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 compost such as John Innes No 2, with the addition of 20 percent by volume of sharp sand or grit. Use ericaceous John Innes compost in areas where hard water has to be used for irrigation. There are also specially formulated citrus composts available. Repotting is best done in spring, using only the next size pot.
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).
Citrus originate from regions of free-draining soil but high air humidity, and it is important to keep the air humidity up year round. The best way to do this, is to stand plants on large saucers or trays filled with ‘Hortag’ or gravel and keep the water level just below the surface of the gravel. Mist the leaves in early morning in summer and make sure that there is good circulation of fresh air.
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.
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.
Pruning and training
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.
- 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)
- Put them in a light place and maintain this temperature until germination
- 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