Troubleshooting
Cos Romaine Lettuce problems — and how to fix them
Cos Romaine Lettuce (Lactuca sativa var. longifolia 'Cos') is generally forgiving once you match its basics, but a few issues come up again and again. Here is what each one looks like, why it happens, and the fix.
Tip-burn
Brown, scorched leaf edges inside the head come from calcium not reaching fast-growing tips, usually after uneven watering or heat. Keep moisture steady and avoid forcing soft, rapid growth.
Bolting
Heat and long days trigger early flowering and bitterness. Cos is fairly bolt-resistant, but spring and autumn sowings plus consistent watering give the best, sweetest hearts.
Bottom rot and grey mould
Dense heads in wet, crowded beds rot from the base or develop fuzzy mould. Space heads, water at the base, and ensure good drainage and airflow.
Slugs in the heart
Molluscs hide deep inside the upright leaves where they are hard to reach. Use barriers and traps early, and clear debris from around the plants.
Prevent cos romaine lettuce problems before they start
Most cos romaine lettuce issues are care-mismatch, not bad luck. Dial in the basics:
- Common lettuce problems — the species this cultivar belongs to
- What's wrong with my plant? — the diagnosis apps compared
- Cos Romaine Lettuce watering schedule
- Cos Romaine Lettuce light requirements
- Best soil mix for cos romaine lettuce
- Cos Romaine Lettuce temperature & humidity
- Full cos romaine lettuce care guide
Looking for cos romaine lettuce in general rather than its problems? Read the full cos romaine lettuce care guide — light, water, soil and feeding.
Cos Romaine Lettuce problems — FAQ
Why is my cos romaine lettuce tip-burn?
Brown, scorched leaf edges inside the head come from calcium not reaching fast-growing tips, usually after uneven watering or heat. Keep moisture steady and avoid forcing soft, rapid growth.
Why is my cos romaine lettuce bolting?
Heat and long days trigger early flowering and bitterness. Cos is fairly bolt-resistant, but spring and autumn sowings plus consistent watering give the best, sweetest hearts.
Why is my cos romaine lettuce bottom rot and grey mould?
Dense heads in wet, crowded beds rot from the base or develop fuzzy mould. Space heads, water at the base, and ensure good drainage and airflow.
Why is my cos romaine lettuce slugs in the heart?
Molluscs hide deep inside the upright leaves where they are hard to reach. Use barriers and traps early, and clear debris from around the plants.