Cannabis Watering Schedule for Seedlings: How Often to Water

How often to water cannabis seedlings

Water a cannabis seedling when the top 1 inch (2.5 cm) of the medium is dry. In a 4-inch pot at 70 to 77 F (21 to 25 C), that takes 2 to 3 days. A seedling in a small starter cell dries faster, often in 1 to 2 days. A seedling under a clear humidity dome can go 3 to 4 days between waterings.

cannabis watering schedule for hydroponics

Give 10 to 30 ml (2 to 6 tsp) per watering in week 1. Move to 30 to 60 ml in week 2 and week 3 as roots fill the pot. Pour in a ring 1 to 2 inches from the stem. The stem base stays dry, so damping off risk drops.

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Week by week

Week 1

• Medium: starter plug, peat pellet, or 4-inch pot.
• Water: 10 to 30 ml, 2 to 3 times per week.
• Humidity: 65 to 70 percent. Crack the dome vents on day 3 to day 5.
• Nutrients: none in a charged soil mix. Quarter strength in coco or rockwool.

Week 2

• Water: 30 to 50 ml when the top inch is dry.
• Roots reach the pot walls. A 4-inch pot may need water every 2 days.
• Remove the dome if leaves stay flat without it.

Week 3

• Water: 50 to 60 ml. Some pots need water daily under strong light.
• Lift the pot. A light pot means dry medium. A heavy pot means wait.
• Transplant to the final container when roots show at the drain holes.

Signs of overwatering

Leaves droop and curl down. The medium stays dark and wet for days. Green algae or fungus gnats appear on the surface. Growth stalls and the stem base turns soft and brown. Saturated medium blocks oxygen, and Pythium root rot starts in wet, warm conditions.

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Signs of underwatering

The top 2 inches of medium are dry and pull away from the pot wall. The pot feels light. Leaf edges curl up and tips turn crisp. A wilted seedling recovers within 1 to 2 hours after a small watering.

Water quality and pH

Target pH 6.0 to 6.5 in soil and 5.5 to 6.0 in coco or hydro. Water temperature of 65 to 70 F (18 to 21 C) limits shock to young roots. Chlorine in tap water off-gasses in 24 hours. Chloramine does not. Use a carbon filter or bottled water if chloramine is a concern. Filtered or rainwater works without adjustment in most cases.

Room conditions that change the schedule

Air at 40 percent humidity pulls water from the medium faster than air at 65 percent. A fan pointed at the pot dries the surface in hours. A heat mat under a tray speeds evaporation. Check the medium each morning instead of following a fixed number of days.

Tools

• A 60 ml syringe or a squeeze bottle for exact amounts.
• A moisture meter, or a finger pushed 1 inch into the medium.
• A saucer to catch runoff, emptied after 15 minutes.

Seedling stage runs 2 to 3 weeks from the first set of true leaves. The exact schedule depends on pot size, medium, light, and humidity.