Once a week? It should be 3x. That's the main problem. Three good soakings in the height of long summer days until its a well rooted plant in 3 or 4 years.

My friend live few blocks away water his trees a lot, he also got small fruit. My area full of clay filled many year ago by builder, if I water too much will kill the trees (I had 5 die so far) will the salted air have anything to do with small fruit?

Yeah- they do hate clay as is. I did another post where I said that where I now have a fruiting Mango? I had dug a 3x3 area with a big sack of perlite mixed in for a try of Papaya. They died!..but the Mango planted the next year there, has thrived relative to my climate. I wouldn't claim its fast grower for me like in Florida or even Los Angeles.

If you try again..amend the clay soils somehow to loosen it up. I've even for other tropicals ,bought the largest bag of inexpensive potting soil and blended that in. Its $7 more for the bigger 2cubics +.but worth it for something you dont want to waste years on.

Thank you sir, your weather must be colder than mine, please tell me again about watering and fertilizer for your mango

Its roughly 10f colder in day temps and 6f colder in night temps in winter- Dec and Jan. And mine took last years heavy rains. So,once they get going there is a good chance for long term.

But as low water needy as they might be once they are tree's..young plants need to be kept hydrated in our long California summers. I water 3 x a week by hose. If you have them on drip or irrigation even better and easier.

I like to fertilize when I see it starting to flush in late spring or early summer. No point is fertilizing in the cool months. Best to use a mild ratio. Or very light on the lawn fertilizers since I see them planted in lawns every now and then.