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Most lettuce problems have more than one possible cause, so check the plant, soil moisture, drainage and recent weather before choosing a fix. Heat can make lettuce bitter or slow to form heads; uneven watering can damage young leaves; and holes may point to pests rather than disease. Use the symptom guide below to narrow down what is happening and what to do next.
1. Lettuce bolts and turns bitter
Bolting is the shift from leaf growth to flowering. Heat, long days and stress can prompt it. As flowering begins, leaves often become tougher and more bitter. The Royal Horticultural Society notes that all lettuces eventually flower if left long enough.
What to do
- Grow lettuce as a cool-season crop and sow so plants mature before the hottest part of the season; exact planting dates depend on local conditions. See University of Minnesota Extension’s lettuce guide and University of Maryland Extension’s home-garden guide.
- Choose a cultivar described as slow to bolt or suited to your season. A slow-bolting variety can reduce risk, but does not prevent eventual flowering.
- Keep soil moisture steady and provide light shade during hot periods. Shade can reduce heat stress, but it will not reverse bolting.
- Harvest spring crops as soon as leaves or heads are usable. Once a plant is flowering, harvest what remains in acceptable condition or replace it rather than expecting it to return to leaf growth. The RHS growing guide advises not delaying harvest once plants have formed a good heart.
2. Brown leaf edges or spots: possible tipburn
Tipburn appears as brown margins or spots on young, rapidly growing leaves. It may be concealed inside a head until harvest. Utah State University Extension describes tipburn as a localized calcium shortage in growing tissue; it does not necessarily mean the soil lacks calcium. Drought followed by renewed moisture, heat, excess nitrogen, flooding and root injury can all contribute.
What to do
- Keep moisture more even through the root zone, avoiding both dry spells and waterlogged soil.
- Avoid excessive nitrogen and take care not to damage roots while cultivating.
- Trim away damaged parts; sound portions can still be used. Do not add calcium automatically: first address moisture, heat and root conditions. See Utah State University Extension’s guide to physiological problems.
3. Lettuce seeds do not germinate
Insufficient moisture and old seed are common possibilities. Some white-seeded types need light to germinate, so covering them too deeply can prevent emergence. Soil temperature matters too: the University of California Statewide IPM Program gives an optimum germination range of 68–77°F (20–25°C) and says germination is inhibited above 86°F (30°C). These are source-specific growing guidelines, not a guarantee for every seed lot.
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What to do
- Check the seed packet and, if the seed is old or storage conditions are uncertain, try a fresh packet.
- Prepare a fine seedbed, sow in cooler conditions when needed, and keep it evenly moist while seeds germinate.
- For a light-requiring seed type, press seeds into contact with the soil rather than burying them. Illinois Extension covers this and other causes in “Why didn’t my lettuce seeds germinate?”. Temperature guidance is from the UC Statewide IPM Program.
4. Holes, missing seedlings or distorted leaves: inspect for pests
Different damage patterns can point to different pests. Aphids often cluster underneath leaves; slugs and snails leave holes; flea beetles make many small, round holes; and cutworms can sever seedlings at the base. Inspect the plant and nearby soil rather than treating all damage the same way.
What to do
- Look under leaves for aphids and check around the plant after dark or in damp hiding places for slugs and snails.
- If seedlings are missing or cut through at soil level, inspect the base and surrounding soil for cutworms.
- Remove weeds that can shelter pests. A suitable row cover can protect young plants where appropriate, but check local extension or integrated pest management guidance before selecting controls. Identification and control options are described by RHS and University of Minnesota Extension.
5. Soft decay, fuzzy growth or leaf spots: consider disease and rot
Soft tissue decay with fuzzy grey growth can be grey mould, according to the RHS. Downy mildew can produce yellow patches with fuzzy white growth. Wet foliage and poorly drained soil can also increase the risk of leaf and root rots. These symptoms differ from tipburn, which is physiological rather than an infectious disease.
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What to do
- Improve drainage and airflow, and avoid keeping foliage wet for long periods where feasible.
- Remove badly affected plants. If the symptoms do not clearly match a known problem or continue to spread, seek a diagnosis from your local extension service; disease appearance and recommended management can vary by location.
See the RHS guide to lettuce problems and the UC Statewide IPM Program’s growing guidance.
6. Wilting, slow growth or poor-quality leaves: check heat and water
Lettuce is a cool-season crop with shallow roots. Too little or irregular water can slow growth, while overwatering—especially in heavy soil—can encourage soft growth, disease and leaf-margin damage. Both soil moisture and drainage matter.
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- Specially formulated with micronutrients to help plants grow strong and produce more fruits and vegetables versus unfed plants
- Calcium helps form stronger cell walls, producing better quality and longer-lasting fruits and vegetables. Plus, it helps prevent disorders in edible crops commonly associated with calcium deficiency.
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What to do
- Water enough to keep the root zone moist, but make sure excess water drains away. Mulch can help reduce moisture loss.
- For summer seedlings, the UC Statewide IPM Program recommends protection with 50% shade cloth or two layers of floating row cover until plants have about six leaves. This is targeted protection for young plants, not a cure for bolting.
- Use shade cloth to reduce direct sun and heat; floating row cover serves different purposes, including season extension and some pest protection. For local growing guidance, consult Illinois Extension and Maryland Extension.
7. Heads are loose or disappointing
High temperatures can produce loose, fluffy heads and tipburn. A variety poorly suited to the season, crowded plants, inconsistent moisture or harvesting too late can also reduce quality. Match the lettuce type and cultivar to your growing conditions, then follow the spacing and maturity guidance for that variety.
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What to do
- Choose among leaf, cos (romaine), butterhead and crisphead types based on the season and the space available; check local advice for cultivars suited to your climate.
- Give plants the spacing recommended for their type and keep moisture consistent.
- Harvest at maturity. Some loose-leaf lettuce may be ready to pick in 4–6 weeks, according to the RHS; timing varies by variety and growing conditions.
- Do not add fertilizer by default. The RHS says lettuce usually does not need feeding in ordinary garden conditions. See RHS growing guidance and the UC Statewide IPM Program.
Choose the fix from the symptom
| What you see | Check first | Useful first response |
|---|---|---|
| Bitter leaves or a flower stalk | Heat, long days, plant age and moisture stress | Harvest usable leaves or replace a flowering plant; plan the next crop for cooler conditions. |
| Brown edges or spots inside young leaves | Recent drying and rewatering, heat, excess nitrogen or root disturbance | Steady moisture; avoid adding calcium without diagnosing conditions. |
| No seedlings | Seed age, moisture, sowing depth and soil temperature | Keep the seedbed moist; press light-requiring seed into the soil surface. |
| Holes or severed seedlings | Undersides of leaves, plant bases and nearby hiding places | Identify the pest before choosing a control; consider suitable row cover for young plants. |
| Soft or fuzzy growth, yellow patches | Wet foliage, poor drainage and symptom pattern | Improve drainage and airflow; remove badly affected plants and seek local diagnosis if uncertain. |
| Wilting or slow growth | Root-zone moisture, drainage and heat | Maintain moisture without waterlogging; shade vulnerable summer seedlings. |
| Loose heads | Heat, cultivar, spacing, moisture and harvest timing | Match variety and spacing to the season; harvest at maturity. |
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