For a cannabis plant grown in soil, plan on about 0.5 to 1 gallon of water per plant at each watering for a 5-gallon pot, two to three times a week in vegetative growth and up to once a day in late flower. The exact number depends on four things: pot volume, plant size, growth stage, and how fast the soil dries where you grow. The dependable rule is not a fixed volume. It is watering when the top 1 to 2 inches of soil are dry, then giving enough water to soak the full root zone.
The short answer
A 5-gallon soil pot takes about 0.5 to 1 gallon per watering. Smaller pots take less, larger pots take more, and frequency matters as much as volume. If you pour 1 gallon into a 3-gallon pot every day, you will drown the roots. If you pour 1 cup into a 10-gallon pot every three days, the lower root zone stays dry and the plant stalls.
Cannabis Seedling Watering Schedule: First 2 Weeks
How much water by pot size
These amounts are starting points for a plant in mid-vegetative growth under indoor lights. Adjust up or down based on how the soil feels.
When to Water Cannabis Plants: Signs of Thirst and Overwatering
- 1 to 3 gallon pot: about 1 to 2 cups per watering
- 5 gallon pot: about 0.5 to 1 gallon per watering
- 7 gallon pot: about 1 to 1.25 gallons per watering
- 10 gallon pot: about 1.5 to 2 gallons per watering
Pour until about 10 to 20 percent of the water runs out the bottom. That runoff tells you the whole pot is wet, not just the top layer.
How often to water cannabis in soil
Frequency follows the dryback, not the calendar.
- Seedlings and clones: small amounts near the stem, often every 2 to 3 days in small cups
- Vegetative plants: every 2 to 3 days in a 5-gallon pot
- Early flower: every 2 days
- Late flower: every day to every other day for large plants in warm rooms
What changes the number
Two growers with the same pot size can need different volumes. These factors move the number most:
- Pot material: fabric pots lose water faster than plastic or ceramic
- Temperature and humidity: a hot, dry room pulls water from the soil in hours
- Airflow: strong fans over the canopy increase transpiration
- Plant size and root mass: a large plant in a full pot drinks more than a small one
- Soil mix: peat and coco blends drain faster than heavy compost
- Light intensity: stronger light means more growth and more water use
Signs of overwatering
- Leaves droop and stay droopy after the soil dries
- Lower leaves turn yellow and soft
- Growth slows for days
- Fungus gnats appear around the pot
- Soil smells sour and stays wet past four days
Signs of underwatering
- Top 2 inches of soil crumble to dust
- The pot feels light when you lift it
- Leaf edges crisp and curl up
- Soil pulls away from the sides of the pot
- Water runs straight through the pot on contact
If water runs straight through, the soil has gone hydrophobic. Water in two or three passes with a short pause between them so the medium can absorb it.
A simple watering routine
- Push a finger or a moisture meter 2 inches into the soil.
- Lift the pot to judge weight. A dry 5-gallon pot is light.
- Water at a slow rate around the perimeter, not just at the stem.
- Stop when 10 to 20 percent of the volume runs out the bottom.
- Empty the saucer after 15 minutes.
- Wait until the top 2 inches are dry before the next watering.
Water quality and pH for soil
Soil buffers pH better than coco or hydro, so a range of 6.0 to 7.0 works for most grows. Tap water in most US cities is fine to use. If your water is very hard, let it sit overnight or mix it with filtered water. Cold water straight from the tap can shock roots, so let it reach room temperature first.
When to change your approach
If the soil stays wet for more than four days, the pot is too large for the plant, airflow is too low, or the mix holds too much water. If the soil dries in a single day, the pot is too small for the plant or the room is too warm. Both problems are solved with pot size, airflow, and a soil mix that drains. For growers in states with legal cannabis programs, your local retailer or cultivation shop can help you match a soil blend to your room.