I have a Tuscan lemon tree which is currently in the conservatory. I spray the leaves every 3/4 days and overall it looks healthy. However, some of the leaves have small white patches on them. Can anyone tell me what this is?

~hi there
it depends on whether the small white patches are mealy bugs which are a problem as are scale insects or whether they are small burns from sunlight on drops of water!

see rhs guidance

The citrus family includes such familiar fruit as oranges, lemons and limes; while small plants are not difficult to grow in pots, given the right conditions, overwintering them successfully is difficult without a conservatory or glasshouse.

Citrus are not demanding plants, but a conservatory or frost-free glasshouse is a must for anyone wanting to grow them well. They do not make happy house plants in winter, when light levels and humidity are usually too low, and centrally-heated rooms indoors are usually too hot.

Equally, citrus are not well suited to year-round outdoor culture, as the combination of winter wet and cold readily kills young citrus plants in the UK. Examples of outdoor success are largely limited to a handful of more-mature plants in sheltered London or south-coast gardens. For healthy plants, provide a winter minimum of 13°C (55°F) for calamondin orange, 10°C (50°F) for lemons and 5–6°C (41-43°F) for many other citrus.
Citrus x meyeri 'Meyer'. Image: Tim SandallSelecting the best

Citrus is a wonderfully diverse genus, from breakfastbowl-sized grapefruits to diminutive kumquats, and from pretty limes to bizarrely-shaped Citrus medica var. digitata (Buddha’s hand).

Popular choices include:

Citrus sinensis (sweet orange): a slow-growing citrus. Try juicy ‘Valencia’ or virtually seedless ‘Washington’.
Citrus aurantium (bitter orange): not as popular as sweet oranges but does have attractive foliage. ‘Bouquet de Fleurs’ has particularly highly-scented flowers.
x Citrofortunella microcarpa (calamondin orange): dwarf, hybrid plant with fruit suitable for preserves and marmalades.
Citrus reticulata (mandarin orange): one of the few spineless citrus. Matures quickly but needs warm conditions (18°C/65°F) in spring to induce flowering.
Citrus limon (lemon): C. x meyeri ‘Meyer’ is still one of the most popular and hardy lemon hybrids, with prolific cropping; C. limon ‘Garey’s Eureka’ is similarly reliable. For a lemon-lime hybrid, grow C. ‘La Valette’, while ‘Variegata’ has highly ornamental green and cream foliage and stripy young fruits.
Citrus aurantiifolia (lime) and C. hystrix (kaffir lime): key lime is compact with small fruit; kaffir lime leaves are used in Thai food.
Citrus medica (citron): an old ‘heirloom’ citrus from which candied peel was made.
Citrus x paradisi (grapefruit or pomelo): quite tender, especially when young, and may take a few years to begin cropping.
Fortunella japonica and F. margarita (kumquat): close relatives to citrus and fairly hardy, kumquats produce thin-skinned fruit eaten whole, either raw or candied.
When first brought indoors, citrus often respond by shedding a large proportion of their leaves. Image: Tim Sandall
The yellowing of leaves is encouraged by over wet or too dry roots. Image: Tim Sandall
Growing citrus

During summer, stand citrus plants outdoors in a sunny, sheltered spot such as a south-facing patio. Water regularly and feed weekly with a summer citrus fertiliser. As the weather cools in autumn, bring the pots into a conservatory or glasshouse, reduce watering and stop feeding. A few leaves may yellow and drop from the initial change of environment. Excessive leaf drop suggests overwatering and either too high or too low a temperature. If in doubt, let the compost dry slightly between waterings. Repot only in spring, using a John Innes No 2 potting compost with extra grit or sharp sand. If the roots are not congested, simply topdress by replacing the top 5cm (2in) of compost.
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 fruits on younger plants.
Pruning

Remove congested growth in early spring, and pinch out shoot growing tips in summer. If renovation is required prune back by two-thirds in early spring.
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
Citrus leaf yellowing - Lack of light, lack of feeding, erratic watering, or low temperatures can all cause this problem.
Flowers fall before fruit sets

Dryness at the roots and lack of air humidity can cause failure to set fruit. Flowers do not need artificial pollinating.
Fruit fall

Fruits should ripen in a period of warm sunny weather, taking almost a year to develop to full size. Most cultivars set too much fruit for the size of the plant. Some of these will be shed but clusters should be thinned to one fruit each on young plants.
Leaf drop

Caused by draughts, too low or high temperatures in winter, often coupled with too much water in winter. Citrus prefer a cool winter rest. Provide lemons with a minimum winter night temperature of not less than 10C (50F) and calamondin oranges 13C (55F).
Leaf yellowing

There are several possibilities - too wet or too dry at the roots, draughts, too low temperatures, lack of feeding or red spider mite infestation.
Rotting roots
Can be caused by overwatering. Cut away damaged roots with some of the compost and repot in a smaller container. Keep the plant in a cool position, watering with care, in the hope that the plant may be able to make new root growth and recover.

If in doubt as to the reason for a decline in growth and appearance, remove the plant from its pot and check the root condition. If roots are firm and healthy, then evaluate the plant's situation and surroundings. If the roots are crowded repot in spring.
Pests of citrus

Citrus can be attacked by aphids, mealybugs and spider mites, but the most common and persistent pest is soft scale, which sucks sap from the leaves and stems.
Symptoms

Soft scale (Coccus hesperidum) is a flat, oval, yellowish-brown insect, up to 3-4mm long, feeding mainly along the larger leaf veins on the underside of leaves. Citrus foliage becomes sticky, as honeydew excreted by scale insects accumulates on the upper leaf surface, and often develops sooty mould. Soft scale also attacks many other plants, including Ficus and bay.
Control

Honeydew and sooty mould can be wiped off the foliage with a soft, damp cloth. This will also remove some of the scales. Persistent infestations may need pesticide treatment. For plants with edible fruit, use a plant oil spray (such as Vitax Organic 2 in 1 Pest and Disease Control or Scotts Bug Clear for Fruit & Veg) or fatty acids (Bayer Organic Pest Control, Greenfingers Organic Pest Spray or Doff Greenfly and Blackfly Killer). Several applications at 10-day intervals are needed to control the more vulnerable, newly-hatched scale nymphs.

Non-edible, ornamental citrus plants can be sprayed with the systemic insecticides imidacloprid (Provado Ultimate Bug Killer), acetamiprid (Scotts Bug Clear Ultra Gun), thiamethoxam (Westland Bug Attack ready to use) or thiacloprid (Provado Ultimate Bug Killer Ready To Use). These controls can also be used against aphids, mealybugs and spider mites on citrus plants where the fruits are not going to be eaten.
Citrus care
Watering

In winter, water moderately with tepid water, allowing the surface to partially dry out before watering, then water thoroughly, allowing excess moisture to drain away. In summer, water freely but do not allow the base of the pot to stand in water.
Feeding

Citrus respond to generous feeding. Use a high nitrogen liquid feed from early spring to mid-summer. Change to a balanced feed from mid-summer to late autumn/early winter. Special citrus feeds are available.
Humidity

Provide a buoyant atmosphere by standing plants on a large saucer or tray filled with damp Hortag or gravel. Mist the leaves in early morning in summer.