Tomatoes are particularly prone to what are known as physiological disorders: abnormal growth caused by non-infectious factors. This is partly due to the difficulty of controlling the sensitive requirements of tomatoes for temperature, To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key plant nutrients usually derived from soil are nitrogen, phosphorus and potassium, while carbon, oxygen and hydrogen are absorbed from the air. Other vital soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough nutrients to promote healthy plant growth.
Tomatoes need warmth and will not thrive at temperatures of below 12°C (54°F). Although it is easy in summer to keep temperatures raised in glasshouses, outdoor tomatoes may still require A soft, fibrous, translucent material laid over or around plants hastening their growth and protecting them against weather and pests. Heavier grades of fleece give about 2°C of protection from frost. It is usually used without supporting hoops.
In early summer, the nights can be cold and the days very warm. This fluctuation of temperatures is the main cause of what can sometimes be a very alarming degree of leaf curling. The plant is unable to cope with the accumulation of carbohydrates that occurs if nights are too cold for plant physiological functions to occur normally. Fortunately this does not seem to be a serious cause of loss of crop and usually disappears of its own accord as the nights begin to get warmer in late summer.
Small greenhouses and polythene tunnels used by home growers are much more liable to fluctuating conditions than larger greenhouses.
Mottling and discolouration of older leaves usually indicates a deficiency of nutrients, especially magnesium, and is a less serious problem providing the plant is otherwise vigorous.
Tomatoes are particularly sensitive to Chemical substances that regulate plant growth and development. There are several types of plant hormones, including auxins, cytokinins, gibberellins, abscisic acid and ethylene. These hormones play important roles in processes such as cell division, elongation and differentiation, as well as in responses to environmental stimuli such as light and gravity.
Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.