Here's what it takes to have them fruiting in your garden.

Cumquat
Fortunella species
Cumquats (shown above) make a delicious marmalade and the plants are very pretty in pots.

Size
Usually grows to around 2m tall but can be much bigger.

Climate
Humid subtropical, Mediterranean, temperate zones; temperatures below 38C.

Frost tolerance
Takes -5C, possibly lower for short periods.

Flowering season
Late spring to midsummer. Flowers are very small.

Fruiting season
Fruit ripens in autumn but hangs on until mid-spring.

Cross-pollination
Not necessary; self-fertile.

Watering
Particularly from spring to the middle of autumn; less in winter.

Feeding
Late winter and again at midsummer with citrus food as directed on the pack, or rotted poultry manure.

Problems
Scale insects, sap-sucking bugs and aphids.

Lemon
Citrus limon

Lemons ripen on the tree from autumn to spring, though there is generally some fruit at other times.

Size
Reaches 5-6m tall, with a similar spread.

Climate
Humid subtropical, dry subtropical, Mediterranean, and the warmer temperate zones.

Frost tolerance
To -2C. Meyer lemons to -5C at least.

Flowering season
Spring; smaller flushes in summer and autumn.

Fruiting season
Fruit ripens from autumn to spring and after other flushes of flowers.

Cross-pollination
Not necessary; self-fertile.

Watering
Particularly from spring to the middle of autumn; less in winter.

Feeding
Late winter and again at midsummer with citrus food as directed on the pack, or rotted poultry manure.

Problems
Scale insects, bugs, aphids, fruit fly and collar rot.

Mandarin
Citrus reticulata

Valencia oranges also cross-pollinate Ellendale or Imperial mandarins.

Size
Reaches 2-4m tall or more.

Climate
Humid subtropical, Mediterranean and temperate zones.

Frost tolerance
The most hardy varieties tolerate -5C and all take light frosts.

Flowering season
Spring.

Fruiting season
Varies with type from early autumn until spring.

Cross-pollination
Not needed, but fruit set and size are better if Ellendale and Imperial have each other nearby. Valencia oranges also cross-pollinate Ellendale or Imperial mandarins.

Watering
Keep well watered from spring to mid-autumn; less in winter but do not neglect entirely.

Feeding
Late winter and again at midsummer with citrus food as directed on the pack, or rotted poultry manure.

Problems
Sap-sucking bugs, scale insects, aphids and fruit fly. Trees often bear heavily one year with little the next. Minimise this by removing 25-50 per cent of the fruit as it forms.

Orange
Citrus sinensis

Oranges flower in spring. Navel oranges ripen in autumn and early winter; Valencias in spring and summer.

Size
Reaches 2-6m tall or more.

Climate
Humid subtropical, Mediterranean, temperate, and semi-arid zones are ideal. The flavour is usually insipid in the tropics.

Frost tolerance
To -2C, possibly a little lower; trees must be protected from heavy frosts inland.

Flowering season
Spring.

Fruiting season
Depends on variety. Navel oranges ripen in autumn and early winter, Valencia oranges ripen in spring and summer.

Cross-pollination
Not necessary; self-fertile.

Watering
Water most heavily during the warmer months but do not let the soil go dry in winter.

Feeding
Late winter and again at midsummer with citrus food as directed on the pack, or rotted poultry manure.

Problems
Sap-sucking bugs, scale insects, aphids and fruit fly. Navels, which ripen in the cooler months, are less susceptible to fruit fly.

Valencias will often bear heavily one year with little the next. Minimise this by removing 25-50 per cent of fruit as it forms.

Source:Gardening: A Commonsense Guide (Murdoch Books)