Plant is watered and fertilized regularly; this is second harvest.
Ultimately, this happens from unavailability of phosphorus.
This can be due to a low soil pH, too much nitrogen, or a true lack of phosphorus in the soil.
This article will offer more information: https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-fruit-thick-rind.htm
Here are some articles to help you test your soil: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
This article will help you to amend your soil: https://www.gardeningknowhow.com/special/organic/the-importance-of-soil-for-an-organic-garden.htm
Is it best to strip fruit from a grapefruit tree when new blossoms arrive?
Here are two articles that should help:
https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-blooming-season.htm
https://www.gardeningknowhow.com/edible/fruits/grapefruit/harvesting-grapefruits.htm
It wasn’t getting enough sun, so we moved it to a sunnier ares, near a calamondin tree. It was about 3 years old.
If your soil test confirms that you need to feed then it will be fine. If your soil test confirms that there is plenty of nutrients already in the soil, then feeding will harm the tree.
Here is an article to help with the care of grapefruit:
https://www.gardeningknowhow.com/edible/fruits/grapefruit/growing-grapefruit.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
We just moved into a house with several fruit trees. One is some type of grapefruit tree and we noticed ontogeny back of the tree the bark is peeling off and there are strange light colored spots on the bark. We also have what we think is a tangerine tree that also has the spots and looks like it might be getting ready to have the bark peel?
They appear very aged! Most Citrus have a lifespan of around 40 years, give or take 10 years or so.
After this, they start to decline very quickly. This appears to be what is happening. At this point, all that you can do is care for the trees, as usual. Once they begin to fall apart, you can help them by cutting them down.
Here are some articles that will help you to care for citrus:
Live in southern calif. Have a grapefruit tree over 100 yrs old produces fruit year round. But I have so many leaves that they block the sun to the lower limbs of tree. Should I cut the leaves away if so when is best time since fruit is constant on tree?
Research says not to prune grapefruit trees because disease could set in. Since your tree is so old, I would contact your local Cooperative Extension Service or an arborist before doing any trimming.
For other citrus trees, it is recommended to remove diseased, damaged or dead branches and to thin the canopy if needed to let light in. However, I would consult a tree expert before even doing that on a tree so old.
Here is general pruning information:
https://ucanr.edu/sites/Tuolumne_County_Master_Gardeners/files/160549.pdf
Temperature fluctuations, improper watering, or scale insects can all cause yellow leaves dropping. If your tree is established, a deep watering once a week is all it needs except in times of dry periods.
Check your cultural conditions, check the leaves for bugs, and a soil test would help if it's a nutritional problem.
https://www.gardeningknowhow.com/edible/fruits/grapefruit/growing-grapefruit.htm
fruit small green grapefruit. The tree looks sick. I do not have a camera/
Unfortunately, without a photo it can be impossible to diagnose illness. My best guess from the description will be bacterial or fungal infections. This is most common when the tree receives too much water, or the soil does not have a chance to dry out thoroughly between watering.
I would recommend using fungicides according to all labels and instructions, as well as making sure that the tree receives little, to no extra water unless the soil becomes bone dry down to a depth of about 5 inches or more.
Here are some articles that will help:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
https://www.gardeningknowhow.com/special/organic/biofungicide-information.htm
https://www.gardeningknowhow.com/edible/fruits/grapefruit/growing-grapefruit.htm