Grapefruit are an interesting thing. They are a hybrid, thought to have been created accidentally, of sweet orange and pomelo – a backcross, since sweet orange is itself a more ancient hybrid of pomello and mandarin. Grapefruit come in many different varieties, some sweet and tart, others extremely sour and acid. They come in many different varieties. Like other citrus fruit trees, grapefruit trees are not grown outside year round in the UK. Amongst citrus fruits, grapefruit is one of those which requires more warmth and so unless you are able to keep your polytunnel at a high temperature throughout the year, it is likely that you will keep your grapefruit inside your home in a heated conservatory or porch area over the winter months. That said, a polytunnel could be the perfect place for your grapefruit tree during the summer months.
Grapefruit are treated in much the same way as other citrus fruits. While it is possible to grow grapefruit trees from seed, for a productive tree you will need to get a grafted sapling from a garden centre or plant nursery. Bear in mind that you will have to give grapefruit trees a minimum temperature above 15 degrees Celsius throughout the year. The other thing to bear in mind is that grapefruit trees can be rather sizeable and tend not to fruit for a long time. Young trees will only fruit in ideal circumstances and only after around four or five years. On the plus side, you only need one tree for viable fruit, as grapefruit are self-fertile.
These trees do require a good watering regime and regular feeding – they are hungry plants. When tending to your grapefruit tree, remember that these can be thorny, so protect your hands and arms. Many citrus trees grow thorns at some point – these can simply be pruned away if they are a problem to the crop or the gardener.
Grapefruit trees should only require the most minimal pruning, if any is required at all. Do bear in mind, however, that grapefruit trees will require far more space than other citrus trees that can be grown in pots. They will tend not to fruit unless they grow to a reasonably large tree.
You will know that grapefruit are ready to harvest when the fruits are yellow all over. The fruits can then be taken from the tree when you wish to eat them.