Our grapefruit tree is about 6 years old and although fruiting, the fruit is very dry. I have used citrus fertiliser on the drip line and water it in summer. How can I grow juicy grapefruit?
After looking at the picture you supplied, it would be a good idea to remove the plants growing underneath the tree. The reason is that with all citrus, the roots that take up nutrients and moisture are very close to the surface of the soil. If the tree is competing with other plants for soil moisture and nutrients, the result can be young fruit falling off at an early stage and older fruit becoming dry before ripening.
To avoid this, remove the plants and apply a layer of mulch from the trunk to the edge of the drip line to a depth of 6-8cm. This will help retain moisture in the soil and allow the tree to take up nutrients. Citrus are ‘gross feeders’ so apply Daltons incredible edibles® Citrus Fertiliser just outside the branches’ drip line at six-weekly intervals from late February through to early April, recommencing in late October to early December.