The Seedling Weeks

The seedling stage runs roughly from the day the sprout breaks the surface to the day the plant has four or five sets of real leaves, usually two to three weeks. It is the stage where most first grows go sideways.

Not because it is technically hard. Because it is boring and the plant barely moves, so people start doing things. They water it because it looks thirsty. They feed it because the leaves are pale. They drop the light closer because growth seems slow. Every one of those is a way to hurt a seedling.

Your entire job for three weeks is to hold a stable environment and keep your hands off the pot. That is genuinely it.

What you should be seeing#

The first two leaves are round and smooth. Those are cotyledons, and they are not really leaves. They are the seed's stored food, and they will yellow and fall off in a few weeks. That is supposed to happen.

The first true leaves come next, usually single bladed. Then a set with three blades, then five, then seven. By the time you have four or five nodes with five and seven blade leaves, the seedling stage is over and the plant is in vegetative growth.

Week	What it looks like	What you do
1	Sprout up, two round cotyledons, maybe a first single blade leaf	Mist or water a small ring. No nutrients.
2	Two to three nodes, three blade leaves, roots filling out below	Water slightly wider, still no nutrients
3	Three to five nodes, five blade leaves, visible daily growth	First real watering of the full pot. Lower the light.

Growth in week one looks like nothing is happening. That is because it mostly is not, above ground. The plant is building roots. Week three is when the top growth suddenly takes off, and it takes off because of root work you could not see.

Environment targets#

Setting	Seedling target
Temperature, lights on	70 to 78F
Temperature, lights off	No more than 10F below the day temp
Humidity	65 to 70%
Light schedule	18 hours on, 6 hours off
Light height	18 to 24 inches above the plant
Light intensity	25 to 50% on the dimmer
Airflow	Gentle. Leaves flutter, they do not thrash.

Seedlings like it more humid than you would expect, because their root system is tiny and they take in a lot of water through the leaves. If your tent sits at 40 percent, a cheap humidifier or a clear dome over the pot for the first week will help.

Watering a seedling#

This is the one that kills plants.

A seedling has a root ball the size of a shot glass sitting in a three or five gallon pot. If you soak the whole pot, most of that water is nowhere near the roots and it just sits there. Soil that stays saturated has no oxygen in it, the roots suffocate, and you get droopy leaves that look exactly like thirst. So you water again. That is how people drown seedlings while believing they are rescuing them.

Instead, water a small ring about two inches out from the stem, roughly a cup at a time in week one. Each time you water, widen the ring a little. This does two things: it keeps the rest of the pot from going swampy, and it encourages roots to grow outward toward the moisture.

By week three the root system is big enough to handle watering the full pot surface, and you can switch to the normal routine.

The soil should go from damp to nearly dry between waterings. Lift the pot. A pot that feels heavy does not need water regardless of what the surface looks like.

Do not feed it#

If you bought pre-amended organic potting soil, it already has three to four weeks of food in it. Adding nutrients to a seedling in that soil is the fastest way to burn it, and the symptoms of nutrient burn look a lot like the symptoms of deficiency, which sends people into a spiral of adding more.

Pale green new growth in week one and two is normal. Wait. Around week three or four, when the plant is actively drinking and the lower leaves start to fade, that is when feeding becomes a real conversation.

Plain water for the first three weeks. If your tap water is hard, that is fine. Aim for a pH in the 6.0 to 7.0 range, which most tap water is already close to.

Fixing a stretchy seedling#

If your seedling comes up with a long thin stem and the leaves are three inches above the soil, the light is too far away or too dim. The plant is reaching.

Two fixes, and use both. Lower the light or turn up the intensity, and then bury the extra stem. Cannabis will root from a buried stem. Gently add soil up to just below the cotyledons, or transplant the seedling deeper into a new pot. Also get a fan moving air across it, because stem strength comes from movement.

A leggy seedling that gets fixed in week one is fine. A leggy seedling left alone becomes a plant that falls over under the weight of its own buds in week nine.

Pot size and transplanting#

You have two reasonable options.

Plant straight into the final three or five gallon pot. Simplest, no transplant shock, and the only requirement is that you water in a small ring as described above so the pot does not stay soaked.

Or start in a plastic cup or one gallon pot and move up around week three. The advantage is that a small container dries out faster, which makes overwatering harder. The downside is one transplant, which means one chance to damage roots.

Either is fine for a photoperiod. If you are running an autoflower, go straight into the final pot and do not transplant at all.

When you do transplant, water the plant the day before so the root ball holds together, then tip the pot sideways and let it slide out rather than pulling on the stem.

Knowing when this stage ended#

Once you have four or five nodes, leaves with five and seven blades, and the plant is visibly bigger every morning, the seedling stage is behind you. Light can come down to 12 to 18 inches, intensity can go up, and the plant will start drinking real volumes of water.

Which makes the next thing worth getting right: how much water, and how often.