Za domem rośnie krzak z małymi białymi kwiatami.

Because za can take different cases depending on the meaning.

In this sentence, za domem means behind the house in a location sense, so Polish uses the instrumental case.

• za domem = behind the house / located behind the house
• za dom would usually suggest movement toward a position behind the house

Compare:

• Jest za domem. = It is behind the house.
• Idzie za dom. = He/she is going behind the house.

So here, since the bush is already growing in that location, za domem is correct.

Because dom is in the instrumental singular after za when it expresses location.

The noun dom changes like this:

• nominative: dom = house
• instrumental: domem

This is a very common pattern for masculine nouns:

• stół → stołem
• las → lasem
• dom → domem

So za domem literally means something like behind the house, with house in the instrumental form.

Rośnie comes from the verb rosnąć, which means to grow.

So:

• rośnie = grows / is growing

In this sentence it describes what the bush does:

• Za domem rośnie krzak = Behind the house, a bush grows / There is a bush growing behind the house.

In Polish, present tense can often cover both a general fact and something happening now, depending on context.

Because the subject is krzak (bush), which is singular and third person.

The verb rosnąć in the present tense goes like this:

• rosnę = I grow
• rośniesz = you grow
• rośnie = he/she/it grows
• rośniemy = we grow
• rośniecie = you all grow
• rosną = they grow

Since krzak is a singular thing, Polish uses rośnie.

Because krzak is the subject of the sentence, and subjects usually appear in the nominative case.

Here the sentence structure is basically:

• krzak rośnie = a bush grows

So krzak stays in its dictionary form, the nominative singular.

It literally means with small white flowers.

The preposition z here means with, and in this meaning it requires the instrumental case.

So all the words in that phrase are in the instrumental plural:

• kwiaty → kwiatami = flowers
• małe → małymi = small
• białe → białymi = white

This phrase describes the bush:

• krzak z małymi białymi kwiatami = a bush with small white flowers

Because they must agree with kwiatami in case, number, and gender.

Here:

• kwiatami is instrumental plural
• the adjectives describing it must also be instrumental plural

So:

• małe białe kwiaty = small white flowers (nominative/accusative plural)
• z małymi białymi kwiatami = with small white flowers (instrumental plural)

This agreement is a central feature of Polish grammar.

Both z and ze can mean with or from, but ze is usually used for easier pronunciation before certain consonant clusters.

Here z małymi is easy to pronounce, so plain z is used.

Compare:

• z domem = with the house
• ze szkoły = from school
• ze mną = with me

So in your sentence, z małymi białymi kwiatami is the normal form.

Polish word order is more flexible than English word order because grammatical endings show the roles of words.

So both of these are possible:

• Za domem rośnie krzak z małymi białymi kwiatami.
• Krzak z małymi białymi kwiatami rośnie za domem.

The version starting with Za domem puts the location first, which can sound natural if the speaker wants to set the scene: Behind the house...

So the word order here is normal and stylistically natural, not strange.

No. Za has several meanings depending on context and case.

Some common ones are:

• behind
  
  • za domem = behind the house
• for
  
  • dziękuję za pomoc = thank you for the help
• in exchange for
  
  • kupiłem to za 10 zł = I bought it for 10 zloty

So in this sentence, because of the location meaning and the instrumental case, za means behind.

Yes. Krzak can often be translated as bush or shrub.

• bush is usually the most natural everyday English translation
• shrub is a bit more formal or botanical

So both are possible depending on style.

Polish does not have articles like English a/an and the.

So krzak can mean:

• a bush
• the bush

The exact meaning depends on context.

In this sentence, English would usually say a bush unless the bush has already been mentioned.

A simple approximate pronunciation is:

Za DO-mem RO-shnye KSHAK z ma-WY-mi bya-WY-mi kfya-TA-mi

A few helpful points:

• rz in krzak sounds like the zh sound in measure, though pronunciation can vary depending on the word
• ś in rośnie is a soft sh-like sound
• cz / sz / rz / ż are important Polish consonant sounds to learn carefully
• ł sounds like English w
• w sounds like English v

So:

• małymi has ł pronounced like w
• kwiatami starts with something close to kvya-

It can mean either, depending on context.

Polish present tense often covers both:

• a general fact: A bush grows behind the house
• something currently happening: A bush is growing behind the house

In this sentence, English would usually translate it as a general description, but the Polish form itself does not force only one of those meanings.

Yes, you could, but it means something slightly different in emphasis.

• Za domem rośnie krzak... focuses on the fact that a bush grows there
• Za domem jest krzak... focuses more simply on the fact that there is a bush there

Both are grammatical. The original sentence sounds a bit more vivid and natural if you are describing plants or a garden scene.