hatizokoisi de mizuhake ga yoku naru.

鉢底石 refers to the small stones or gravel placed at the bottom of a flowerpot or planter.

It is a compound noun:

• 鉢 = pot
• 底 = bottom
• 石 = stone

So literally it is something like pot-bottom stones.

It is read はちぞこいし.

A learner might expect そこ for 底, but in this compound it becomes ぞこ, which is a common sound change in Japanese compounds.

Here, で shows the means, material, or thing used to produce a result.

So 鉢底石で means something like:

• with drainage stones
• by using drainage stones
• because of drainage stones in a practical sense

It does not mean location here.

So the sentence structure is basically:

• 鉢底石で = using drainage stones
• 水はけがよくなる = drainage becomes good / improves

No. In this sentence, で is not marking a place where something happens.

Japanese で has several uses, and one very common one is means/method:

• バスで行く = go by bus
• ナイフで切る = cut with a knife

This sentence uses that same idea:

• 鉢底石で = with / by using drainage stones

水はけ means drainage or how well water drains.

It is read みずはけ.

This is a set expression. Even if you know:

• 水 = water
• はけ is less obvious on its own

you should learn 水はけ as a vocabulary item meaning drainage.

Examples:

• 水はけがいい = drainage is good
• 水はけが悪い = drainage is bad

が marks 水はけ as the thing that changes or has the property being described.

In 水はけがよくなる:

• 水はけ = drainage
• が = marks it as the subject
• よくなる = becomes good / gets better

So the sentence is focusing on drainage as the thing that improves.

If you used は, the nuance would shift more toward topic/contrast:

• 水はけはよくなる = as for drainage, it gets better

That is possible in some contexts, but が is the more natural default here.

Because なる combines with the adverb form of an adjective.

The adjective is:

• いい or よい = good

Its adverb form is:

• よく = well

So:

• よくなる = become good / become better / improve

This is a very common pattern:

• 高い → 高くなる = become expensive / higher
• 早い → 早くなる = become early / faster
• よい → よくなる = become good / better

So よくなる is grammatically the correct form.

It can mean either, depending on context.

Literally, it is become good, but in natural English it is often better translated as:

• gets better
• improves

So 水はけがよくなる is very naturally:

• drainage improves
• water drains better

Yes, you can feel that idea in the background.

A fuller sentence might be:

• 鉢底石を入れると、水はけがよくなる。
  • If you put drainage stones in, drainage improves.

But Japanese often allows a shorter expression when the relationship is clear.

So 鉢底石で水はけがよくなる is a compact way of saying that using or adding drainage stones improves drainage.

Yes. It sounds like a general statement or practical explanation, such as in gardening instructions.

There is no explicit subject like this pot or the soil, so it has a broad, general feel:

• Using drainage stones improves drainage.

Japanese often leaves out subjects when they are obvious or unnecessary.

Yes. Depending on the context, several natural translations are possible:

• Using drainage stones improves drainage.
• Drainage gets better with drainage stones.
• Adding stones to the bottom of the pot improves drainage.
• Water drains better with pot-bottom stones.

The Japanese is short and compact, so English may need to be a little more explicit to sound natural.

The core pattern is:

Noun + で + Noun + が + adjective-adverb + なる

In this sentence:

• 鉢底石 = noun
• で = by/with/using
• 水はけ = noun
• が = subject marker
• よく = adverb form of いい / よい
• なる = become

So the structure is:

By using X, Y becomes good/better.

That is a very useful pattern to remember.