Even before they understand the scientific reasons why, experienced gardeners will tell you that rainwater benefits their plants much more than water that comes from an irrigation system. This knowledge is acquired simply by going out to their garden the morning after a thunderstorm and observing how the plants seem refreshed and full of new life.
Absence of Salt and Chemicals
The municipal water supply is treated with chemicals such as chlorine and fluoride in an attempt to control bacterial contamination. These chemicals are harmful to plants. Homeowners who have water softener systems are adding additional salts to their irrigation water. Rainwater is free of these chemicals.
Rainwater that falls during thunderstorms provides additional nitrogen to the soil, which helps high-nitrogen-consuming plants such as corn grow more rapidly. When lightning discharges during a storm, it converts nitrogen in the atmosphere into a form that is usable by plants.
Removing Dust From Plants
Plants collect solar energy through their leaves and through the process of photosynthesis convert it into the chemical energy the plant needs for growth. Rain removes dust from the leaves of plants that may interfere with the absorption of sunlight.
Flushing Salt From the Soil
In time, salts and chemicals from municipal irrigation water can accumulate in the garden soil, making it less hospitable for plants’ root growth. Rainwater penetrates the soil and drives the salts down away from the roots. In some climates with lower rainfall, such as in the desert southwest, gardeners must periodically deep water their plants to flush salts from the soil that have accumulated during the hottest months, when the plants have to receive extra irrigation to survive.
Acid Rain’s Negative Effects
Industrial pollution caused by the burning of hydrocarbons can result in harmful chemicals such as sulfuric acid being released into the atmosphere. These chemicals combine with water droplets in clouds to form what is known as acid rain. This acidic rainwater can cause extreme damage to the leaves of plants and even alter the chemical balance in the soil, making it more difficult to grow new plants.
Because of the beneficial effects of rainwater on plants--assuming that the atmosphere in the area is not polluted--many homeowners have installed systems to capture rainwater for later use in watering their gardens. Called rainwater harvesting, this process can be as simple as putting a 50-gallon container beneath the drain spout from a roof. The barrel has a screen to collect plant debris before it gets in the container. To water the garden, a flexible tube is connected to a tap at the bottom of the barrel and run into the garden just like any irrigation tube. This system works well with soaker hoses or other drip irrigation methods.