Even his 10-year-old son, Isaac, says he can't get enough. It's a good thing they have a bountiful supply of the fruit growing at their 35-hectare orchard, on the banks of the Hawkesbury River.

About 1500 Imperial and 300 Hickson mandarin trees have peppered Watkins's orchard for 13 years. The plot of land that yields his livelihood was granted to his ancestor, James Watkins, in 1867, but it was Thomas Watkins who settled near Wisemans Ferry in 1836.

The first five generations of his family and others on the Hawkesbury River ''tried to grow everything'', Watkins says, including wheat, lettuce, strawberries and tomatoes. They struck gold with apple and orange crops about the turn of the century.

''My father's great-great-grandfather, Alfred Watkins, grew apples on the flat and for 40 years they were very successful,'' Watkins says. ''He also did really well with his navel oranges because during the war years many Americans came and he got really big money for his produce.''

They also grew Emperor mandarins. Mark's father, John, 75, says: ''They [grew] so high he needed to stand on a ladder, which was placed on a dray that a horse pulled.''

He has an enduring memory of cattle from an adjacent farm getting in and gobbling up the mandarins. ''I was seven and my grandfather was very annoyed.''

When the wet years of the 1950s struck, the orchards were wrecked. The family stopped growing them but in 1987, John remembered the mandarin trees that once towered over him as a child and decided to plant a new orchard. He acquired a new farm and planted the popular Imperial variety.

The rows of trees that stand in Watkins's orchard look similar in height and breadth but the weight of the fruit each produces varies. The Imperial mandarin trees usually yield about 80 kilograms of fruit each winter and the Hicksons about 20 kilograms more.

''It's a temperamental crop,'' Watkins says. ''Last year some of the bigger ones were dry and the sweeter ones were small. This year it's the other way around.''

Mites are the cause of his biggest headaches. ''When those little things get into the flower and eat the back of it, the fruit will fall off,'' he says. ''If they eat the fruit, when it grows it has all these unsightly marks on it.''

In spring, at petal fall, he sprays his trees with copper spray mixed with wettable sulphur. In summer he monitors for olive or rod scales and usually opts to control the pests with eco-oil or lops the branch.

Watkins spreads four large bags of mushroom fertiliser around the base of each tree and uses chicken manure and a blend of fertiliser. He believes good pruning is the key to a healthy crop. He says opening the tree in the middle rids it of diseases and other problems. He also grows cumquats and guavas.

He prefers to munch on Hicksons, which hold higher juice content and spoil him with an intense, sweet flavour. But his son's favourites are the smaller Imperials, possibly the most popular type in the country, which are puffier and therefore easier to peel.

Isaac and his older sisters, Rachel and Laura, form the eighth generation of the Watkins family of the Hawkesbury. Since the farm opened to the public for fruit picking two years ago, business has improved and Isaac's aptitude for engaging with customers has come to light.

''It's a cool job. I'm good with the customers, plus I love eating the mandarins,'' he says, sounding just like his dad.

Watkins Orchard, 1125 Singleton Road, Wisemans Ferry, is open for fruit picking on weekends (10am-4pm) until October.

Weekday visits require booking (phone 4566 3107, see watkinsorchard.com.au). Mark Watkins sells his mandarins at Eveleigh Farmers' Market, 243 Wilson Street, Darlington, Saturdays (8am-1pm).