Definition - What does Leaching mean?
In the most basic sense, leaching is the act of access irrigation water exiting the growing media, most often through the bottom of the container. The access water usually contains so level of nutrient salts and is called 'leachate'—a liquid that has ran through a solid and leached out some of the constituents.'
The term leaching is also used when a farmer opts to irrigate a small field with large quantities of water to remove salt build up in the soil. When done on a smaller scale by indoor farmers, this can be called flushing, flushing your plants, or flushing the grow medium.
MaximumYield explains Leaching
In a negative connotation, the term leaching may also refer to soil that has lost valuable nutrients due to too much leaching. The loss of key nutrients in soil usually occurs from rain, flooding, or excessive irrigation.
Soil leaching is very dangerous, especially when it allows chemical and pesticides to leak into the groundwater. Anytime it rains, minor leaching occurs but this is acceptable because it breaks down organic material and resupplies the soil with nutrients. However, flooding washes all nutrients away.
Leaching is a type of filtration that is performed by the soil. The soil can effectively leach out harmful substances. However, sandy soil is especially porous and may not successfully work as a filter, so irrigation water just flows through it, taking valuable nutrients along with it.
The most common nutrients that are leached from the soil are nitrogen and sulfur. The pH of the soil is also altered during leaching and the pH level can drop dramatically. Soil microbes are washed away by the water and earthworms killed.
Potted plants often require leaching because salt can build up on the soil’s surface. Leaching potted plants (flushing) entails pouring an excessive amount of water into the pot to completely remove the salt accumulation.