uekibati ni hiryou wo ireru.

It is read:

うえきばち に ひりょう を いれる

• 植木鉢 = うえきばち
• 肥料 = ひりょう
• 入れる = いれる

In normal Japanese writing, you would usually write it without spaces:

植木鉢に肥料を入れる。

に marks the destination/target location of the action here — the place something is being put into.

So in this sentence:

• 植木鉢に = into the flowerpot / in the flowerpot

With verbs like 入れる (to put in), the container or place receiving something is commonly marked by に.

を marks the direct object — the thing that is being acted on.

Here, the thing being put into the pot is 肥料.

So:

• 肥料を = fertilizer as the thing being put in

A simple way to see it is:

• 植木鉢に = where it goes
• 肥料を = what goes there

This is a very common question.

• 入れる（いれる） = to put something in
  
  • transitive
  • it takes an object marked by を
• 入る（はいる） = to enter / to go in
  • intransitive
  • it does not take a direct object with を

So:

• 植木鉢に肥料を入れる = put fertilizer into the flowerpot
• 肥料が植木鉢に入る = the fertilizer goes into the flowerpot / gets into the flowerpot

Because someone is actively putting the fertilizer in, 入れる is the correct verb here.

In this sentence, に is often translated as in or into, but it is not exactly the same as an English preposition.

Japanese particles do not match English prepositions one-to-one. Here, に marks the target location of the action. In natural English, that becomes in or into.

So it is fine to understand:

• 植木鉢に入れる = put into the flowerpot

But it is better to think of に as a Japanese grammar marker, not as a word that always equals one English preposition.

Japanese normally puts the verb at the end of the sentence.

So the basic order here is:

• 植木鉢に = into the flowerpot
• 肥料を = fertilizer
• 入れる = put

This is normal Japanese sentence structure. English and Japanese word order are different, so it is best not to expect a direct word-for-word match.

Yes, to some extent.

Because the particles に and を show the roles of the nouns, Japanese word order is more flexible than English. For example, these can both work:

• 植木鉢に肥料を入れる
• 肥料を植木鉢に入れる

Both mean essentially the same thing. The difference is mostly one of focus or natural flow in context.

However, the verb 入れる will usually stay at the end.

The subject is omitted.

Japanese very often leaves out the subject when it is obvious from context. So this sentence could mean:

• I put fertilizer in the flowerpot
• You put fertilizer in the flowerpot
• Someone puts fertilizer in the flowerpot
• Put fertilizer in the flowerpot (depending on context)

The exact subject is understood from the situation, not stated in the sentence itself.

入れる is in the dictionary form (plain non-past form).

This form can be used for several things depending on context, such as:

• a general statement
• a habitual action
• a casual statement
• a label/instruction style

Related forms would be:

• 入れます = polite form
• 入れた = past plain form
• 入れて = put in... / and put in...
• 入れない = negative plain form

So this sentence is in a basic plain form often used in dictionaries, examples, and simple statements.

Yes, but adding は changes the nuance.

For example:

• 肥料は植木鉢に入れる。
  As for the fertilizer, put it in the flowerpot.

• 植木鉢には肥料を入れる。
  In the flowerpot, one puts fertilizer. / At least in the flowerpot, fertilizer is put in.

Here, は adds topic or sometimes contrast. The original sentence with に and を is more neutral and straightforward.

Usually, に is the natural choice here.

• に marks the place something goes into
• で marks the place where an action happens, so it does not fit this meaning well
• へ mainly marks direction, and it is much less natural with a container like a flowerpot in this sentence

So:

• 植木鉢に肥料を入れる = natural
• 植木鉢で肥料を入れる = unnatural for this meaning
• 植木鉢へ肥料を入れる = possible to imagine in some contexts, but not the normal choice here

植木鉢（うえきばち） means flowerpot or plant pot.

It is made of:

• 植木（うえき） = plant / garden plant
• 鉢（はち / ばち in compounds） = pot, bowl, basin

So together, 植木鉢 is the pot that a plant grows in.

Yes. It is a perfectly natural simple sentence.

Without context, it sounds a little like:

• a basic example sentence
• an instruction step
• a textbook sentence

In real conversation, you might also hear polite or more contextual versions like:

• 植木鉢に肥料を入れます。
• 植木鉢に肥料を入れてください。
• 植木鉢に肥料を入れた。

But the original sentence is grammatically natural and very useful for learning.