Definition - What does Deep Watering mean?
Deep watering is the process of completely drenching a plant’s root system to ensure that it gets a more than adequate supply of water. Generally, to deep water a plant, the water must soak at least eight inches or more beneath the soil’s surface.
The process of deep watering is highly beneficial because it encourages a plant to develop a deep, diverse, strong root system that will sustain it during times of drought.
MaximumYield explains Deep Watering
Deep watering is commonly done only once per week, unlike shallow watering methods that may be required three or four times per week. This frequency of deep watering only once a week ensures the plant is never overwatered. Some plants, like succulents and other ornamental houseplants, won't even require deep watering that frequently, and can get by with monthly waterings.
Deep watering is a favored irrigation method in regions that experience severe heat and drought.
Plants that are watered using a shallow irrigation method will never develop a deep root system because the ability to get adequate water at the soil’s surface discourages the plant’s roots from reaching deeper.
A shallow root system is dangerous in regions that suffer from drought and heat because the top few inches of soil quickly dries out, cracks, and exposes the plant's roots to the harsh sunlight where the tender roots will rapidly bake. The plant will perish if it does not have roots that are deep enough to reach the moist, protected, cooler soil.
However, there are times when a shallow irrigation method is preferred, such as in climates that get plenty of rain. Specific crops don't require extensive root systems, so that's also something to consider.
Deep watering should not be confused with overwatering, which is the practice of watering too frequently, or much more often than is needed. In the case of accidental overwatering, a plant's root zone essentially suffocates.