Fertilising guide

How to fertilise Iceberg Lettuce (Lactuca sativa var. capitata 'Iceberg')— schedule & NPK

Also called iceberg lettuce, crisphead lettuce.

More about iceberg lettuce

About Iceberg Lettuce

Lactuca sativa var. capitata 'Iceberg' · also called iceberg lettuce, crisphead lettuce · edible

Iceberg is a crisphead lettuce forming a large, dense, round head of pale, very crunchy, mild leaves. It is the most demanding lettuce type, needing steady cool conditions, even moisture and space, and matures in about 70-85 days. Reliable cool-season cropping makes it popular, though it bolts readily in heat.

Growth habit: Crisphead annual forming a single large, tight, rounded head; bolts into a tall central flower stalk when heat- or moisture-stressed.

Watch for — Tip burn: Brown, scorched margins inside the head from calcium not reaching fast-growing tissue under heat or uneven watering. Maintain steady moisture and avoid heat stress.

What fertiliser iceberg lettuce actually wants — and why

Iceberg Lettuce is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.

For the language behind the three numbers on the bottle — what nitrogen, phosphorus and potassium each do — see the NPK ratio explained entry. The short version for iceberg lettuce: match the feed to the job the plant is doing right now, not to a generic “plant food” on the shelf.

How often to feed iceberg lettuce, and which months

Feeding only earns its keep while the plant is in active growth and can use the nutrients — pour feed into a dormant or low-light plant and it simply builds up as root-burning salt. For iceberg lettuce:

Feed lightly with a balanced fertiliser early to support steady growth and firm heading; avoid heavy nitrogen, which produces soft heads that are slow to firm and prone to rot. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).

The dormant-season rule matters more than the exact interval: skip feeding entirely when iceberg lettuce is resting. For the wider context on indoor feeding rhythms across the seasons, the houseplant fertiliser schedule walks through the year month by month.

What strength to mix for iceberg lettuce

Use the vegetable-feed label rate for iceberg lettuce. Steady availability matters more than a strong dose — a check in growth makes leaves tough and can trigger bolting.

Feeding always goes onto already-damp soil, never dry roots — water iceberg lettuce first if the soil is dry, then apply the diluted feed. The companion question is when to water at all, covered in the iceberg lettuce watering schedule.

Signs you are over-feeding iceberg lettuce

Over-feeding is far more common — and more damaging — than under-feeding for most plants. The classic tells for iceberg lettuce:

Very soft, floppy, dark-green growth that attracts aphids.
Excess leafy growth at the expense of hearts/heads in cabbage and the like.
Salt crust and scorched leaf edges in containers; nitrate-heavy leaves.

Signs you are under-feeding iceberg lettuce

Pale, yellow-green leaves, oldest first, and slow growth.
Small, tough, bitter leaves and premature bolting.
Weak, stunted heads in cabbage, broccoli and cauliflower.

If the symptoms point at watering, light or roots rather than nutrition, the full iceberg lettuce care brief covers soil, humidity and the common problems for this species.

Flushing and leaching the salts

For container-grown iceberg lettuce, water until it drains freely each time and flush pots monthly with plain water to stop nitrogen salts accumulating; in the ground, good compost levels naturally buffer this.

Organic vs synthetic feeds for iceberg lettuce

Organic options

Well-rotted manure or compost dug in, plus nitrogen-rich liquid feeds like diluted chicken-manure pellets or nettle feed. UK: pelleted chicken manure or Westland; US: Espoma Garden-tone or blood meal. Steady and soil-building.

Synthetic / liquid feeds

A balanced feed at planting then a high-nitrogen liquid or granular side-dress — UK: Growmore then a nitrogen feed or Phostrogen; US: a 10-10-10 then a high-N (e.g. 21-0-0) side-dress or Miracle-Gro.

Brand names are examples, not endorsements, and UK and US ranges differ — check the label’s own NPK and dilution rate, since formulations change.

Fertilising iceberg lettuce — frequently asked questions

What fertiliser does iceberg lettuce need?

A nitrogen-leaning feed (higher first number) or compost-rich soil — nitrogen drives the fast, tender leafy growth this crop is grown for. Phosphorus and potassium matter far less here than for fruiting crops. Iceberg Lettuce is grown entirely for its leaves, so nitrogen is the priority — steady, nitrogen-leaning feeding keeps it growing fast, tender and unbolted.

How often should I feed iceberg lettuce?

Feed lightly with a balanced fertiliser early to support steady growth and firm heading; avoid heavy nitrogen, which produces soft heads that are slow to firm and prone to rot. Feed lightly with a balanced fertiliser early to support steady growth and firm heading; avoid heavy nitrogen, which produces soft heads that are slow to firm and prone to rot. In practice: a balanced or compost-rich start, then a nitrogen side-dress or liquid feed every 3-4 weeks through the cropping period in the main season (spring through early autumn).

What strength of feed for iceberg lettuce?