Greenhouses provide a protective environment to grow plants, including during winter months when growing outdoors is impossible. Yet, the protection of the greenhouse does not completely isolate plants from the outside environment. As conditions change outdoors so do conditions inside the greenhouse and your plants' watering needs change alongside greenhouse conditions. You need to consider your plants' basic needs and use proper watering techniques.
Water When Needed
Water only when the soil feels dry, easily determined by sticking your finger in the soil and feeling for moisture. If the soil contains peat moss, use its color as an indicator; when dark brown the soil is wet while a tan color soil means the soil is dry. Many plants do not require watering every day in the greenhouse environment. Consider that watering needs vary with each season as warm summer months shine their rays through the greenhouse walls and dry plants out quicker while winter months, with their cloudy cool days and limited sunlight, allow plants to retain moisture. While over-watering is dangerous to a plant's health, under-watering a plant is just as harmful. Water plants before the soil becomes too dry and before a plant starts to wilt.
Drip irrigation systems provide for an effective watering option. It sits in the pot's soil and provides a slow, steady drip of water to keep plants moistened without over-watering. They protect plants from receiving heavy water on its leaves and protect young seedlings that have yet to gain enough strength to handle the weight of much water. Another option, especially for mature plants, is a misting system that sprays a gentle mist of water on top of the plants. Use room temperature water when utilizing any watering method.
How Much to Water
Know how much to water, not just when to water. While a relatively easy task, those just focused on watering the plant may tend to over-water it. Water the soil enough to saturate it. Stop watering when water begins to run out of the drainage hole on the pot's bottom.