Kořenový bal je nad drenážní vrstvou.

Word by word:

• kořenový = root / root-related
• bal = ball, clump, or root ball in gardening context
• je = is
• nad = above, over
• drenážní = drainage
• vrstvou = layer (in a changed form; the basic dictionary form is vrstva)

So the sentence is literally:

root ball is above drainage layer

In natural English, that would usually be The root ball is above the drainage layer.

Because after nad in this sentence, Czech uses the instrumental case to show location.

• dictionary form: vrstva = layer
• instrumental singular: vrstvou

So:

• nad vrstvou = above the layer

This is one of the first big differences from English: Czech changes noun endings depending on their role in the sentence.

The preposition nad can take two different cases depending on meaning:

• instrumental = location, position
  
  • je nad drenážní vrstvou = it is above the drainage layer
• accusative = movement toward/over a position
  
  • for example, dát něco nad vrstvu = to put something above the layer

So in your sentence, nothing is moving. It just describes where the root ball is. That is why Czech uses instrumental.

It is in the nominative case, because it is the subject of the sentence.

• Kořenový bal = the thing that is somewhere
• je agrees with that subject
• nad drenážní vrstvou tells us where it is

So the sentence structure is:

• Kořenový bal = subject
• je = verb
• nad drenážní vrstvou = prepositional phrase showing location

Because kořenový is an adjective meaning root-related or of roots.

In Czech, this is the normal way to form many technical or descriptive phrases:

• kořen = root
• kořenový = root / root-related
• kořenový bal = root ball

Using kořen bal would sound unnatural here. Czech prefers the adjective form.

Because kořenový is an adjective agreeing with bal.

Bal is:

• masculine
• singular
• inanimate
• nominative here

So the adjective also has to match that noun. The form kořenový is the correct nominative singular masculine inanimate form.

This agreement is a core feature of Czech grammar: adjectives change to match the noun they describe.

Because drenážní is a different type of adjective.

It belongs to the soft adjective pattern, and in many forms its ending stays -í. So even when the noun changes case, the adjective may look the same.

Here:

• basic form: drenážní vrstva
• instrumental singular: drenážní vrstvou

The noun clearly changes from vrstva to vrstvou, but the adjective drenážní stays the same in form.

That is normal.

A rough pronunciation guide for an English speaker:

• Kořenový ≈ KO-rzhe-no-vee
• bal ≈ bahl
• je ≈ yeh
• nad ≈ naht
• drenážní ≈ dreh-NAHZH-nee
• vrstvou ≈ VERST-voh

A few important points:

• ř is a special Czech sound, something like a mix of r and zh. It is difficult for learners.
• ž sounds like the s in measure.
• á is a long vowel.
• ou is like oh
  • oo said together quickly.

You do not need perfect ř immediately; learners often approximate it at first.

Yes. Czech normally has no articles.

So:

• Kořenový bal can mean a root ball or the root ball
• drenážní vrstvou can mean a drainage layer or the drainage layer

The exact meaning depends on context.

In English, articles are required. In Czech, they usually are not.

Yes, Czech word order is more flexible than English because cases show grammatical roles.

The neutral order here is:

Kořenový bal je nad drenážní vrstvou.

But other orders are possible, especially for emphasis, for example:

• Nad drenážní vrstvou je kořenový bal.

That still means essentially the same thing: Above the drainage layer is the root ball.

The difference is mostly one of emphasis or style, not basic meaning.

It exists as a normal Czech word, but in this sentence it is being used in a technical/gardening expression: kořenový bal.

In that phrase, it means the compact mass of roots and soil around a plant’s roots — exactly what English calls a root ball.

So even if bal on its own may not always be common in everyday conversation, the full phrase kořenový bal is a standard gardening term.

No. Nad drenážní vrstvě is not correct here.

After nad expressing location, Czech needs the instrumental, not the dative or locative.

Correct:

• nad drenážní vrstvou

Incorrect:

• nad drenážní vrstvě

This is a very common learner issue, because English prepositions do not force noun endings in the same way.

The pattern is:

[subject in nominative] + [form of být = to be] + [nad + instrumental]

So here:

• Kořenový bal = subject in nominative
• je = is
• nad drenážní vrstvou = location phrase

You can reuse this pattern in many other sentences, for example:

• Květináč je nad podlahou. = The flowerpot is above the floor.
• Police je nad stolem. = The shelf is above the table.

It is a very useful structure to learn.