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Hardy Yuzu tree (Citrus junos) - Growing guide
These trees are grafted on to yuzu rootstock. This unique grafting of yuzu on yuzu exploits the yuzu trees ability to survive low temperatures and adapt to a variety of soils. It also assures excellent affinity between root and graft and reliable fruiting of genuine yuzu fruit, as this is dictated by the carefully selected graft.
The trees are suitable for growing in pots indoors or out, they can also be planted into the garden two years after purchase. They are expected to flower the spring after purchase and within two years will hold fruit to harvest if conditions allow. Rapid and extreme changes in temperatures can cause flowers and fruit to fall early. Fruits ripen throughout the year ready for harvest during October – December. All trees stand 100-120cm tall (including pot) and were grafted a minimum of 18 months ago.
To establish the tree, grow in a pot for the first two years and move to protected spot over winter to protect it from frost. Trees can then be planted out during the spring growing season. They should still be protected from frost for a further 3 years. After that, they will tolerate temperatures down to -10ºC, even lower for brief periods. They will tolerate alkaline soils but thrive in acidic conditions.
The yuzu tree is a hybridisation of a sour mandarin and the lemon-like Ichang papaeda. It is from the Ichang papaeda that the yuzu inherited its ability to stand cold temperatures. Yuzu is the best known of the Japanese citrus fruits, the juice combines grapefruit and mandarin flavours with unrivalled zest. The skin of the fresh fruit carries a powerful hit of citrus with a striking, floral aroma. An essential element of Japanese cuisine, yuzu is used to flavour ponzus, soy sauces, miso and European chefs have embraced its famously tart juice and zest using it in dishes with fish, white meat, sorbets, ice creams and cocktails.
Outdoors a sunny, south-facing, sheltered spot is desirable. Acidic soils are preferable, clay soils should be mixed with sand to allow for good drainage and mounding the earth above the soil level is recommended in these conditions. In dry conditions once or twice weekly watering is preferable to little and often. Waterlogging is the most common ailment in the UK climate so please follow the drainage advice above and prevent the tree sitting in water.
In containers use free-draining compost, additional perlite or hardwood bark will improve drainage if the compost does not already contain these. Irrigation should be controlled so the plant is well watered and allowed to dry out, rather than kept permanently moist. Re-pot every 1-2 years increasing the size of the pot each time by 20-30%. Raise the base of the pot above the surrounding ground to allow for free drainage of any excess water. If you choose to keep your pot outside some of the year and move in for winter, remember to use a light pot so you can lift it.
Caring for your plant
A controlled release, nitrogen-rich citrus fertiliser applied in spring will support growth, liquid fertilisers should be applied in low strengths little and often to prevent excessive levels. Follow the product instructions.
The most likely pest attack would come from aphid or mites. Encourage natural predators like ladybirds, lacewings and spiders. If evidence is seen a spray bottle filled with water and a couple of drops of mild dish detergent will usually deter them. Keep trees dust-free (mites loves dust) by gently rinsing the leaves with a very mild soap or rinsing outdoor trees with a hose every couple of weeks.
All citrus trees require a period of nighttime temperatures below 12ºC for optimum spring flowering. If flowering is prolific in the first two years, it is recommended to remove some of the fruits when very small, so the tree is not overburdened. A first- and second-year harvest of up to 12 fruits is considered sustainable.
Be warned, yuzu trees wear their hardiness on the outside sporting sharp thorns that will make themselves known if not handled with care. These can be removed if they are a hazard.
Trees may sprout shoots below the graft, these should be removed as soon they are observed.
Highly fragrant, small white flowers appear with the spring and fruit is ready to harvest in October – December for a seasonally citrus lift to Christmas and the New Year.
Pick from the tree when the skin is a bright yellow. Dark spots or stains on the skin are normal and a sign of ripeness. Any early fallers can be used green for an extra tart yuzu juice. The zest of both ripe and unripe yuzu is added to soups, dressing, drinks and is used as a topping to sushi and fish. If you have a bumper harvest yuzu freezes whole with excellent results for both the juice and the zest.