A seedling is the young plant between emergence and the start of vigorous vegetative growth. It begins with two rounded seed leaves (cotyledons), then produces true leaves with one, then three, then five leaflets. Most growers call it a seedling for roughly the first 2-3 weeks, until it has 3-4 nodes and is growing quickly.
In practice
Seedlings have small roots and little stored water, so they are easy to drown and easy to scorch. Typical targets are gentle light (about 200-400 µmol/m²/s PPFD), 22-26 °C (72-79 °F), fairly high humidity (about 60-70% RH) and light watering in a small volume around the stem rather than a full soak of a big pot. Little or no feed is needed for the first week or two in most pre-fertilised mixes; in inert media a weak solution (about 0.4-0.8 mS/cm) is common.
The classic beginner fault is overwatering a seedling in a large, cold, wet pot.
Don't confuse with
- Clone (rooted cutting): also small and young, but grown from a cutting, with no taproot or cotyledons.
- Stretchy seedling: a seedling with long, weak stem; usually too little light, not a separate stage.
One of the two rounded seed leaves packed in the embryo that open first after germination and feed the seedling until the true leaves take over.The first leaves produced by the shoot tip after the cotyledons, with the plant's characteristic serrated leaflets.One of the separate serrated blades that make up a palmate cannabis leaf; a mature fan leaf typically has five to eleven leaflets.Photosynthetic photon flux density: the number of PAR photons landing on one square metre each second, in µmol/m²/s; the standard measure of light intensity at the canopy.Relative humidity is the water vapour in air as a percentage of what it could hold at that temperature, so the same RH dries plants differently at different temperatures.mS/cm (millisiemens per centimetre) is the standard unit of EC for nutrient solutions; 1 mS/cm equals 1 dS/m and 1,000 µS/cm.Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.The dominant primary root that grows straight down from the radicle of a seed-grown plant, with lateral roots branching from it.Germination is the stage where a viable seed absorbs water, splits its shell and pushes out a root (radicle), usually within 1-7 days at 20-30 °C.The collapse of seedlings or cuttings when soil-borne pathogens such as Pythium, Rhizoctonia solani and Fusarium rot the stem at the soil line.Hardening off is gradually exposing plants raised indoors or under a dome to harsher conditions, such as sun, wind and lower humidity, so they adapt without shock.Veg time is how long a photoperiod plant is kept in vegetative growth under long days before being flipped to flower, which largely sets its final size.
