Seeds, germination and seedlings

What this is

This paper takes a complete beginner from a dry cannabis seed to a healthy two-to-three-week-old seedling, defining every term along the way. A seed is a tiny dormant plant in a protective shell, waiting for the right cues to wake up. Germination is the act of waking it. A seedling is the baby plant in its first weeks of life.

Get these early stages right and the rest of the grow is far easier, because most fatal mistakes happen in the first 21 days. Read this before buying or planting anything.

Key terms, defined once

Before the how-to, here is the small vocabulary the rest of this paper relies on. You do not need to memorise it, each term comes back in context.

Inside a seed, and how to judge a good one

A cannabis seed is a complete dormant plant. A tough seed coat protects an embryo that already contains a taproot, two cotyledons and a tiny shoot, plus stored food to fuel the first days of growth before the plant can feed itself.

Quality is partly visible. Mature, viable seeds are firm, dark brown, and often mottled with a ‘tiger-stripe’ pattern, and they do not crush under gentle finger pressure. Pale white, yellow, or light-green seeds were usually harvested too early and tend to sprout poorly or produce weak plants.^[1]

Fresh seeds stored cool, dark and dry stay viable for years, but germination rate falls as seeds age and their stored oils break down.^[2] A sealed container in the fridge is a good home for spares.

Feminised, regular and autoflower: which seed to buy

There are three seed types and the choice shapes your whole grow. Regular seeds produce roughly half male and half female plants. Only females make the flower (the ‘bud’) most growers want, so males are usually removed.

Feminised seeds are bred to produce almost only female plants, removing the guesswork and wasted effort. They are made by inducing a female plant to make pollen (using treatments such as colloidal silver), so the resulting seeds carry only female genetics.^[4][5]

Autoflower seeds carry Cannabis ruderalis genetics that make the plant flower automatically after about 2-4 weeks regardless of the light schedule, finishing in roughly 60-90 days from sprout.^[6] Photoperiod plants (regular and feminised) only flower when the daily light drops to about 12 hours.^[7]

Three ways to germinate, and why

Germination just means giving the seed three things: water, warmth and darkness. The embryo swells, drinks, and pushes the taproot out through the seed coat. There are three common ways to deliver those three things.

The paper-towel method (seeds between damp paper towels, sandwiched between two plates) is the most popular because you can watch the taproot appear, and it reports near-99% success when conditions are controlled.^[2] Its one risk is damaging the fragile root when you move the seed to its pot.

The conditions seeds need, and what to expect when

Seeds are sensitive to their environment. Three settings matter: temperature, moisture and light. Get all three in range and most viable seeds sprout on their own.

Hold temperature at a steady 21-25C (70-77F). Cooler slows germination, and warmer or fluctuating temperatures cause outright failures.^[3] Keep the medium or towel damp like a wrung-out sponge, never waterlogged, and keep seeds in darkness until they sprout.

Seedling care: the first two to three weeks

The newborn seedling has almost no roots, so it drinks largely through its leaves. That means it needs high humidity, typically 65-80% RH (a VPD of about 0.4-0.8 kPa), often using a humidity dome or a vented clear bag for the first 7-10 days.^[9] VPD (vapour pressure deficit) is just a measure of how thirsty the air is. Lower means more humid.

Keep light gentle: roughly 100-200 PPFD in the first week, rising to 200-300 PPFD by week two (a DLI near 10-15), with LEDs kept well back to avoid stretch or burn.^[8] PPFD is the amount of usable light hitting the plant right now. DLI is the total it receives over a day.

Do not feed at first. The cotyledons supply the plant's food. Start a weak nutrient solution at about 25% strength (EC roughly 0.3-0.8 mS/cm) only once the first true leaves appear, around weeks 2-3. Water sparingly around the base and let the surface dry slightly between waterings so roots reach down to find moisture.

Damping-off and other common failures

The most lethal seedling disease is damping-off, caused by soil fungi such as Pythium, Fusarium and Rhizoctonia. A previously healthy seedling suddenly pinches, blackens and topples at the soil line, and it is almost always fatal once it strikes.^[10]

The dominant cause is overwatering combined with too-high humidity and poor airflow, so prevention beats cure. Use fresh sterile medium, water sparingly, add gentle air circulation, and drop humidity toward 40-50% once true leaves appear.^[11]

Realistic expectations

Even with good seeds and care, not every seed sprouts. Fresh quality feminised seed often runs well above 90% germination, but a dud or two is normal and not a sign you did something wrong.^[1]

Budget about 3-4 weeks from planting to a sturdy seedling with several sets of true leaves before the plant truly takes off into vegetative growth. Germinate one or two extra seeds as insurance, expect to lose the occasional seedling, and resist the two biggest temptations: overwatering and feeding too early.

Slow and gentle wins these first weeks. Once your seedling is established, look at light acclimation to ramp it up safely, and keep mould risk in mind as humidity comes down. If you would rather skip seeds entirely next time, cloning gives you an exact copy of a plant you already trust.