When you harvest will depend on the season and the variety you’ve planted. Ask your seedling nursery or the seed company how many days the variety normally takes from seeding or transplanting to harvest.
When to harvest Cos and Iceberg lettuce
About a week before your estimated harvest date, walk through your field and pick out a few lettuce heads that look ready. Cut them in half and check how closely leaves are packed in the head. If five or six heads out of ten are tightly packed inside, the crop is ready for harvest.
If a few of the heads you have cut open have a core - that is, they are starting to elongate - start harvesting immediately, before the crop runs to seed.
Consider recent weather patterns and research the lifecycle of the lettuce variety you’ve planted.
- If the weather is warmer than normal, your lettuce will be ready a few days earlier.
- In cold weather it might take six or seven days longer before being ready to harvest.
Ideally, the whole planting is cut in one pass, but sometimes two cuts several days apart, may be necessary to maximise head quality.
Heads are not filling out properly
If the heads aren't filling out or sizing up properly, you may have selected the wrong variety for that time of year, you may be under watering or not applied sufficient nutrition to the crop. Some winter varieties need cold weather to heart-up properly and form a solid head.
Splitting or bolting (run to seed)
Lettuce that is split open or bolted has started to flower. If lettuce is showing signs of splitting, bolting or stress, such as brown leaf margins or tipburn, there are multiple explanations:
- you’re not harvesting early enough
- the lettuce may be a cool-weather variety planted out of season or the weather has been much warmer than normal
- too much nitrogen can cause 'fluffy' heads, where the heads are being grown too quickly and aren’t able to form a head before bolting.
- stunted lettuce may look like the heads are not filling out.
- if only some of the lettuce is bolting, the block may be variable in its maturity. You may be stressing the crop.
- if one area of the crop is better than another, there could be an issue with nutrition or irrigation.
Always continuously check your general management practices, irrigation, fertiliser and planting practices.