I saw that the cherry treses were covered with full of cherries.

The sun was a good reason ofcaused them to bearing abundant fruit.

This one was a little difficult to edit...I think you want to include "good" but I'm not sure how to work it in without changing your sentence a lot. Maybe, "Thankfully, the sun caused them to bear abundant fruit" or "the sun was a good impetus/catalyst that caused them to bear abundant fruit" (impetus and catalyst are both a bit academic words but I'm not sure how else to phrase this)

It has been about eight or nine years since he had planted the trees.

I think it's okay without "had"

But the yield was not good until now.

I like this sentence better than the above one.

It looked good when I saw the cherry trees with abundant fruits.

But they were still planted in the pot because he said it was not good to plant it oin the ground.

It's a little more common to just say "they were still in the pot" but if you want to keep the word "planted" it's okay.

He said they need a well-drained soil.

If not, they would be died.

In addition to this good news, I want to say something about my fig tree.

You can say "say something about" or "talk about".

say about (X)
talk about (O)

say something about (O)
talk something about (X)

The branches were broken easilyeasily broken.

Actually it was so small that it wasdidn't overgo past my knees.

When you are talking about height it's common to say "go past".

It washad already grown about a span long.

Some people dig it up and locatekeep it in the house and replant it in spring.

"dig (something) up" = take it out of the ground

It's not wrong to say "locate it in the house" but I think "keep" sounds more natural here.

I didn't know that because I had lots of things to looking after.

I felt sorry about it so I dug it up and replanted it another place where the soil was better.

But now I am more relaxed more than then cause I got some experience.

I will do many other sorts of things as well today.

I saw that the cherry treses were covered with cherries. / I saw that the trees were full of cherries.

You don't need to add "cherry" to "cherry trees" since it is repetitive. :)

The sun was a goodthe reason ofwhy the trees were bearing abundant fruit.

He had lots of blueberry trees, and I bought four trees.

He said they need a well-drained soil.

If not, they would be died.

In addition to this good news, I want to saytalk about my fig tree.

Actually it was so small that it wasdidn't overreach my knees.

I neglected it, and I found the new leaves sprouting out from the bottom yesterday.

It washad already grown about a span long.

I googled it and I found that the fig trees can't withstand the winter.

Some people dig it up and relocate it in the house and replant it in the spring.

I didn't know that because I had lots of things to looking after.

I felt sorry aboutfor it so I dug it up and replanted it in another place where the soil was better.

But now I am more relaxed more thanthan back then because I got sommore experience.

Today, I will do many sort of things as well today.