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.

A series of soil-based seed and potting composts made to specific formulae developed by the John Innes Horticultural Institute in the 1930s. They contain loam, sand, peat (or peat substitute), ground chalk and varying amounts of added fertilisers, according to their purpose.

John Innes compost

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 amount of water vapour in the atmosphere. Different plants require different levels of humidity. Houseplants that need high humidity are best grown in a steamy bathroom, misted regularly or the pot placed in a saucer of damp pebbles. In a greenhouse, humidity can be raised in hot weather by damping down (wetting) the floor, overhead watering or misting. However, high humidity can cause fungal problems, in which case open vents to improve ventilation.

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.

Citrus require only minimal pruning to keep them under control and looking good.

• In February: Reshape plants by the removing overcrowded branches. If plants become leggy, they can be pruned back by up to two-thirds at this time. The leading (tallest) branch may also be cut back to induce bushier growth
• Over summer: Pinch back strong-growing branches by pinching out the soft growing tips between thumb and forefinger

Occasionally, mature plants may produce a number of fast-growing and unwanted shoots known as water shoots. Cut out all water shoots arising from the bottom or middle portions of the main branches, and shorten those arising near the tips of the branches.

Citrus plants are normally sold as mature plants, as they are quite slow-growing. You can try propagating plants yourself by taking semi-ripe cuttings, or grow from seed. Seed-raised plants can take many years to produce fruit and the fruit quality is usually inferior to that of the parent plant, but it can be fun to try and produce some unexpected results.

Growing from seed

March is the ideal month for seed-sowing, but you can try with fresh pips at any time of the year.

1. Sow seeds fresh from ripe fruit at a depth of about 1cm (½in) in John Innes seed or multi-purpose compost at a temperature of 16°C (61°F).
2. Put them in a light place and maintain this temperature until germination.
3. Pot on into progressively larger pots in late winter, as necessary, gradually changing to John Innes No 1 then John Innes No 2, unless multi-purpose composts are used.

There are a number of citrus to choose from of which the following are just a taster;

• Citrus × aurantiifolia – greenish-yellow lime
• C. × meyeri ‘Meyer’ AGM – compact, reliable form of lemon
• C. × microcarpa AGM – small orange
• C. × paradisi – grapefruit
• C. japonica AGM – kumquat
• C. limon ‘Garey's Eureka’ – rough-skinned lemon

Links

RHS Find a Plant
AGM plants

Citrus may suffer problems common to other plants kept under glass, such as red spider mite, scale insects and mealy bug. Also see our page on citrus problems.