Grow Calculator
Watering Volume Calculator
Give each plant the right amount every time — enough to hit runoff, not so much that roots drown.
1 gal
per plant, per watering
3.8 L
per plant in litres
4 gal
mix this much per feed for 4 plants
9.3 gal / week
total tent consumption
That is 20% of container volume — enough to reach saturation and produce 10-20% runoff. pH to 6.2-6.5 in soil or 5.8-6.2 in coco before it goes in.
Volume scales with roots, not pots
A seedling in a 5 gallon fabric pot does not want 1.25 gallons of water. Its roots occupy a tiny fraction of the medium, and soaking the whole container leaves cold, waterlogged soil the plant cannot use. Water a small circle around the stem and widen it as the plant grows.
The lift test beats any schedule
Pick up the pot right after watering, then again when it is dry. Learn those two weights. That single habit prevents both overwatering and underwatering better than any calendar reminder ever will.
Wet-dry cycles build roots
Roots chase moisture. Letting the medium approach dryness before the next feed drives root expansion and pulls fresh oxygen into the rootzone. Constantly saturated soil produces shallow roots and invites root rot and fungus gnats.
Common questions
- How much water does a 5 gallon pot of cannabis need?
- Roughly 1 to 1.25 gallons per watering once the plant fills the container, aiming for 10-20% runoff. Young plants in the same pot need far less — water only the root zone until roots colonise the medium.
- How often should I water cannabis?
- By weight, not by schedule. Lift the pot: water when it feels light and the top inch or two is dry, typically every 2-3 days in soil and daily or more in coco. Mature plants in late flower drink noticeably faster.
- Why does runoff matter?
- Runoff carries accumulated salts out of the medium. Without it, EC climbs in the root zone until the plant cannot take up water properly, producing symptoms that look like deficiencies but are actually excess.
- Can I overwater a cannabis plant?
- Yes, and it is the most common beginner mistake. Overwatering suffocates roots by displacing oxygen. Drooping with a heavy, wet pot means too much water; drooping with a light pot means too little. Fabric pots make this much harder to get wrong.