leafy green
EdibleRomaine / Cos Lettuce
Lactuca sativa var. longifolia
Considered non-toxic to cats and dogs (source: ASPCA (not specifically listed; generally regarded safe)).
Some direct sun — an east or west window, or a few hours of direct light.
Keep evenly moist — water when the top inch of soil is dry.
Forgiving and beginner-friendly.
Romaine is a crisp, upright lettuce that suits containers and tolerates modest light. You can grow it to a full head or harvest outer leaves continuously.
About Romaine / Cos Lettuce
Romaine, also called cos lettuce (Lactuca sativa var. longifolia), is a crisp, upright lettuce grown for its sturdy leaves. Cultivated lettuce traces back to the eastern Mediterranean and was a staple in ancient Egypt and Rome. It suits containers well and tolerates modest light, so a 4-litre pot on a medium-bright sill is enough. You have two options: grow it to a full upright head, or pick outer leaves cut-and-come-again for a longer supply. A leftover base will even resprout small leaves in water.
It takes medium light and even water, which makes it forgiving on a window that doesn't get full sun, and it grows readily under a grow light. Keep it cool to avoid bitterness and bolting, and give steady moisture so the leaves stay crisp and free of tip burn. The plant forms a head of about 0.2 to 0.3 m. A full head usually takes around 55 to 70 days.
What it’s like to grow
Romaine is easy and reads its needs clearly. Bitter leaves and a sudden flower stalk mean it got too warm, so keep it cool. Brown, scorched leaf tips come from uneven watering, fixed with steady moisture. It takes medium light, so a bright-ish window or a grow light covers it without full sun. It's non-toxic to cats and dogs. A reliable pick for a beginner who wants crisp salad leaves and the flexibility to either cut as they go or wait for a full head.
What to expect
First harvest in about 55–70 days. It’s forgiving, so it’s a good one to learn on. No sunny window? It also does fine under a clip-on grow light.
See what you’ll need to get started ↓♻ Regrow from scraps
Stand a leftover romaine base in shallow water and small new leaves regrow from the center.
Companions
Tips
- Pick outer leaves first to keep the center producing if you don’t want a full head.
- Keep it cool to avoid bitterness and bolting.
- Give even moisture so leaves stay crisp and tip-burn-free.
Common problems
- Bitter leaves and bolting in heat.
- Brown leaf-tip burn from uneven watering.
Common questions
Is Romaine / Cos Lettuce toxic to cats and dogs?
Romaine / Cos Lettuce is non-toxic to cats and dogs, which makes it a safe pick if you have pets. Source: ASPCA (not specifically listed; generally regarded safe).
How much light does Romaine / Cos Lettuce need?
Romaine / Cos Lettuce does best in medium, indirect light: near an east or west window, or a little back from a bright one. Direct midday sun can scorch it.
How often should I water Romaine / Cos Lettuce?
Water Romaine / Cos Lettuce when the top inch of soil feels dry, then let it drain. Aim for evenly moist, not soggy.
What temperature does Romaine / Cos Lettuce need?
Romaine / Cos Lettuce is happiest around 13–21 °C. It tolerates brief dips to about -2 °C, but cold drafts and sudden chills set it back.
How long does Romaine / Cos Lettuce take to grow?
Expect a first harvest about 55–70 days from sowing under good conditions. Forms an upright head over ~2 months, or harvest outer leaves cut-and-come-again for a longer supply.
Can I grow Romaine / Cos Lettuce without a sunny window?
Yes. Romaine / Cos Lettuce does well under an affordable clip-on grow light, so a bright window isn't essential.
How big does Romaine / Cos Lettuce get?
An upright leafy head ~0.2–0.3 m tall; space several with room to form heads.
How do I propagate Romaine / Cos Lettuce?
Sow seed thinly; lettuce is grown fresh each time and does not regrow fully from scraps.
What pests affect Romaine / Cos Lettuce?
Watch for aphids, whitefly, fungus gnats and thrips. Check new growth and the undersides of leaves often, and treat early with a rinse or insecticidal soap before they spread.
Is Romaine / Cos Lettuce easy to grow?
Yes. Romaine / Cos Lettuce is forgiving and one of the better plants to learn on.
Gear for Romaine / Cos Lettuce
Gear suggestions to get you started — general picks, not paid placements.
Pet-toxicity from the ASPCA. Care details are general guidance, not professional or veterinary advice; only eat plants you can positively identify as the edible plant and part described. Photo: Rainer Zenz, CC BY-SA 3.0, via Wikimedia Commons (CC-BY-SA). Care info last updated 2026-06-02.