Citrus are not hardy in the UK but if planted in containers can be grown outside for about 6 months of the year - before being moved into a conservatory or sunny glasshouse.

Water and nutrition

Water freely in summer, but don't allow the pot to stand in water. Water moderately in winter, allowing the surface to dry out partially between waterings. Mist leaves in early morning in summer, or stand on trays of moist Hortag to increase humidity. Feed with a specialist citrus fertiliser from March to October according to the manufacturer’s instructions. Don't feed during winter, or for five to six weeks after repotting.

Temperature

Although Citrus prefer a cool winter period, when little growth occurs, they are not fully hardy in the UK and should be overwintered indoors or, if in a very sheltered place, can be wrapped in horticultural fleece. Minimum winter night temperatures vary with species but on average is about 10°C (50°F). Citrus can be placed in a sheltered site outdoors from June to September.

Pollination

Fragrant white flowers are borne on one-year-old wood from December to February. Warmth and humidity encourage good flowering. Flowers are bisexual and self-pollinating, so don't require artificial pollination. Fruits take almost a year to develop fully. Thin out fruits on younger plants.

Pruning

Remove any congested growth in early spring, and pinch out the growing tips of any long shoots in summer. If renovation is required, prune back by two-thirds in early spring.

Compost

Grow Citrus in a nutrient-rich compost such as John Innes No 2, adding 20% by volume horticultural grit. Repot in spring when plants become pot-bound. In years when not repotting, topdress in spring, removing the top 5cm (2in) of compost and replacing it with fresh compost.

Problems

• Flower fall before fruit set: dry roots or lack of humidity
• Flower failure: poor light, poor nutrition, erratic watering or cold
• Leaf yellowing: excessively wet or dry roots, draughts, cold or poor nutrition
• Leaf fall: cold, draughts, high winter temperatures or over-watering