syokubutu no seityou wo kakuninsita.

It is read:

しょくぶつ の せいちょう を かくにんした。

Word by word:

• 植物 = しょくぶつ
• の
• 成長 = せいちょう
• を
• 確認した = かくにんした

Also, the spaces are just for learning. In normal Japanese writing, it would usually be written as:

植物の成長を確認した。

Here, の links two nouns.

• 植物 = plant(s)
• 成長 = growth

So 植物の成長 means the growth of the plant(s) or plant growth.

A helpful way to think about A の B is:

• B of A
• A's B
• sometimes simply A B in natural English

So:

• 植物の成長 = the growth of plants / plant growth

を marks the direct object of the verb.

The verb here is 確認した, which means confirmed, checked, or verified.

So the thing being confirmed is:

• 植物の成長

That is why it becomes:

• 植物の成長を確認した。
• (Someone) confirmed the plants' growth.

In other words:

• 何を確認した？ = What did (someone) confirm?
• 植物の成長を = the plants' growth

成長 can function as a noun, meaning growth.

So in this sentence:

• 植物の成長 = the growth of the plants

There is also a related verb:

• 成長する = to grow / to develop

Compare:

• 植物の成長を確認した。
  = Confirmed the plants' growth.

• 植物が成長した。
  = The plants grew.

The first sentence focuses on confirming the growth.
The second sentence simply states that the plants grew.

確認した is the plain past form of 確認する.

• 確認する = to confirm / to check
• 確認した = confirmed / checked

This tells you the action happened in the past.

So the sentence means that someone confirmed it, not that they are confirming it right now.

If it were present/non-past:

• 植物の成長を確認する。
  = confirm / will confirm the plants' growth

Japanese often leaves out the subject when it is obvious from context or not important.

So 植物の成長を確認した。 does not explicitly say who did the confirming.

Depending on context, it could mean:

• I confirmed the plants' growth.
• We confirmed the plants' growth.
• They confirmed the plants' growth.
• Someone confirmed the plants' growth.

This is very normal in Japanese. If the subject matters, it can be added, for example:

• 私は植物の成長を確認した。 = I confirmed the plants' growth.

By itself, 植物 can mean a plant, plants, or plant life, depending on context.

Japanese nouns usually do not show singular/plural clearly the way English does.

So 植物の成長 could mean:

• the growth of a plant
• the growth of plants

You decide from the situation.

If someone wanted to make it clearer, they might use a more specific word like:

• この植物 = this plant
• 植物たち = plants
• 複数の植物 = multiple plants

But in many cases, plain 植物 is enough.

Not exactly.

確認した has the nuance of:

• checked
• confirmed
• verified
• made sure of

It sounds more deliberate than simply seeing something.

For example:

• 見た = saw
• 観察した = observed
• 確認した = checked/confirmed

So 植物の成長を確認した suggests that someone looked and made sure that growth had occurred. It can sound a bit objective or report-like.

Yes, and it is slightly more explicit.

• 植物の成長を確認した。
• 植物が成長したことを確認した。

The second version literally means:

• confirmed that the plants grew

The first version is more compact:

• confirmed the plants' growth

Both are natural, but the first one is shorter and a bit more noun-based, while the second spells out the event more clearly with こと.

It is in the plain past style, so it is neutral and often used in:

• writing
• reports
• diaries
• casual narration

The polite version would be:

植物の成長を確認しました。

That would be more appropriate in polite conversation, formal reporting to someone, or business situations.

So:

• 確認した = plain
• 確認しました = polite