Romaine Lettuce — DutchGreenhouses

Romaine is the upright, elongated head with a firm midrib, sold wholehead and as hearts. It is commercially important across Europe and the Middle East and is a frequent request in project briefs.

What the crop needs

The crop is short-cycle and hydroponic. The upright head encloses its inner leaves tightly as it fills, which is the structure most associated with tipburn risk, and the heavy midrib means head weight accumulates in a way that stresses the plant’s water transport late in the cycle.

What the greenhouse has to do

Romaine is the most tipburn-sensitive type in the family, and that single fact drives the specification. Tipburn is a transpiration problem at the leaf margin, so the answer is in the building: air movement through an upright, closing head, humidity control that keeps the plant transpiring, and screening that prevents the swings which stall it.

The upright head shape is the reason. Leaves wrap early and the fastest-growing margins sit deep inside the head where air moves least, so a house that is adequate for an open type can be marginal for romaine. Airflow design, canopy-level ventilation and even transmission across the floor are specified for the closed head rather than for lettuce in general.

DutchGreenhouses® designs the structure, climate, screening and irrigation around the lettuce type, its system and the local climate, so cycles turn at the head quality the market grades on. Get in touch to plan a lettuce greenhouse.

Butterhead lettuce

Soft, loosely wrapped leaves, and the type least tolerant of handling.

Greenleaf / Batavia lettuce

A firmer, more robust head than butterhead, and it travels better.

Hydroponics

Substrate growing with drip supply and drain recirculation.

Climate

Heating, cooling, humidity control and carbon dioxide dosing.

Built to be handled, still cut fresh

Romaine carries more fibre than the soft types and the same raw vitamins, because a salad leaf reaches the plate as it was cut. The heavy midrib is part of that. It is the crunch the type is bought for, and the part a Caesar salad is built around.

Structure buys tolerance, not time. Romaine survives cutting, chopping and dressing better than a soft head does, which is why so much of it ends up in hearts and in prepared salad. It still runs down from the day it is harvested: the rib loses its rigidity, the cut edge browns, and a dressed leaf shows both faster than a whole one.

So the type travels further than its siblings without arriving any fresher. Growing near the market keeps the gap between cutting and eating short enough that the rib is still firm when the dressing goes on, and it holds that through the months a field in the same market cannot supply.

Nutrition facts

Lettuce, cos or romaine, raw

Per 100 g

Energy: 17 kcal
Fat: 0.3 g
Carbohydrate: 3.29 g
Sugars: 1.19 g
Fiber: 2.1 g
Protein: 1.23 g
Sodium: 8 mg
Potassium: 247 mg
Vitamin C: 4 mg

Source: USDA FoodData Central, FDC 169247

Questions

Romaine lettuce, asked and answered

Is head weight or head count the right target?

Lettuce is sold by the head, so the count reaching grade in a year decides revenue. A heavier head grown more slowly can earn less than a lighter head on a shorter cycle.

Does the cultivar matter more than the type?

For head mass, density tolerance and tipburn risk, yes. Those are cultivar properties, which is why a lettuce project is planned around a named cultivar rather than around the type alone.

What causes tipburn?

Calcium not reaching the fastest-growing leaf margins, driven by transpiration and root pressure rather than by supply. Climate control addresses it; adding calcium to the solution generally does not.

From the knowledge base