Если не поливать орхидею вовремя, её стебель слабеет, а бутон может засохнуть.

Because орхидею is the accusative singular form of орхидея.

The verb поливать means to water, and the thing being watered is the direct object, so it takes the accusative case:

• nominative: орхидея = orchid
• accusative: орхидею = orchid as the object of the action

So:

• поливать орхидею = to water the orchid

This is very common with verbs that act directly on something.

Поливать is the imperfective verb, while полить is perfective.

Here, Russian uses поливать because the sentence describes a general condition or repeated/habitual situation:

• Если не поливать орхидею вовремя... = If the orchid is not watered on time / If you do not water the orchid on time

The idea is not one single completed act of watering, but the general practice of watering it properly.

Very roughly:

• поливать = to water, to be watering, to water regularly
• полить = to water once, to complete the watering

In an if statement about general truth or regular care, the imperfective is the natural choice.

Russian often uses an infinitive like this to make a statement feel general or impersonal.

So Если не поливать орхидею вовремя literally looks like:

• If not to water the orchid on time

But naturally it means:

• If you don’t water the orchid on time
• If one does not water the orchid on time
• If the orchid is not watered on time

English usually needs a subject, but Russian can leave it general and understood from context.

This is a common pattern when talking about instructions, habits, or general consequences.

Вовремя means on time or in time.

It is an adverb, and in modern Russian it is written as one word:

• вовремя

It modifies the verb поливать:

• поливать вовремя = to water on time

This word is very common in everyday Russian:

• приходить вовремя = to arrive on time
• сделать вовремя = to do something in time

Here её is a possessive pronoun meaning her or its, depending on context.

Since орхидея is a plant, English would normally say its stem, but Russian uses её because орхидея is a feminine noun.

So:

• её стебель = its stem

A useful point: this form её does not change here. Russian often uses:

• его = his / its
• её = her / its
• их = their

So even though стебель is masculine, the pronoun refers back to орхидея, which is feminine.

Because стебель is the subject of the verb слабеет.

In Russian, the subject is usually in the nominative case, which is the dictionary form:

• стебель = stem

So:

• её стебель слабеет = its stem weakens / becomes weaker

Even though её comes before it, стебель is still the main noun acting as the subject of the clause.

Russian often uses the present tense to express general truths, regular results, or what happens in such cases.

So слабеет here does not mean only is weakening right now. It means something more like:

• becomes weak
• grows weaker
• weakens

This is very common in Russian:

• Если много есть, человек толстеет.
  • If a person eats a lot, they gain weight.

So слабеет is present tense, but it describes a typical consequence.

In this sentence, а introduces a second, contrasting or additional result:

• её стебель слабеет, а бутон может засохнуть

Here, а is not a strong contradiction. It is more like:

• while
• and
• and meanwhile
• whereas

It helps separate two related consequences:

1. the stem weakens
2. the bud may dry up

If you used но, it would sound more like a stronger but, as if the second part opposed the first. That is not the idea here. The sentence is listing two different negative outcomes, so а works better.

Засохнуть is perfective, and засыхать is imperfective.

After может, Russian often chooses the aspect based on the meaning:

• может засохнуть = may dry up, may end up dried out
• может засыхать = may be drying up, may tend to dry up, may dry up repeatedly

Here the sentence focuses on the possible result: the bud may reach the state of being dried out. That is why засохнуть is natural.

So:

• бутон может засохнуть = the bud may dry up

The perfective infinitive points to the outcome.

Because its subject is бутон, which is singular:

• бутон = bud

So the verb must also be singular:

• бутон может = the bud can / may

If the subject were plural, the verb would change:

• бутоны могут = the buds can / may

There are two main punctuation points here.

1. After вовремя

   • Если не поливать орхидею вовремя, ...

   This comma separates the if-clause from the main clause. Russian normally uses a comma after a subordinate clause introduced by если.

2. Before а

   • ..., её стебель слабеет, а бутон может засохнуть.

   This comma separates two coordinated clauses joined by а.

So the structure is:

• Если ... , [main clause 1], а [main clause 2].

Yes, Russian word order is fairly flexible, though the original version sounds natural and neutral.

For example, you could also say:

• Если орхидею не поливать вовремя, её стебель слабеет, а бутон может засохнуть.

This version puts орхидею before не поливать, but the meaning stays the same.

The original:

• Если не поливать орхидею вовремя...

sounds slightly more general and smooth, especially in instructions or explanations about plant care.