Short answer. Pot up when roots reach the sides and bottom of the container but before they circle (lift the plant out: you should see white roots at the edge holding the ball together). Typical path: plug → 1–3 L (0.25–0.8 US gal) at 2–3 weeks → final pot 2–4 weeks before the flip. Move the root ball intact into pre-moistened medium of the same type and pH, water in lightly, and give it 2–4 easy days. Autoflowers: sow straight into the final pot. This is Grower practice consistent with general horticulture [1][2].
Why pot up at all
A small container wets and dries evenly around a small root ball. A giant pot around a seedling stays wet in the zone with no roots (low air, high disease risk [3]). Potting up keeps the moisture cycle matched to root size [2].
Numbers that matter
| Step | Container | Typical timing |
|---|---|---|
| Seedling/clone | Plug, cube, 0.25–0.5 L cup | Until 2–4 true-leaf nodes |
| First up-pot | 1–3 L | 2–3 weeks from sprout |
| Final pot (photoperiod) | 11–25 L soil/coco; slab/block for rockwool | 2–4 weeks before flip |
| Autoflower | 11–15 L final | Sow direct into the final pot; don't transplant |
| Ratio per step | ~2–4× volume | Bigger jumps = slower drying |
House position: pot size is a trade-off. Bigger pots give bigger yields, within reason; across many crops, bigger rooting volume generally means bigger plants (Poorter et al. 2012 meta-analysis). But root volume isn't the whole story: the founder has grown a QP+ (4 oz+, ~115 g+) from a 16 oz (~0.5 L) cup. If you push water and nutrients hard enough (high-frequency fertigation), big things come in small packages. Small pots need more frequent feeding and watering and leave less margin for error; big pots are more forgiving but dry slower. Match the pot to how often you can irrigate.
How to do it
- Water the plant lightly the day before so the root ball holds together.
- Pre-moisten the new medium to "wrung sponge" and pH-correct it (soil 6.2–6.8; coco 5.8–6.2).
- Make a hole the size of the old container (use an empty pot as a mould).
- Tip, support the stem between fingers, slide the ball out, set it in. Stretched seedlings can be set deeper in soil or coco (Grower practice).
- Firm gently; water in with a small amount of mild solution.
- Lower light ~10–20 % and keep RH a little higher for 2–3 days.
- Rockwool: place the block on the slab; irrigate the block until roots enter the slab.
How to recognise transplant shock
Drooping or slow growth for 2–5 days, mild leaf curl. Lasting longer, check for: root damage, waterlogged new medium, pH mismatch, or a hot, bright light right after the move.
Common mistakes
- Breaking the root ball.
- Transplanting into dry or soaking medium.
- Transplanting in flower (a late emergency pot-up can work; expect a stall).
- Transplanting autoflowers at all. Any setback costs an auto time on its fixed clock, and the founder finds the auto taproot reacts badly to it; sow into the final pot (house position).
Evidence
Container physics is Established [2]. Transplant timing and handling is Grower practice aligned with extension seedling guidance [1][3].
