different species of plants have individual requirements and drought tolerances, but the following rule generally applies: poke a finger into the soil to find out whether or not the potting medium feels wet. If the medium feels wet, give watering a miss and check again in a week’s time. Keep plants generally on the dry side during the winter months.
It is a good idea to use rainwater for watering your plants. Tap water can contain substances that the plant is unable to absorb and which will therefore eventually build up in the potting medium. These substances can alter the degree of acidity in the potting medium and restrict the ability of the roots to absorb the nutrients they need.