Ice Berg Lettuce Production Guide

General

Lettuce can be grown in summer, but specific precautions must be taken to ensure the crop's viability. The most favourable daily mean temperature is between 15°C and 18°C. However, lettuce will perform in a range of 17°C to 27°C during the day and 2°C to 12°C at night, provided suitable varieties are selected.

Soils

Lettuce is tolerant of a range of soil types but performs best in light sand to sandy loams. Due to its shallow root system, lettuce can be grown in relatively shallow soils, provided a good irrigation system is in place to maintain favourable soil moisture levels. Most lettuce roots extend only to a depth of around 300 mm, so nutrient and water applications must be concentrated within this limited zone.

If planting in soils that cause staining—such as red soils—applying a mulch between the soil and the bottom leaves will help prevent soil stains, which can spoil the heads and reduce marketability. Washing off soil stains is not recommended, as it can lead to bacterial rot. The ideal soil pH is between 5.5 and 6.0.

Cultural Practices

To achieve the best results, soils should be well-prepared in advance, especially for summer production. Raised beds, 20–30 cm high, are recommended to improve drainage during periods of excess rainfall. In winter, planting on flat ground is acceptable. Drip irrigation is the preferred method, as it avoids soil splash and contamination of the heads. If using overhead irrigation, fit smaller nozzles to the sprinkler heads to minimise droplet size and reduce the risk of soil splashing onto the leaves.

As moisture is critical in lettuce production, the available water in the root zone should not fall below 50% of holding capacity before the next irrigation. Water requirements vary from 18 mm per cycle on sandy soils to 50 mm per cycle on heavier soils. Lettuce benefits from light and frequent irrigation, even more so than many other crops. However, frequent watering, especially in summer, can promote the development of several diseases.

Planting & Spacing

Using high-quality speedlings is highly recommended to ensure a uniform and healthy crop. In the nursery, lettuce seedlings typically take about 5 weeks to mature in winter and just under 4 weeks in warmer months. Before summer transplanting, seedlings should be well hardened, as they will face high field temperatures.

Mulching is highly recommended for summer production. Apply mulch such as wheat straw, grass, or sawdust after transplanting. This helps reduce soil temperature, conserve moisture, cool the crop, and prevent soil splash. In summer, raised beds are recommended due to uncontrolled heavy rains. Beds should be spaced 1.5–1.8 m from centre to centre. On each bed, mark out 3 rows 30 cm apart, with seedlings planted 25 cm apart in the row, giving a population of around 80,000 plants per hectare. For larger head sizes, increase in-row spacing to 30 cm, reducing plant population but allowing better head development.

On flat ground, rows should be 35–45 cm apart, with in-row spacing between 25–35 cm, resulting in a population of approximately 60,000 to 100,000 plants per hectare. For orders requiring larger head sizes, use wider spacing.

Fertilization

A soil analysis should be done before planting to determine specific nutrient requirements. As a general guideline, apply a basal dressing of High C at a rate of 500–600 kg per hectare prior to planting. If fertiliser is applied by hand into each planting hole, ensure it is well mixed with the soil to prevent seedling root burn.

Top Dressing

Top dressing should be done approximately 8–10 weeks after transplanting.

Pests

Diseases

Weeds