Citrus are frost tender plants and temperatures below 7°C (45°F) may cause damage or even death. For this reason, in most parts of the UK, it is best to grow citrus in containers that can be moved to a warmer position over winter.
They are quite hungry plants, so use nutrient-rich 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.
Sharp sand is washed, gritty sand used in potting compost mixes, This is sold for gardening and is not the same as builders sharp sand.
A series of soil-based seed and potting composts made to specific formula developed by the John Innes Horticultural Institute in the 1930s. Most mixes contain loam, sand, peat substitute, ground chalk and varying amounts of added fertilisers, according to their purpose.
Plants can be placed outdoors in summer, from mid-June to late September, if sheltered from cold winds. At other times, keep them in a cool greenhouse or conservatory. Citrus are not ideal houseplants, as the heat and dry atmosphere can cause scorch.
Citrus like cool, but not cold, conditions in winter, as a little growth does take place. A minimum winter night temperature of 10°C (50°F) is fine for lemons. Calamondin oranges need at least a minimum winter night temperature of 13°C (55°F). Other species will tolerate cooler conditions, not falling below 7°C (45°F).
Watering
Citrus originate from regions of free-draining soil but high air humidity, and it is important to keep the air The concentration of water vapour in the atmosphere. This affects the rate at which plants transpire (lose water from their leaf pores), which in turn affects how much water their roots absorb from the soil. If air humidity is low, plants transpire quickly and become at risk of wilting if water is lost from the leaves faster than it can be absorbed by the roots. Different plants require different levels of humidity to thrive. Many tropical houseplants need high humidity and are best grown in a steamy bathroom, misted regularly or placed on a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor or overhead misting.
In summer, water freely but do not allow the base of the container to stand in water.
In winter, allow the surface to partially dry out before watering, then water thoroughly with rainwater, allowing excess moisture to drain away. Overwatering in winter is one of the commonest causes of stress in citrus, so keep them on the dry side.
Feeding
Citrus require feeding throughout the year. From late March to late October, use a summer feed high in nitrogen. Use a more balanced winter feed from late October to late March. These are available from nurseries and garden centres, including fertilisers specifically formulated for citrus.