– making a success of marginal conditions
Tea is a crop that grows like a weed under ideal conditions and on ideal land, but very few of us are in that fortunate position. Under more marginal conditions it takes some skill and expertise to grow it well. The variation in tea yields across the world demonstrates this: as low as 1/4 ton/acre of Made Tea in China and Indonesia (smallholder farmers), and as high as 1 ton/acre for Indian estates, to (exceptionally) the world record of 4.5 tons/acre for Clone S15/10 in Kenya. Between these wide yield extremes lie some marginal conditions, poor planting material, and some lack of expertise.
What does tea require to do well? In terms of climate, the Teaman’s (or Teawoman’s) ideal would be misty at night, sunny during the day, with rain at tea-time – and not too much cold weather, hail or drought. More specifically for ideal growth tea requires:
- Average air temperature 70 to 95°F – growth becoming dormant if night temperatures are below 50-55°F
- Soil temperature between 60 and 75°F
- Annual rainfall between 1,500 and 3,500 mm (60 and 140 inches), well spread through the growing season
- Soil pH between 4.5 and 5.5
- Soil structure: well drained but retentive. The tea crop can evaporate 3 to 6 mm per day = 1,000 to 2,000 mm per year. Rainfall is therefore marginal below 1,500 mm (60”).
- Water table more than 6 ft below soil surface
- Humidity: high enough not to limit shoot growth (in scientific terms this means a saturation deficit remaining below 2.3 kPA)
- Light intensity: at least 700 to 800 W per m2 – this is typical of winter sun intensity in tropics = 75% of summer levels. Yet of this, only 40 w/m2 will be wasted by reaching the ground under healthy bushes. Tea grown well is an extremely efficient light interceptor but low planting densities, poor pruning techniques and vacancies waste sunlight – and reduce yield.