Soil Moisture in cannabis cultivation grown in contained medium.
Since the indoor cultivation of cannabis is primarily aimed at producing the heaviest flower production in the least amount of time, the ideal soil moisture is one that will encourage the heaviest root production as soon as possible with the least amount of stress.
When a seedling is transplanted into a new larger container, the root system is isolated within the confines of it's previous container, and suspended in a much larger volume.
A good wet dry cycle consists of allowing the plant to take up all readily availible water in the immediate vicinity of the root system, then allowing the plant to extend it's roots further into the medium in order to reach more moisture. So avoiding the urge to give it more water sooner is very important. Since the medium will wick moisture from the outer areas to the root zone as the moisture levels drop there, the roots are never at risk of dehydration until the container is remarkably low in moisture.
Some might think that the ideal situation in this case would be to give the plant a little water, more often, but this will result in waste toxins from the plant building up in the root zone, and if fertilizers are used regularly, unused fertilizer and salts will build up, locking out nutrient uptake and throwing the pH in the root zone off.
Always give the plant sufficient water to allow some to run through the medium and root system and out of the bottom of the pot. Consider this hygiene.
Keeping the soil too wet will reduce the availibility of oxygen to the roots, causing them to feel like shit and die.
Plants suffering from overwatering (watering too often and keeping the medium saturated) will cause the plant to lose vigor and appear somewhat like the first stages of dehydration, often triggering the smothering instinct in growers and resulting in even more water, like turning fire hose on a drowning man.
Allowing the soil to become too dry will cause the plant to dehydrate, the leaves will wilt due to the loss of moisture, reducing transpiration(1), causing stress that leads to hermaphroditism, as well as reducing the final yield due to the tissue damage.
The surface of the medium evaporates moisture quickly so the surface will appear to be drying out while the bulk of the medium still has a great deal of water availible.
Until you are comfortable with your plants and their needs. A good practice is to keep a pot of the same type that your plants are in, filled with the same medium that your plants are in. Use this to judge the weight of the containers that the plants are in.
When watering you should always add the water slowly so that it seeps through the soil rather then running through it rapidly, creating courses where the bulk of the water travels.
Dry soil has a tendency to repel water at first contact and pockets of trapped air will create bubbles that prevent water from wetting getting to the medium until the free water has passed and the air can travel.
The roots in dryer soil will be freely exposed and vulnerable to nutrient burn. Nutrient enriched water should never be added to dry soil.
I always water in the morning (their morning rarely coincides with my morning...), soon after the lights have come on. This prevents the plants from sitting in saturated containers in the dark, when the least amount of transpiration is occuring.
When the plants are in three gallon containers. I give them each about one quart of clean water with no nutrients or additives, slowly over a period of a minute or two.
Then let them sit for at least ten minutes before adding either water or supplement enriched water.
I then add the liquid slowly, till at least a quart runs out of the bottom, then let them drain fully before retiring them to soak up some morning lumens.
Water in the roots is pulled through the plant by transpiration (loss of water vapor through the stomata of the leaves). Transpiration uses about 90 percent of the water that enters the plant. The other 10 percent is an ingredient of photosynthesis and cell growth.
The soil zone that surrounds and is influenced by the roots of plants.