Sub-irrigation is a type of irrigation method that provides water to a plant from beneath the soil surface. This type of irrigation is also called "seepage irrigation," and it is often used to grow various field crops. Tomatoes, peppers, and sugar cane are often grown with the help of sub-irrigation. In addition, house plants can be maintained using this type of irrigation process.

Many plant experts agree that taking care of house plants is easier to do with the help of sub-irrigation. Rather than watering plants from the top, sub-irrigation allows plant owners to utilize a self-watering plant system. Creating a small reservoir of water in the bottom of a plant container allows a plant to soak up water as needed. Unlike the above-watering plant process, watering a plant from the bottom of a container is not hard on the plant.

When seepage irrigation is used in a field, a field's water table must be manually raised in order for a farmer to feed crops from below the soil line. A field's water table refers to the level of the groundwater pressure when compared with the atmospheric pressure. Farms that use sub-irrigation techniques often maintain this type of irrigation through pumping stations, canals, gates, and weirs that lower or raise the water level accordingly.

Seepage irrigation is also widely used in greenhouses. Generally, water used in a greenhouse is sent to potted plants from below. The excess water is then recycled in order to feed other plants in the same manner. Most professional gardeners prefer to maintain plants using this form of irrigation, since plants tend to respond better to seepage irrigation than to other watering methods.

Since plants naturally absorb water from the roots upwards, seepage irrigation makes a lot of sense. Watering a plant by dropping water onto it from above will work, though this is not a natural way to keep plants well-hydrated. In fact, this may be the main reason why many plant owners have a hard time keeping plants alive. Sometimes, watering a plant from above can be damaging to the plant ane even cause dehydration.

Farmers have been using sub-irrigation techniques for decades. Frequently, seepage irrigation is the only way to hydrate certain crops that must be grown in dry climates. Through this type of irrigation, farmers can control the amount of water that a field of crops receives. While relying on Mother Nature is one way to tend to crops, seepage irrigation is the best way for commercial farms to ensure proper hydration.