Tip burn

Brown, dead leaf edges deep in the heart of a lettuce or cabbage. Calcium never reached those leaves — which is a plumbing failure, not a shortage in the soil.

Disorder Serious Doesn't spread

What you'll see

Leaf margins browned, dried and papery on the young inner leaves of a lettuce or cabbage heart.
Outer leaves perfectly sound, which is what distinguishes this from scorch or drought.
The damage only visible when the head is cut open, so a crop can look faultless in the row.
Soft rot following into the dead margins and spoiling the head.
On strawberry, blackened tips on the newest unfolding leaves; on cabbage, an internal browning of the inner leaves.

Why it happens

Calcium moves in the transpiration stream, and the tightly wrapped inner leaves of a head barely transpire at all — so calcium goes to the outer leaves that are losing water and never reaches the inside. Almost every case is on soil with plenty of calcium in it. What causes it is anything that makes the plant grow fast or transpire unevenly: heat, a rain after drought, high humidity, or a heavy nitrogen feed.

Hot weather, rapid growth, high humidity at night, erratic watering, and heavy nitrogen or potassium feeding, which competes with calcium uptake. Hearting lettuce, cabbage and Chinese cabbage in a hot spell are the classic cases.

Treating it

There is no cure for a head already affected. Cut away the browned margins and use the rest.
Harvest the crop promptly rather than leaving it to size up, since the damage worsens and rot follows.
Water evenly and mulch for the rest of the row.
Stop the nitrogen feed.
Do not add lime or a calcium supplement, which does nothing for this — the calcium is already there.

Keeping it away

Water steadily and mulch so growth is even rather than a stop-start rush.
Feed moderately; forced, sappy growth is the underlying cause more often than anything else.
Grow tip-burn-resistant lettuce cultivars, which are widely available and genuinely differ.
Time hearting crops to mature outside the hottest weeks of summer.
Give summer lettuce a little afternoon shade and good air movement at night.

Who gets it

Lettuce, cabbage, Chinese cabbage and Brussels sprouts, and the new leaves of strawberries.