Repotting guide

When & how to repot Romaine Lettuce (Lactuca sativa var. longifolia)

Also called Romaine Lettuce, Cos Lettuce, Roman Lettuce.

More about romaine lettuce

About Romaine Lettuce

Lactuca sativa var. longifolia · also called Romaine Lettuce, Cos Lettuce · edible

Romaine (cos) lettuce forms tall, upright heads of long, crisp, dark-green leaves with a prominent white midrib and robust, slightly bitter flavour. More heat-tolerant and bolt-resistant than butterhead types; the standard lettuce for Caesar salads. Matures in 60–75 days. Popular varieties include 'Little Gem', 'Parris Island Cos', and 'Fordhook'. Suitable for containers and cut-and-come-again harvesting.

Mature size: 25–40 cm tall; head 8–15 cm wide; 'Little Gem' a compact 20 cm form

Watch for — Aphid infestations: Lettuce root aphid (Pemphigus bursarius) and lettuce aphid (Nasonovia ribisnigri) colonise both roots and foliage. Wilting, distorted leaves, or black sooty mould indicate infestations. Use yellow sticky traps, introduce ladybird larvae, or apply neem oil spray. Grow resistant varieties such as 'Little Gem' or 'Chartwell'.

How to tell romaine lettuce needs repotting

Repotting on a calendar is less reliable than reading the plant. For romaine lettuce, watch for these signs:

Roots circling the bottom of the module or pot, or poking out of the drainage holes.
The seedling dries out within a day and growth has visibly stalled.
Roots are white and matted in a tight spiral when you tip the plant out.
It has outgrown its current container for the stage of the season — pot romaine lettuce on before it becomes hard root-bound.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot romaine lettuce

Pot on seedlings as they grow; not a perennial repot. Romaine Lettuceis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Tall, upright rosette forming an elongated, cylindrical head; leaves long, stiff, and cupped with prominent white midribs.

What size pot to step romaine lettuce up to

Pot romaine lettuce on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot romaine lettuce

Pot romaine lettuce on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.

Step-by-step: repotting romaine lettuce

Pot on before it is root-bound. Check romaine lettuce regularly; move it up as soon as roots reach the edge of the cell or pot, not after they have circled.
Step up one or two sizes. Choose the next container up — not a giant one. Cold, wet, unused soil around a small root system stalls seedlings.
Knock it out gently. Support the stem, tip the pot, and ease the rootball out without breaking it. A little teasing of circled roots at the base is fine.
Pot into rich mix. Set it into fresh fertile, well-drained, moisture-retentive loam at the same depth (tomatoes are the exception — they can go deeper to root along the stem).
Water in and grow on. Water well, keep it in good light, and resume feeding once it is established and growing again.

Aftercare

Water romaine lettuce in well and keep it in bright light; a freshly potted-on seedling can wilt for a day while roots settle, so do not overcompensate by drowning it. Do not fertilise for about 1 week — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for romaine lettuce

Romaine Lettuce wants fertile, well-drained, moisture-retentive loam. pH 6.0–7.0. Romaine's deeper root system (compared to butterhead) benefits from well-cultivated soil at least 20 cm deep. Incorporate compost before planting. In containers use a peat-free multipurpose compost with added perlite. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting romaine lettuce — frequently asked questions

How often should you repot romaine lettuce?

Pot on seedlings as they grow; not a perennial repot for romaine lettuce. Romaine Lettuce is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into fertile, well-drained, moisture-retentive loam so the roots never circle the cell, ending in a large final container. A root-bound transplant stalls and never fully recovers.

What size pot does romaine lettuce need?

When is the best time of year to repot romaine lettuce?

Can you put romaine lettuce straight into a much bigger pot?

No. Even a fast-growing romaine lettuce should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise romaine lettuce after repotting?

Not immediately. Wait about 1 week after repotting romaine lettuce. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.