Gadenin日本語Get the appHeading is decided by the number of outer leaves
Before the inner leaves start folding in, the plant has to have built about twenty outer leaves. The sugars those outer leaves produce drive a sudden burst of inner leaves which, with nowhere to go, fold over each other. That is what a head is. A plant with small outer leaves will not do it whatever the conditions.
So the outcome is decided in the three weeks after planting rather than during heading itself. Run short of feed or water, crowd the plants, or shade them in that window and the plant has already lost the ability to head.
- Feed two weeks after planting This is when the outer leaves are extending, so scatter a light dressing around the plant and work it in. Leave it later and the plant reaches heading with small outer leaves.
- Do not crowd them Heading lettuce needs twelve inches (30 cm). At ten inches the outer leaves overlap and compete for light. When the leaf tips touch the neighbor it is already too tight, so pick alternate plants early.
- Keep the moisture even Letting it dry hard and then soaking it stops the outer leaves extending. Check the surface with a finger and water when it is dry, on a steady rhythm.
Working out why it did not head
The shape of the plant tells you most of it. Whether the leaves spread wide and large, whether the whole plant stayed small, or whether a stem is rising from the middle, each points somewhere different.
| The plant | Likely cause | Change next time |
|---|---|---|
| Big outer leaves but no head | Heat during heading | Sow earlier so heading falls in cool weather |
| The whole plant stayed small | Not enough outer leaf, underfed | Feed reliably two weeks after planting |
| A stem rising from the center | Bolting | Use a bolt resistant variety, avoid late spring sowing |
| Yellow leaves, lower leaves dying | Root damage from wet soil | Raise the bed and fix the drainage |
Heat and long days make it bolt
Above 77F (25C) for a run of days a lettuce forms a flower bud, and lengthening days push it further. Once a stem starts rising from the center and the leaves space out along it, no amount of waiting brings a head back.
A spring crop that runs into early summer meets this head on. An autumn crop is moving the other way, so there the problem is a head that never fills rather than bolting. Each season has its own characteristic failure.
- Bring the sowing forward Sow the spring crop at the earliest end of the window and design it to be finished before the heat. A week earlier absorbs several degrees at the far end.
- Shade to cool the soil If heat arrives just before harvest, put shade netting over the bed. Straw around the plants slows the soil warming too, and buys you a few days.
- Cut it as soon as it starts Once the center begins to rise, quality only falls. Cut it that day even if the head is loose, trim the outer leaves and use it.
Bitterness comes from the stem
The bitterness in lettuce is in the milky sap that runs from a cut. Once bolting starts the stem extends and there is more of that sap, and the leaves turn bitter with it. The same variety picked young has almost none of it.
A bitter plant is much less noticeable cooked, so it is not wasted: it goes into a stir fry or a soup. If you want it raw, the answer is to design the crop so you cut before bitterness arrives.
- Cut in the morning By the middle of the day the plant is warm and more sap runs from the cut. Cutting early gives better flavor and better keeping.
- Do not put off cutting The longer a firm head stands, the more the stem extends and the more bitter it gets. Once it feels firm, plan to cut within a few days.
- Cook the bitter ones Trim the outer leaves and the core, shred it and fry it in oil or drop it into soup. Heat and fat take most of the bitterness out.
Too much nitrogen and water also stops heading
Underfed, the outer leaves never get big. Overfed with nitrogen, the leaves get big but the center never closes. A good base dressing and a restrained feed afterwards is the pattern that works for heading lettuce.
| Stage | Feed and water | Purpose |
|---|---|---|
| Before planting | Compost and base fertilizer across the bed | Build the ground for outer leaves |
| Two weeks after planting | A light feed | Get to about twenty outer leaves |
| Heading starts | Stop feeding | Switch to tightening the leaves |
| Week before cutting | Water sparingly | Avoid rot and splitting |
Leaf color going past deep green into blue-black means too much nitrogen. Stop feeding and water less often.
What to do with a plant that never headed
A lettuce that did not head is still perfectly good as leaves. Before you pull it, pick from the outside and you will get several weeks of cutting from it. Pull the whole plant only when you need the ground.
- Pick from the outside Leave four or five leaves at the center and fold the outer leaves sideways to snap them off. As long as the center is there, new leaves keep coming.
- Write down what happened Record the sowing date, the planting date and the date you gave up on heading. Next year the adjustment becomes a number of days rather than a guess.
- Clear the bed promptly A bolted plant left standing becomes a source of aphids. Unless you want the flowers, pull it and take it off the plot.