Field Tomatoes Production Guide

General

Tomatoes are a warm-season, predominantly summer crop, but they can be grown in certain frost-free lowveld areas during winter. Temperatures just a few degrees above freezing will damage both the plant and fruit. The optimum temperature range for growing tomatoes is between 20°C and 28°C. Temperatures below 12°C or above 35°C can lead to flower drop and significant yield losses. Continuous moist or rainy weather favours the rapid development of leaf diseases and makes control difficult. For best results, aim to finish the crop by late December or early January. However, it's worth noting that prices tend to peak during this time and again in mid-winter due to consistent shortages.

Soils

Tomatoes grow best in deep, fertile, humus-rich, and well-draining soils. Suitable soil types range from sandy loam to clay loam, with a clay content between 15% and 35%. Sandy soils can also be used, provided that soil moisture levels are properly maintained. Tomato roots can extend over 2 metres deep, though the highest concentration lies in the top 600 mm. Deep ploughing or subsoiling is essential to break up any old plough pans and allow roots to penetrate deeply. The ideal soil pH is between 5.0 and 5.8. Tomatoes should be grown in rotation—ideally one crop every three to four years—to reduce problems from nematodes and diseases. They perform particularly well when planted after a green manure crop that has been ploughed in and decomposed fully.

Fertilizer

Fertiliser applications should be based on soil analysis. However, as a general guideline, apply High C at a rate of 750–1,000 kg per hectare.

Top Dressings:

• Week 1 after transplanting: 25 kg/ha Mono Ammonium Phosphate (MAP)
• Week 2 after transplanting: 50 kg/ha Ammonium Nitrate (AN)
• Week 3 after transplanting: 50 kg/ha Ammonium Nitrate (AN)
• Week 4 onwards: 50 kg/ha Ammonium Nitrate (AN) + 50 kg/ha Sulphate of Potash (SOP)

Stop all fertilisation two weeks before the final harvest.

Micronutrients are also essential for high yields. Important elements include: Calcium (Ca), Magnesium (Mg), Sulphur (S), Boron (B), Iron (Fe), Copper (Cu), Zinc (Zn), Manganese (Mn), Molybdenum (Mo). These can be supplied through micronutrient mixes such as Vege Oemff.

Calcium is especially crucial. A deficiency can lead to Blossom End Rot. Weekly foliar sprays of Calcium Nitrate should begin at first flowering. Apply at a rate of 10 g per 1 L of water, using 250–300 L of water per hectare.

Planting & Spacing

Tomatoes are best established using propagated seedlings. Choose healthy, strong, well-rooted seedlings for optimal results. Transplant into moist soil and firm the soil around each plug to ensure good soil-to-root contact and promote early root development. Irrigate immediately after transplanting to help seedlings settle in. Row spacing typically ranges from 1.2 m to 1.8 m, with in-row spacing of 40–50 cm. This results in a plant population of approximately 16,000–22,000 plants per hectare.

Irrigation

Drip irrigation is recommended for best results, as it allows precise watering based on tensiometer readings that measure soil moisture. It also keeps foliage dry, reducing the risk of leaf diseases. Overhead sprinkler irrigation can be used in drier months, up to the fruiting stage, where there is no rainfall. However, in areas with moderate rainfall or mist, sprinklers can significantly increase disease pressure. In general, the crop will require 400–600 mm of irrigation, depending on soil type, temperature, and humidity. The use of tensiometers and an evaporation pan is strongly recommended to guide irrigation scheduling.

Trellising

Trellising is strongly recommended for table tomatoes. It reduces the incidence of disease, pest damage, and sunburn, while improving overall fruit quality, marketable yield, and ease of harvesting. Use poles 50-70 mm in diameter, buried to a depth of approximately 600 mm and spaced every 3 metres, with 1.4–1.8 m remaining above ground. End poles should be thicker and well-anchored to handle the weight of the crop. Install trellis wires early to avoid damaging young plants.

Pests

Diseases

Weeds