Autumn is a nice season, especially when you just come fromsince it's right after summer.

Re: Heavensblade's comment, this is just another way to phrase it

DI associate autumn with a deep sky, beautiful clouds and cool breeze, but one thing I remember clearly infrom my childhood was harvesting sweet potatoes.

The way that "but" is used in this sentence doesn't make much sense. I would recommend:

I associate autumn with a deep sky, beautiful clouds and cool breeze, and it always brings back memories of sweet potato harvests from my childhood.

After heavy frost, the seedlings of the sweet potatoes died and it meant it was the harvest season ofor sweet potatoes.

Alternatively: "it meant it was sweet potato harvest season"

We followed the plow closely and picked ithem into our basket.

When the sweet potatoes harvesting season came, they were our fruits.

We just wiped the mud off the sweet potatoes and ate them.

It tasted good at thate time.

ItThey tastesd far yummyier than sweet potatoes and it was the first time I knew that there was something in the world that was moreally yummy than sweet potatoes.

Although I rarely eat sweet potatoes nowadays, I still remember that it iwas the sweet potatoes that feed me (as a child).

While not completely necessary, I would add the part in parentheses for clarity

Autumn is a nice season, especially when you just come fromin contrast to summer.

The original sentence does not really make any sense because autumn always comes after summer, so "when you just come from summer" is always true.

DHaving a deep sky, beautiful clouds, and a cool breeze is how I usually picture autumn, but one thing I remember clearly in my childhood was harvesting sweet potatoes.

I like the imagery of this sentence, but to make it work it needs a few things that the correction adds. The first part of the sentence needs to be contextualized/ needs a verb for what it is referring to, which I added with "is how I usually picture autumn". It also should contrast with the second half, because of the use of "but", which I added with "usually picture". There are many more ways to rewrite this to work grammatically, I just picked one that I think tries to capture your meaning while still mostly fitting the same structure.

After a heavy frost, the seedlings of the sweet potatoes died, and it meant it was the harvest season of sweet potatoes.

"harvest season of sweet potatoes" is not as concise as "sweet potato harvest season" and I think this ordering is somewhat more common in English, but either way works.

First we cut the seedlings off, and then we used one or two cows to pull a plow to harvest the sweet potatoes.

We followed the plow closely and picked itut them into our basket.

We were so excited when we saw a bigger one.

Here you do not need "bigger" because since you're already talking about only sweet potatoes, if you say a "big" one then the reader already knows its bigger than the other potatoes. It also sounds a little more natural/impactful this way.

Every harvest season we would choose the biggerst one for when our villagers to visited.

This is the only sentence where I'm not sure what you're trying to say. I tried to edit it to work grammatically. I think you want "biggest" here because it seems to be referring the the "most big" potato as the one you selected.

When the sweet potatoes harvesting season came, they were our fruits.

We just wiped the mud off sweet potatoes and ate them.

I think this sentence is stronger without "sweet potatoes" and the reader already knows what you are talking about. If you want to keep in "sweet potatoes" it should be "the sweet potatoes".

ItThey tastesd far yummyier than sweet potatoes and it was the first time I knew that there was something in the world that was reallyeven yummyier than sweet potatoes.

"realized" might fit better than "knew"