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The Duncan Grapefruit Tree

Can you imagine a variety of grapefruit that is 200 years old? A grapefruit that has the privilege of being the oldest grapefruit hybrid in the United States? Imagine no longer: the Duncan Grapefruit tree is both of these!

View of grapefruit tree with light yellow fruits on the branches, very similar in appearance to the fruit of the Duncan Grapefruit tree.

This is the Duncan Grapefruit 

A Duncan grapefruit is pale and yellow-fleshed. It has a good balance between the sweetness and tartness of a grapefruit.

The trees produce fruit from fall to spring. Depending on their size, though, the grapefruits can be harvested any time during these months. The trees grow quite vigorously, are quite productive and are relatively cold-resistant.

Closeup of cut grapefruit with pale yellow flesh inside -- the Duncan grapefruit is a light yellow-fleshed fruit, as opposed to pink or red grapefruit varieties.

History of the Duncan Grapefruit Tree

Grapefruits are the result of a natural hybrid between the pomelo and sweet orange. The Duncan Grapefruit tree is the oldest deliberately created a hybrid, dating back to 1830. AL Duncan, who worked in insurance at the time, grafted buds from a grapefruit to a sour orange tree and the Duncan grapefruit was born. Later, hybrids of the Duncan include pink grapefruit and minneolas.

The Duncan Grapefruit tree was popular for years and was once grown prolifically. In the 20th century, however, the public developed a taste for grapefruit with far fewer seeds and even seedless varieties were cultivated. This meant that the Duncan grapefruit became less popular. What was grown was sold to be canned, or for juice.

Recently, though, this heirloom variety has been recognized and is growing in popularity, even though it is in small quantities.

Habitat of the Duncan Grapefruit 

Grapefruit trees usually prefer warmer, more humid areas, which means that the Duncan Grapefruit is usually found in warmer areas. It is also one of the varieties of grapefruit that is more tolerant of cold, so they can be grown in slightly cooler areas too. They do need a lot of sun, though, and a generally warmer area, so this doesn’t mean that the trees can be grown in areas with a very cold winter.

Growing Your Own Duncan Grapefruit Tree

Grapefruit tree bearing round, yellow grapefruits.

When you have planted your Duncan Grapefruit tree, you will need to wait at least three years for it to bear fruit. This is because most of the energy the plant produces will go into growth, so that it can establish itself as a tree before producing fruit.

Position

A grapefruit tree needs sun to grow, so you will need to choose a spot that gets a lot of sun. This means that the tree will be warmer through the year. Try to choose a spot that is slightly sheltered, so that the tree is protected from the cold a bit.

Planting the tree on the side of a wall that faces the sun may be a perfect spot, because it will receive sun for most of the year and also some protection.

Remember that a grapefruit tree can grow to about 4 meters high, with a widespread canopy. This means you should plant it at least 10 feet (3 meters) from any wall, or other obstacles.

Soil

Your Duncan Grapefruit tree grows best in loamy, well-drained soil. If the soil in your yard is clay-based, then you will need to work some sand and minerals into it to improve its quality. Consult your local nursery or garden center, so that you can get specific guidance about your area.

Time

Closeup of light yellow-colored grapefruits hanging on a tree.

Grapefruits are essentially a winter fruit, as the trees bear from fall to spring. To work with this, you should aim to plant your tree in the fall, but this means it will grow through the winter in its first year, so you will need to monitor the water it needs and possibly protect it in the first year.

You can also plant a tree in spring, which will give it time to establish itself before the winter. However, if the summer is warm, then make sure that you water the tree regularly, so that it doesn’t grow out in the early stage of its growth.

Planting

When you plant a Duncan Grapefruit tree, you need to make sure that the hole you dig is big enough to accommodate all the roots and to anchor the tree in the soil. This means that the hole should be at least 6 inches (30cm) wider than the root bowl and at least 2 feet (60cm) deep.

When you have dug the hole, put the tree into the hole and fill it enough so that the tree will stand on its own for a little while. You can press the soil that you fill the hole with down a bit, but don’t tamp it too densely.

Fertilizer

Spread some fertilizer onto the soil around the trunk of the tree, then soak it a bit before filling in the rest of the hole. Make sure that the soil around the tree is at the same level as the rest of the surrounding earth, so that the water does not pool around the tree. This can result in the roots become too wet for too long and root rot can develop.

You should continue fertilizing the tree in early and late summer. Use an ammonium sulfate-based fertilizer.

Pruning

A grapefruit tree should not be pruned aggressively. You should remove the dead or weakened branches. If you do prune the tree too vigorously, then it will affect the growth of fruit in the next year.

Harvesting

The fruit of the Duncan Grapefruit tree can be picked anytime through the winter, although early on may be most suitable. If you leave some fruit on the tree, it will continue to ripen through the winter and may become sweeter.

For a more complete guide on growing a grapefruit tree, visit this link to read our blog article.

Growing a Duncan Grapefruit Tree in a Pot

Grapefruit trees growing in large flowerpots.  It's possible to grow a Duncan Grapefruit tree in a pot if you don't have the space to plant a tree in your garden.

If you live in a cold area, you may still want to try growing your own Duncan Grapefruit tree. This will mean creating an area that is relatively warm all the time and which receives direct sunlight. You may be lucky to have some form of greenhouse, or outdoor sheltered growing area, which may suit you. However, it is most likely that you would need to grow the tree indoors in a pot.

There are two things to remember about growing plants in a pot: the roots become confined, which will affect the growth of the plant; but the pot may become just too small for the roots and they can even break it.’

To grow a Duncan Grapefruit tree in a pot indoors, you will need to get a dwarf variety, which can still grow to about 8 feet (2.5 m). This means the tree will need to be pruned quite regularly, to keep it to a manageable height.

Also, remember to look for any cracks in the pot!

Conclusion

Segments of yellow-flesh grapefruit in a grapefruit rind "bowl" next to whole grapefruits.  Growing a Duncan Grapefruit tree means you can have harvests of fresh, juicy fruit for years to come.

The Duncan Grapefruit is the granddaddy of hybrid grapefruits and is still enjoyed, particularly as it is making a comeback. You just can’t keep a good grapefruit down!

Want to know about other varieties of grapefruit? Visit this link to read other grapefruit blog articles.