Wkładam nasiona do małych doniczek, a potem podlewam je konewką.

Because Polish usually leaves the subject pronoun out when the verb already makes the person clear.

• wkładam = I put / I am putting
• podlewam = I water / I am watering

The ending -am shows 1st person singular, so ja is not necessary. You can add ja for emphasis, contrast, or clarity, but the neutral version usually omits it.

Wkładam is the 1st person singular present tense form of wkładać.

So it means:

• I put
• I am putting

It is also imperfective, which means it focuses on the action as ongoing, repeated, or not viewed as a single completed whole.

Its perfective partner is włożyć, for example włożę = I will put in / I will place in.

Because Polish present tense can describe:

• what someone is doing right now
• a habitual action
• a sequence of steps in a process

So Wkładam nasiona..., a potem podlewam je... can mean either:

• I’m putting the seeds in..., and then I water them...
• I put the seeds in..., and then I water them... as a regular procedure

In English, we often choose between simple present and present continuous more explicitly. Polish present tense is more flexible here.

Nasiona is the plural form of nasiono.

In this sentence, it is the direct object of wkładam, so it is in the accusative plural. For this noun, the accusative plural looks the same as the nominative plural:

• singular: nasiono
• plural: nasiona

So a learner may think nasiona is just the dictionary plural, but here it is also the correct object form.

Because the preposition do requires the genitive case.

So:

• basic form: małe doniczki
• after do: do małych doniczek

Breakdown:

• doniczki is from doniczka
• doniczek = genitive plural
• małych matches doniczek in case, number, and gender

This is very common in Polish:

• do domu = into the house
• do pudełka = into the box
• do małych doniczek = into small pots

Here a potem means something like and then or and afterwards.

The word a often connects two clauses in a way that feels like:

• and
• while
• whereas
• or a simple move to the next step

In this sentence, it helps the speaker move from one action to the next. It is very natural in Polish for step-by-step narration.

So:

• Wkładam nasiona do małych doniczek, a potem... = I put the seeds into small pots, and then...

You could sometimes use i potem, but a potem is especially common and natural in this kind of sequence.

Je is the pronoun them.

It refers back to nasiona. Instead of repeating the noun, Polish uses the object pronoun:

• podlewam nasiona = I water the seeds
• podlewam je = I water them

Here je is the correct accusative plural pronoun for a non-masculine-personal noun like nasiona.

So the structure is very similar to English:

• I water them

Sometimes yes, if the object is obvious from context, but in this sentence keeping je is the most natural choice.

Without it, a potem podlewam konewką would sound incomplete unless the listener already strongly understands what is being watered.

So podlewam je konewką is a normal, clear sentence:

• podlewam = I water
• je = them
• konewką = with a watering can

Because konewką is the instrumental singular form of konewka.

Polish often uses the instrumental case to show the tool or means used to do something:

• piszę długopisem = I write with a pen
• jadę autobusem = I go by bus
• podlewam konewką = I water with a watering can

So:

• basic form: konewka
• instrumental: konewką

That final -ą is a very common instrumental singular ending.

No, Polish word order is fairly flexible, but the version you have is natural and neutral.

Wkładam nasiona do małych doniczek, a potem podlewam je konewką sounds like a straightforward description of actions.

You can move things around for emphasis, for example:

• Nasiona wkładam do małych doniczek... emphasizes nasiona
• Potem podlewam je konewką emphasizes then
• Konewką podlewam je sounds more marked and emphasizes the tool

So the meaning stays similar, but the focus changes. The original sentence is a very normal default order.