huànpén yǐhòu, gēnbù zài yíngyǎngtǔ lǐ.

Yes. 以后 means after; later; following, and it often comes after a time word or an action phrase.

So:

• 换盆 = to change the pot / to repot
• 换盆以后 = after repotting

This pattern is very common:

• 吃饭以后 = after eating
• 下课以后 = after class
• 回家以后 = after going home / after returning home

So in this sentence, 换盆以后 sets the time frame: after repotting.

Chinese often omits the subject when it is obvious from context.

In a fuller sentence, you might have something like:

• 植物换盆以后，根部在营养土里。
• After the plant is repotted, the roots are in the potting soil.

But if the topic is already clear, Chinese commonly leaves it out. This is very natural.
So the sentence is not incomplete—it just relies on context more than English usually does.

根部 means the root part or the roots / root area.

Breakdown:

• 根 = root
• 部 = part; section

So 根部 is a slightly more anatomical or descriptive way to refer to the plant’s root section, rather than just the word 根 by itself.

Depending on context, it can be understood in English as:

• the roots
• the root area
• the root system (sometimes)

在 + place + 里 means to be in / inside somewhere.

Here:

• 在 = at / in
• 营养土里 = in the nutrient soil / in the potting soil

So:

• 根部在营养土里 = the roots are in the potting soil

This is a basic location pattern in Chinese:

• 书在桌子上。 = The book is on the table.
• 猫在房间里。 = The cat is in the room.
• 根部在营养土里。 = The roots are in the potting soil.

Literally, yes:

• 营养 = nutrition; nutrients
• 土 = soil

But in actual usage, 营养土 usually means nutrient-rich soil, potting soil, or planting mix, depending on context.

So you usually should not translate it too literally as nutrition soil in natural English.
A better translation is often:

• potting soil
• nutrient soil
• growing medium (in some contexts)

里 means inside. It makes the location sound complete and natural.

• 营养土里 = in the soil
• literally, inside the nutrient soil

In many cases, Chinese prefers adding 里 when something is physically inside an enclosed space, substance, or area.

Without 里, 根部在营养土 sounds incomplete or unnatural in most contexts.
So 在营养土里 is the normal phrasing.

Usually, 换盆以后 is enough and sounds natural.

Chinese often does not need 了 here, because 以后 already makes it clear that the repotting happens first and the next situation happens afterward.

• 换盆以后，根部在营养土里。 = natural
• 换盆了以后，根部在营养土里。 = possible in some contexts, but often less neat or less standard here

For learners, the safer pattern is:

• 动作 + 以后

Examples:

• 吃完以后
• 下班以后
• 换盆以后

Here it is a verb phrase: to change the pot / to repot.

Chinese verb phrases can often act a bit like English -ing forms or clauses when followed by time words such as 以后:

• 换盆以后 = after repotting
• 吃饭以后 = after eating
• 回家以后 = after going home

So even though English might use repotting as a gerund, Chinese simply uses the verb phrase directly.

Yes, 以后 can mean:

1. after something
2. from now on / in the future

The meaning depends on what comes before it.

Here, it follows an action phrase:

• 换盆以后 = after repotting

Compare:

• 以后再说。 = We’ll talk about it later.
• 大学毕业以后，他去了北京。 = After graduating from university, he went to Beijing.

So in this sentence, it clearly means after.

The comma separates the time phrase from the main statement.

Structure:

• 换盆以后， = after repotting,
• 根部在营养土里。 = the roots are in the potting soil.

This is very common in Chinese writing. The comma makes the sentence easier to read, especially when a time phrase comes first.

It would be much less natural in this context.

Chinese commonly puts time expressions early in the sentence:

• 换盆以后，根部在营养土里。

This matches the natural order:

• After repotting, the roots are in the soil.

You can move time expressions around in some cases, but with 以后 phrases like this, putting them at the front is usually the clearest and most natural choice.

Yes. This part describes a state/location, not an action.

• 在 here is not to be doing something
• it means to be located at/in

So the sentence says that after repotting, the roots are situated in the potting soil.

That is why there is no action verb like put or cover in this part. It is simply describing the condition or arrangement of the plant after repotting.