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Welcome to our Head Gardener’s Journal

In this monthly column, we will share technical aspects of our work and also keep you up to date about ongoing projects. If there is any topic you might want to hear more about, please ask during your next visit!

Growing Grapefruits

During the 17th century, the cultivation of pineapples fascinated European gardeners. Vast heated pineapple stoves were specially constructed to grow these exotic fruits, and it was considered the ultimate symbol of luxury, fit for a king with the first fruit grown in England presented to King Charles II in 1677 by his royal gardener John Rose, kneeling before him with the fruit.

However, the challenge of growing exotic fruit at Morton Hall in 2021 is slightly different as it is not pineapples, we are growing but grapefruits.

Botanically speaking, grapefruits are an interspecific hybrid between a Jamaican sweet orange (Citrus x sinensis) and an Indonesian pomelo (Citrus maxima). Citrus species hybridise frequently, and this natural hybrid originated in Barbados after both species were introduced from Asia in the 17th century. It was given the scientific name Citrus paradisi in 1830 but it wasn’t until the 1940’s that its true hybrid origins were determined, and the name was updated to Citrus x paradisii to acknowledge the cross between the two species. Today, around 9.3 million tonnes of grapefruits are harvested annually with 53% of the fruits grown in China.

The grapefruit tree at Morton Hall was grown from a seed sown from a supermarket grapefruit over 15 years ago. The consensus at the time was that this would not work. Now, to our utter surprise, a large mature plant it has begun to flower and produce fruit!

Grapefruits are evergreen subtropical trees and require a minimum temperature of 15°C throughout the year. In the UK, this means that grapefruits can only be grown in a heated greenhouse. Over the past
year, we have installed a Hotbox fan heater into our larger greenhouse to maintain a minimum temperature during the colder winter months. Grown in a large pot, we have also been regularly feeding with specialist citrus liquid feeds in both the winter and the summer. During the summer months we have been feeding on a weekly basis with a high nitrogen feed to encourage vigour and avoid premature ripening, fruit drop and leaf discolouration. We then applied a more balanced winter feed monthly from October until March to prevent leaf fall and maintain the health and vigour of the plant during the colder winter months. Aphids have been the main pest affecting the grapefruit tree over the past year but a regular spray with SB Plant Invigorator in the spring and jetting off with water has stopped them from establishing and becoming a problem.

Left, Grapefruit tree in the heated greenhouse at Morton Hall. Right, the grapefruits ripening

The grapefruit tree has produced 6 fruits over the past year, and we have supported the heavy developing fruits with soft nets to prevent the tearing and breaking of branches supporting the fruit and the fruit being broken off prematurely. There are three particularly large fruits that are ripening well on the tree, and we are hopeful with the help of the heated greenhouse and consistent feeding that they will ripen fully before the end of the year.