Not enough water and going too dry between watering. Is it in a pot?..best to put it on drip so its consistently watered. Mulch too helps.

You might be glad they don't mature. Imagine all those hundreds of fruits maturing at the same time. Eventually they will all fall off at the same time leaving you with 1,000 pounds of fruit to clean up.

Mango growing in California info here. California Rare Fruit Growers local chapters can be a good resource.

Its pretty accurate,the CRFG advice. It doesn't list some newer better California adapted Mangoes. Just by chance,I bought a Baileys Marvel. To make a long story short- that is a fast vertical grower. What we need in coastal California is fast growth..that hardens the tree to winter's cold. Besides it wins taste tests too ( Youtube,the Vegan grower) so I think its a good starter Mango for California. Manila is fine...I like them too. I think the Fremont Mango ( YouTube) is one of those. Its done fantastically well. In five years in went from a 2' stick to a you-can walk-under-it-tree. I once used Google streets for it ( Bruce Street,Fremont) and you could see it growing like a temperate fruit tree over the years.

You did not say where in southern California you are - there are many micro-climates here, and some are better for mangoes than others. I had a Manila mango tree when I lived in Venice, and I got good fruit from it, although never more than about ten in one season. However, they were a good size (like the ones in the grocery store) and were very sweet. Since it very rarely got hot where I lived in Venice and never any danger of frost, it was easy to keep it watered. I had thought that it would require heat, but mine made good fruit without heat.

The Tropical Fruits Forum will also have info on mangoes.

I think Lars is a typical California Mango growing story. I would tell people,if you want plenty of Mango fruit here? Plant many trees. Because any one tree will take a decade or more to have a good number of fruit. The tree's themselves in most areas are never large. Only in the very best climates of no frost in winter and hot in summer will have large California Mango trees. Usually the story on those are its "30-100 years old".

They are nice looking tree's,flush red too. I could see a back yard of 10 trees planted 6' apart along a wall or fence that gets hot..that person will have plenty of fruit every year.

You can't think like Florida or the tropics and expect to see a huge tree in a few short years. Wont happen here.

I am in Riverside Calif. I have lost 90% of the fruits at about 2.5 inches long and they all split/crack along the center. I am sure my soil is not good and too dry. I do water EVERYDAY. MAYBE STILL NOT ENOUGH?

You might try giving the tree a little bit of shade to prevent water stress. It can get pretty hot and dry in Riverside. Mango trees can grow out there but they usually do better as part of a forest canopy with other trees. Keep the tree well watered during the Summer.

Splitting on any fruit tree is usually caused by inconsistent watering. Too dry, then watered..then too dry again,etc.

I doubt you could over water one in summer especially in Riverside. You've got a good sized plant..so you know your 90% there. Just water more and deeper. Mulch it more and continue farther out from the tree so roots can spread.

Mangoes have a very fine sponge like root system.

We water it everyday around 6 PM. We dont have much vegetation around the tree. This problem has been since last 3 years. Last year the fruits were smaller when they split and fell. I do prune the tree every fall. Mostly around it and not much on top.

A larger tree should only improve. Any photos of it?