How-to Guide
When to Pot Up Seedlings
The short answer
The signal is true leaves. The first leaves a seedling unfolds are cotyledons (seed leaves, rounded and generic); the next pair are true leaves, shaped like the plant's real foliage. UNH Extension says the ideal time to transplant is when the first true leaves appear between the cotyledons, and Iowa State's guidance runs from first true leaves to the second pair, so the working window is roughly true-leaf stage while the plant is still small; transplanting small prevents the stunting and legginess that come from waiting.
The handling rule is absolute: by the leaves, not the stem. UNH is explicit that small seedlings should be held by their leaves because the stems are delicate and easily damaged, and the logic is brutal but simple: a seedling can spare a leaf, but a pinched stem is the whole plant's only plumbing.
Lift a clump gently, let it fall apart, tease out individuals, and set each in its own cell or pot in a pre-moistened mix at the same depth it grew before, firming gently and watering it in. From there the progression is cell to 3-to-4-inch pot as roots fill each container, then hardening off before the garden (see hardening-off-seedlings).
Reading the true-leaves signal
Cotyledons come first and look nothing like the plant; true leaves have the species' actual shape (a tomato's first true leaf already looks tomato-like). UNH's transplant timing is when the first true leaves appear between the cotyledons; Iowa State phrases it as when the first true leaves appear or when seedlings are large enough to handle, and notes some growers wait for the second pair.
Earlier-but-smaller beats later-but-bigger. UNH points out that transplanting while seedlings are still quite small prevents stunting and leggy growth, and small seedlings suffer less root damage because there is less root to damage. If seedlings are crowded shoulder to shoulder, the case for moving at first true leaves gets stronger; crowding stretches them fast (see thinning-seedlings-how-and-why for the alternative when you sowed thickly in place).
The potting-up procedure
Work with pre-moistened seed-starting or potting mix in the destination cells or pots, with a pencil-poked hole ready. Loosen and lift the seedlings from below with a knife, plant label, or wooden ladle (UNH's method), letting the root balls separate rather than tearing them apart.
Hold each seedling by a leaf, lower the roots into the hole, and set it at the same depth it was growing in the seed flat, per UNH. Firm the mix gently around the roots and water lightly to settle it; good root-to-mix contact matters more than pressure.
Give fresh transplants a day or two of gentler light while they re-anchor, then return them to full growing light so they don't stretch. If any flop, mist and shade before assuming the worst; true-leaf-stage seedlings recover from a surprising amount.
The cell-to-pot progression
From a community tray, the first stop is an individual cell or small pot; from a cell, the next stop (for plants that stay indoors for weeks more, like tomatoes and peppers) is a 3-to-4-inch pot once roots wrap the cell's mix. Each move goes up only one modest size so the roots can occupy the new volume before it sours.
Once seedlings live in real potting mix, feeding enters the picture; see when-to-start-fertilizing-seedlings for timing and dilution, and starting-seeds-indoors for the full upstream process.
The final 'potting up' is the garden, and it has its own ramp: UNH's hardening-off protocol runs one to two weeks of gradually increased outdoor exposure. Details at hardening-off-seedlings.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- UNH Extension — Starting Plants From Seed [fact sheet] — Ideal transplant time is when the first true leaves appear between the cotyledons ('seed' leaves); transplant while seedlings are quite small to prevent stunting and leggy growth; handle small seedlings by their leaves, not their delicate stems; dig up small plants with a knife or wooden pot ladle, let the clump fall apart, pick out individual plants, and set each at the same depth it grew in the seed flat; harden off over 1-2 weeks before outdoor planting
- Iowa State University Extension Yard and Garden — How to Successfully Start Seed Indoors — Transplant seedlings sown in furrows or flats into individual containers or cell packs when the first true leaves appear or when large enough to handle; some guidance waits until the second pair of true leaves