How Much Water Per Cannabis Plant in Soil?
A cannabis plant in soil needs about 10 to 15 percent of its pot volume per watering. That is 2 to 3 quarts for a 5-gallon pot, about 1 gallon for a 7-gallon pot, and about 1.5 gallons for a 10-gallon pot. Water again when the top 1 to 2 inches of soil feel dry, which for a plant in veg usually means every 2 to 3 days.
Cannabis Watering Schedule for Outdoor Pots
Water amount and water timing are two separate decisions. New growers mix them up, then either drown the roots or let the pot bake to dust. The fix is a repeatable check plus a rough number to start from.
cannabis watering schedule by stage
Watering Amounts by Growth Stage and Pot Size
- Seedling, 1-gallon pot: 1 to 2 cups every 2 to 3 days, poured in a ring around the stem.
- Early veg, 3-gallon pot: about 2 quarts every 2 to 3 days.
- Late veg, 5-gallon pot: about 3 quarts every 2 to 3 days.
- Early flower, 5-gallon pot: about 1 gallon every 2 days.
- Peak flower, 7-gallon pot: about 1 gallon every 1 to 2 days.
- Late flower, 7 to 10-gallon pot: 1 to 1.5 gallons every 2 to 3 days, tapering as you near harvest.
Treat these numbers as a starting line, not a law. A 5-gallon plant under a 600-watt light in 85F air dries out much faster than the same plant in a 70F tent under a small LED.
When to Water Cannabis Plants: Signs to Look For
Why Pot Size Sets the Ceiling on Water Volume
Roots need oxygen as much as they need water. A pot holds a fixed volume of soil, and that soil holds a fixed amount of water before every air pocket fills. Leave the pot soaked for days and the roots suffocate.
how often should i water cannabis plants
Watering to 10 to 20 percent runoff makes sense in coco and salt-based nutrient programs because it pushes old salts out of the root zone. In living soil or rich organic mixes, light runoff now and then is fine, but soaking to heavy runoff flushes the microbes and nutrients you paid for.
Fabric pots change the math. They breathe through the walls, so they dry from the sides as well as the top and often need water a day sooner than plastic.
How to Tell When Soil Is Dry Enough to Water
Finger test
Push one finger 2 inches into the soil. Dry and clean means water. Soil clinging to your skin means wait.
Lift test
Pick up the pot before and after watering. The weight difference teaches you more than any schedule. After a few weeks you can judge a dry pot by feel alone.
Moisture meters
Cheap two-prong meters read the same soil in different ways at different depths, so use them as a hint and not a verdict. A two-prong meter still beats guessing on a 10-gallon pot you cannot lift.
Signs You Are Watering Wrong
- Overwatered: leaves droop and curl down, stems stay stiff, growth stalls, topsoil grows green algae, and fungus gnats show up.
- Underwatered: leaves droop from the stem, edges turn crisp, soil pulls away from the pot wall, and the pot feels feather-light.
- Watered right: leaves sit flat and reach for the light, the pot feels heavy after a soak and light 2 days later, and no water sits in the saucer.
One soaked afternoon will not kill a plant. A week of wet feet will. When in doubt, wait a day.
What Changes How Much Water a Plant Uses
- Temperature: 85F air pulls water out of soil far faster than 72F.
- Humidity: 60 percent relative humidity slows transpiration, while 35 percent speeds it up.
- Airflow: a fan moving across the canopy dries the top layer of soil.
- Light: more light means more photosynthesis and more water pulled through the roots.
- Plant size: a 4-foot plant in flower moves gallons per week, a 10-inch clone moves cups.
- Medium: peat and coco hold water well, while sandy or perlite-heavy mixes drain fast.
Water Quality and Pouring Technique
Soil buffers pH, so aim for 6.3 to 6.8 on the way in. Water at 65F to 72F keeps roots comfortable, while ice-cold tap water shocks them.
Pour slow, in circles, and cover the whole surface instead of one spot near the trunk. Dry peat and dry living soil repel water, so add a little, wait, then add more. Stop when the first drops hit the saucer.
Frequently Asked Questions
Should I water a cannabis plant in soil every day?
No. In a 5-gallon pot, a plant in mid-flower usually drinks every 1 to 2 days, and a plant in veg drinks every 2 to 3 days. A plant that needs water each day is telling you the pot is too small or the room is too hot.
How much water does a cannabis plant use per week?
About 2 to 4 gallons per week for a 5-gallon pot in mid-flower, spread across 3 or 4 waterings. Small plants in veg use far less, often under a gallon per week.
Can one watering be too much?
Yes, if the pot has no drainage holes or you leave the saucer full. Waterlogged soil with no air exchange is the main cause of root rot indoors.
Do I need runoff every time?
No. Runoff belongs to salt-based feeding schedules. In organic soil, water until the soil is moist all the way through and stop there.
Bottom Line
Give a cannabis plant in soil about 10 to 15 percent of its pot volume, then wait until the top 2 inches dry out. Lift the pot, check the soil by hand, and let the plant tell you when it is thirsty.