Poté co dám substrát do květináče, přesadím rostlinu.

In Czech, perfective verbs often use their present-tense forms to express the future.

• dám = I will put / I will place
• přesadím = I will transplant / repot

These are not present in meaning here. They refer to a completed action in the future.

This is very different from English. In Czech:

• dávám = I am putting / I put habitually (imperfective, true present)
• dám = I will put once, to completion (perfective, future meaning)

Likewise:

• přesazuji = I am transplanting / I transplant regularly
• přesadím = I will transplant once, successfully/fully

So the sentence describes a sequence of future completed actions.

Because the sentence is about one completed action followed by another completed action.

• First: dám substrát do květináče = I put the substrate into the pot
• Then: přesadím rostlinu = I transplant the plant

The focus is on reaching the result of each action, not on the process itself. That is exactly what perfective aspect does.

If you used imperfective verbs, the meaning would change:

• Poté co dávám substrát... sounds wrong here, because it suggests an ongoing process rather than a completed step.
• Poté co přesazuji rostlinu... would also not fit the intended sequence.

With poté co in a sentence like this, Czech naturally uses perfective verbs when the idea is after X is done, Y will happen.

Yes. Poté co means after, after the point when, or once in this context.

So:

• Poté co dám substrát do květináče, přesadím rostlinu.
• After I put the substrate into the flowerpot, I will transplant the plant.

A few close alternatives are:

• potom co = after
• až = when / once / after, depending on context
• jakmile = as soon as

Poté co is a bit more neutral or slightly more formal than potom co.

Because Czech usually omits subject pronouns when the verb ending already makes the subject clear.

Here:

• dám clearly means I will put
• přesadím clearly means I will transplant

So já is unnecessary.

You could say:

• Poté co já dám substrát do květináče, přesadím rostlinu.

But that would usually sound emphatic, as if you were stressing I in contrast to someone else.

In normal Czech, leaving out já is the standard choice.

Substrát is the direct object of dám, so it is in the accusative case.

However, substrát is a masculine inanimate noun, and in the singular, the accusative often looks the same as the nominative.

So:

• nominative: substrát
• accusative: substrát

That is why there is no visible ending change.

This is very common with masculine inanimate nouns in Czech.

Because rostlinu is the accusative singular of rostlina.

• rostlina = nominative singular = plant as the subject
• rostlinu = accusative singular = plant as the object

In this sentence, the plant is what is being transplanted, so it must be in the accusative:

• přesadím rostlinu = I will transplant the plant

This is a very typical feminine noun pattern:

• nominative: -a
• accusative: -u

The preposition do takes the genitive case and usually expresses movement into something.

So:

• do = into / to
• květináč = flowerpot
• do květináče = into the flowerpot

Here the noun changes to genitive singular:

• nominative: květináč
• genitive: květináče

This is used because the sentence describes movement of the substrate into the pot.

Compare:

• v květináči = in the flowerpot (location, locative)
• do květináče = into the flowerpot (direction, genitive)

Here it is singular: into the flowerpot.

The base noun is:

• květináč = flowerpot

After do, it becomes genitive singular:

• do květináče

So the sentence means putting the substrate into one pot, not multiple pots.

Because Czech uses a comma to separate a subordinate clause from the main clause.

Here:

• Poté co dám substrát do květináče = subordinate clause
• přesadím rostlinu = main clause

So the comma marks the boundary between them:

• Poté co dám substrát do květináče, přesadím rostlinu.

That comma is required.

You may also see Poté, co... with an extra comma after Poté in some writing styles. But the most important comma is the one separating the two clauses.

Yes. Czech word order is quite flexible, although the original version is perfectly natural.

You could also say:

• Přesadím rostlinu poté co dám substrát do květináče.

This means essentially the same thing:
I will transplant the plant after I put the substrate into the flowerpot.

The version with the time clause first:

• Poté co dám substrát do květináče, přesadím rostlinu.

puts more emphasis on the sequence of steps.

Czech often changes word order for focus, rhythm, or style, more than English does.

Yes, substrát is a correct word, especially in gardening or horticultural contexts. It means something like growing medium, potting substrate, or potting mix.

In everyday speech, people might also say:

• zemina = soil
• hlína = dirt/soil (more informal, not always technically precise)

So depending on context:

• dám substrát do květináče sounds a bit more technical or gardening-specific
• dám zeminu do květináče sounds very natural in everyday speech

All are possible, but substrát is absolutely fine.

It can mean both, depending on context.

The verb přesadit means to move a plant from one place/container to another. In English, that might be:

• transplant
• repot
• sometimes replant

Because the sentence mentions květináč (flowerpot), repot the plant is often the most natural English interpretation.

So:

• přesadím rostlinu = I will transplant/repot the plant

Both are reasonable translations.

Yes, that is possible, but it feels a little different.

• Poté co... = after
• Až... = when / once / after, often with a stronger sense of “when that moment comes”

So:

• Poté co dám substrát do květináče, přesadím rostlinu.
• Až dám substrát do květináče, přesadím rostlinu.

Both can work, but poté co more directly matches English after, while až is a very common Czech way to express future sequence more generally.

A learner should recognize both, but the original sentence is completely natural.