Understanding how often to water your houseplants plays a key role in keeping them live and healthy. The main factors that contribute to the watering needs of a plant include:
The plant’s origin
Plants will require different levels of watering depending on their origin. Looking at the natural environment of where a plant originates from provides the best indication of how the soil should be kept between watering, which helps in understanding how often a plant should be watered. If the natural environment of the plant is a forest floor of a rainforest then the plant is likely used to frequent rainfall. Therefore this plant would require more frequent watering where the soil is evenly moist. Whereas if a plant is native to an arid desert environment, which is a drier environment and rainfall is less frequent, the plant will require less frequent watering allowing the soil to dry out between watering.
Summer vs Winter
The time of the year also plays a role in how often you should water. Now that we are coming into winter, plants begin to enter a rest period and require significantly less water than in spring and summer. During spring and summer, plants require more water as they are going through growth period. As such, the same plant that requires moist soil in spring and summer would need the soil to dry out for a day or two in winter between watering. There are many other factors that influence your plant's health during the different seasons. These include light exposure, temperature, and humidity.
Light exposure inside a home varies between winter and summer, and although summer is associated with higher light exposure outdoors, during winter the sun is higher on the horizon (increasing the brightness indoors) and lower on the horizon in the summer (decreasing the brightness indoors). In addition, surrounding trees and shrubs may block sunlight with their leaves in summer, allowing for more light during the winter after their leaves have fallen off.
Temperature obviously varies between the seasons, with summer having higher temperatures than winter (and consequently requiring more water). In general, plants grow faster with increasing air temperatures. However, temperature can also have indirect effects on plants. A warm winter may result in a larger insect population the following season (so always check for insects & disease before making any drastic changes to your watering routine).
Humidity is another important factor to consider in determining the watering needs of your plants in relation to the different seasons. Humidity refers to the amount of moisture in the air, and may or may not be associated with precipitation. High humidity reduces water loss from plants, and may increase the chance of disease. Humidity substantially reduces during winter compared to summer, hence, misting your plants (but not too much, or disease can become a problem) or purchasing a humidifier can ensure your plants remain healthy during winter.
Location of the plant
The physical location of your plant has important implications on how much water your plant requires. In general, plants respond better to more light, but the more light a plant receives the more water the plant requires. In the sun or in the brightest spot the plant would require the most amount of water, not only due to evaporation but also cause in a brighter spot the plant would grow quicker compare to a darker spot. Therefore the further away a plant is placed from light reduces the amount of water needed. Less light can also slow down the growth of the plant. If you're serious about looking after your indoor plants, learn about foot-candles (the unit of light measurement for plants) and consider purchasing a light meter or photographic exposure meter, so you can accurately measure the light levels in certain areas of your house. Check out http://extension.illinois.edu/houseplants/needs_light.cfm for more information on houseplant lighting requirements.
Air conditioner and heater
Indoor plants are also impacted by artificial heating or cooling, which dries out the air. Plants that require high level of humidity such as tropical plants would need extra care. Misting the plants help with retaining moisture in the air, keeping the leaves looking fresh and healthy. It’s important to ensure there is sufficient air circulation when misting so the leaves can dry out as misting too often can lead to pest infestation. Placing a tray with pebbles and covering half of it with water can also help with creating humidity. It’s important to make sure, there is a some space between the water and pot plant so the plant is not sitting in water as it would be detrimental to the plant’s health.
The pot size
The size of the pot plant determines how much water to use to water the plant. As indoor plants are grown in a pot, the amount of nutrients available to the plant is contained within the pot. Therefore when watering your pot plants, you want to use enough water so some water, i.e. the excess water, could drain out from the bottom of the pot but not too much water, which will flush out the nutrients in the soil. While the soil shouldn’t be flushed every time you water, it is a good idea to flush out the soil every now and then to get rid off excess salt build up. You just need to ensure the nutrients in the soil is replaced with sufficient plant food.