How the plant uses water
Love of moisture
Easy water lets the plant run at full speed. Dry mix first slows photosynthesis, then wilts leaves, then kills
Tension
As mix dries, water clings harder to particles and costs the plant more energy to pull
Short miss
Even a brief dry spell can finish a plant that has no reserve
Hot days
Peak heat can demand about a half inch (1.3 cm) of water. A 4 foot (1.2 m) plant may want about 3.75 gallons (14 L); a 10 foot (3 m) plant about 25 gallons (95 L)
Soil and soilless rhythm
Cue
Water after the top inch or two (2.5 to 5 cm) has dried a bit, and before the root zone goes dry
Drain
In a porous mix, extra water should leave. Standing saturation without air is the danger
Leach
Overwatering still washes soluble nutrients out and wastes water
Fine texture
Some soils fail because they hold no air between particles, not because they are merely wet
Mulch outdoors
Mulch, pebbles, or sheeting cut surface evaporation and keep soil cooler
Hydro reservoirs
Use
Hydro often uses about one half to two thirds the water of in-ground plants because almost all of it goes through the plant
Top up
Replace what evaporation and transpiration removed, after you test what is left in the tank
Balance
Mix the new water so the combined reservoir stays in pH and strength range
Active systems
Never let drip or flood media go dry. Start around every six hours of light and tighten the cycle as plants grow
Indoor containers and stage
Same cue
Top layer no longer moist, root zone not yet dry
Small plants
They drink less. Raise volume as the canopy grows
Veg vs flower
Vegetative plants usually drink more than flowering plants, but flower still wants easy water for yield
Pre-harvest dry-down
Withholding water for days before cut can shrink yield. The book prefers cutting fertilizer, not water, for flavor