Start feeding cannabis seedlings when the first true leaves are fully open and the seed's stored food is spent, usually 10 to 21 days after the sprout breaks the surface. Until that point the cotyledons and any nutrient charge already in the starting mix do the work. Feeding before the plant asks for it is the most common cause of stunted, burnt seedlings.
How to Prevent Nutrient Burn During Feeding
When should you feed a cannabis seedling for the first time?
Watch the plant, not the calendar. A seedling is ready for its first light feed when it shows three to four sets of true leaves, cotyledons start to yellow, and new growth looks slightly pale instead of deep green. Any one of those signals alone is a hint; two together is a green light.
- True leaves open: the serrated leaves, not the rounded seed leaves
- Cotyledons fading: the two round leaves yellow and drop
- Pale new growth: fresh tips lose that healthy dark tone
- Active roots: white roots reach the edge of the pot
Why do seedlings not need food at first?
The cotyledons carry enough stored energy to run the plant for the first week or two of life. Commercial seed-starting mixes also include a mild starter charge that covers the same window. Adding nutrients on top of that reserve is what burns the fine root hairs before they can recover.
Marijuana Fertilizer Schedule: Outdoor vs Indoor Comparison
How strong should the first feeding be?
Mix the first feed at one quarter of the label's adult strength, which lands around 0.4 to 0.6 EC or 200 to 300 ppm on a standard scale. Water until a little runs out the bottom so salts do not stack up in the root zone. Keep pH near 5.8 to 6.2 in coco and hydro, and 6.2 to 6.8 in peat or soil.
when to start feeding cannabis seedlings
Does the growing medium change the start date?
Yes, and it is the biggest variable after plant size. A hot, amended super soil can carry a seedling for four weeks, while an inert cube carries it for less than one.
- Seed-starting mix: first feed around day 14 to 21
- Amended super soil: water only for 3 to 4 weeks
- Coco coir: first feed around day 7 to 10
- Rockwool or inert media: feed from day 5 to 7
Has convenience changed when growers start feeding?
It has changed the default, not the biology. One-part nutrient lines, pre-charged seedling soils, and auto-dosing systems now push growers toward a fixed day on the bottle instead of a signal from the plant. Those shortcuts save time, yet the seedling still sets the schedule, and a fixed day ignores medium and root development.
What does overfeeding a seedling look like?
Leaves claw downward and turn glossy dark green, tips crisp to brown, and vertical growth stalls for a week or more. Flush with plain water at the correct pH and hold nutrients until new growth resumes. Seedlings recover, but the lost week never comes back.
What is a simple first-feed schedule?
- Water plain, pH-adjusted water for the first 10 to 14 days.
- Confirm at least three sets of true leaves before mixing anything.
- Feed at quarter strength once, then wait three to four days.
- Watch the response, then step up to half strength if growth stays green.
The date matters less than the signal. A seedling fed on day 12 in coco and a seedling fed on day 24 in living soil are both on time when the plant and the medium agree.