Tôi bón trước khi tưới.

Here, bón means to apply fertilizer to plants or soil.

In gardening or farming Vietnamese, bón is very commonly used in expressions like:

• bón phân = to fertilize
• bón cây = to fertilize plants, though bón phân cho cây is clearer

So in this sentence, bón is understood as something like fertilize or apply fertilizer.

Because Vietnamese often leaves out words that are obvious from context.

A fuller version would be:

• Tôi bón phân trước khi tưới.

But if everyone already knows you are talking about caring for plants, just saying bón is natural.

So this sentence is a bit like English I fertilize before watering where the plants is also left unstated.

Trước khi means before.

It introduces the action that comes later in time.

Structure:

• [main action] + trước khi + [other action]

So here:

• Tôi bón = I fertilize
• trước khi tưới = before watering

The order of words matches the order of ideas:

• first action mentioned: bón
• second action mentioned after trước khi: tưới

Again, the object is omitted because it is understood from context.

Depending on the situation, the full meaning could be:

• tưới cây = water the plants
• tưới nước = water, give water
• tưới cho cây = water the plants

So tưới by itself is often enough when the listener already knows what is being watered.

By itself, it does not have a marked tense.

Vietnamese often leaves tense unstated unless it needs to be made clear. So Tôi bón trước khi tưới could mean:

• a habit: I fertilize before watering
• a present plan: I am fertilizing before watering
• a past action, if the context shows it
• a future action, if the context shows it

If you want to make time clearer, Vietnamese can add words like:

• đã = past
• đang = ongoing
• sẽ = future

For example:

• Tôi đã bón trước khi tưới.
• Tôi sẽ bón trước khi tưới.

Yes, very often.

If the subject is already clear from context, a speaker may simply say:

• Bón trước khi tưới.

That can sound like:

• a note to oneself
• a general instruction
• an informal statement where the subject is obvious

But tôi is kept when the speaker wants to be clear that I am the one doing it.

Yes, that is also grammatical and natural.

Compare:

• Tôi bón trước khi tưới.
  This starts with I fertilize and then adds the time relationship.

• Trước khi tưới, tôi bón.
  This starts with before watering, so it emphasizes the sequence first.

Both mean the same basic thing. The difference is mainly emphasis and style.

Almost.

• tưới = to water, to sprinkle, to irrigate
• tưới nước = to water with water, more explicit

In many plant-care contexts, tưới alone is enough because water is already understood.

So:

• Tôi bón trước khi tưới.
• Tôi bón trước khi tưới nước.

Both work, but the first is a little shorter and more conversational if the context is clear.

It is natural if the context is already clear.

A more explicit version would be:

• Tôi bón phân trước khi tưới cây.

That version is helpful if you want to state everything clearly. But in real conversation, Vietnamese often drops predictable words, so the shorter sentence sounds normal in the right context.

A rough breakdown is:

• Tôi — ngang tone
• bón — sắc tone
• trước — sắc tone
• khi — ngang tone
• tưới — sắc tone

A few useful pronunciation points:

• tr in trước is a Vietnamese consonant cluster that English speakers often need practice with.
• ư in trước and tưới is not an English vowel, so it may feel unfamiliar.
• tưới and trước both contain vowel combinations that are harder than they look if you are new to Vietnamese.
• The rising sắc tone on bón, trước, and tưới is important for being understood.

If you want to sound natural, it helps to practice the whole sentence as one rhythm group:

• Tôi bón trước khi tưới.