Podmiska je pod květináčem.

Because pod takes different cases depending on meaning.

In Podmiska je pod květináčem, pod means location (under), so it requires the instrumental case.
The noun květináč therefore changes to květináčem.

• nominative: květináč = flowerpot
• instrumental: květináčem = under/with the flowerpot, depending on context

So after pod for a stationary position, květináčem is the correct form.

You use pod květináč when there is movement toward a position under something, not just location.

So:

• pod květináčem = under the flowerpot (already there)
• pod květináč = to under the flowerpot / under the flowerpot as a destination

Example:

• Podmiska je pod květináčem. = The saucer is under the flowerpot.
• Dám papír pod květináč. = I’ll put the paper under the flowerpot.

This is a very common Czech pattern with prepositions:
location = one case, movement = another case.

Podmiska is in the nominative case because it is the subject of the sentence — the thing being talked about.

You can identify it by asking What is under the flowerpot?
Answer: podmiska.

So the structure is:

• Podmiska = subject, nominative
• je = is
• pod květináčem = prepositional phrase describing location

Je is the 3rd person singular form of být (to be), meaning is.

Czech often omits to be in the present tense only in some special styles, headlines, or very informal notes, but in a normal full sentence like this, je is standard and expected.

So:

• Podmiska je pod květináčem. = normal complete sentence
• Podmiska pod květináčem. = sounds incomplete in ordinary speech, more like a label or note

Czech has no articles. There is no direct equivalent of English a/an or the in ordinary usage.

So Podmiska je pod květináčem could mean:

• The saucer is under the flowerpot
• A saucer is under a flowerpot

Which one is meant depends on context.

If Czech speakers need to make it more specific, they usually do it with word order, context, or words like:

• ta podmiska = that/the saucer
• nějaká podmiska = some/a saucer

Yes. Czech word order is quite flexible, because case endings show the grammatical role.

The neutral order here is:

• Podmiska je pod květináčem.

But you could also say:

• Pod květináčem je podmiska.

That still means the same thing, but the emphasis changes a little:

• Podmiska je pod květináčem. → talking about the saucer
• Pod květináčem je podmiska. → focusing more on the location

So the meaning stays basically the same, but the sentence focus shifts.

Yes. Podmiska is a feminine noun.

A good clue is the ending -a, which often marks feminine nouns in Czech.

You can see that in agreement:

• ta podmiska = the/that saucer
• malá podmiska = small saucer

This matters when you use adjectives, pronouns, or past-tense forms.

Roughly like kvye-ti-naa-chem, though not exactly in English sounds.

A few important points:

• kvě sounds roughly like kvye
• á is a long vowel
• č sounds like ch in church
• ch in Czech is not English ch; it is a throaty sound like in German Bach or Scottish loch

So květináčem is approximately:

k-vye-ti-NAA-chem

The stress in Czech is almost always on the first syllable, so the stress is on kvě.

Because podmiska is a separate noun, and its form is historically connected with something that goes under a pot or container. So yes, it contains the element pod-.

But in the sentence, the second pod is the actual preposition meaning under.

So these are two different things:

• podmiska = a noun meaning saucer / drip tray
• pod = the preposition under

It may sound repetitive to an English speaker, but in Czech it is completely natural.

In this sentence, because of květináčem (flowerpot), podmiska clearly means a plant saucer / drip tray — the dish placed under a flowerpot to catch water.

In other contexts, podmiska can also mean a saucer more generally, but with plants this gardening meaning is the natural one.

So here the most idiomatic understanding is plant saucer.

Yes, it is natural and correct Czech.

A native speaker could also say:

• Pod květináčem je podmiska.

That may sound a bit more natural in some contexts if the location is the main point. But Podmiska je pod květináčem is absolutely fine and grammatical.

So as a learner, you can safely use this sentence.