Learn Hardcore Polish: Wieczorem podlewam rośliny na parapecie, bo słońce świeciło cały dzień. - In the evening I water the plants on the windowsill, because the sun shone all day.

Wieczorem comes from the noun wieczór (evening) in a form that functions as an adverbial of time. Literally it’s the instrumental case „(in) the evening”, but in practice it just means „in the evening” / „at night (in the evening)”.

Polish very often uses bare time words (usually in instrumental) without a preposition to mean „at that time”:

Rano – in the morning
Po południu – in the afternoon (here with a preposition)
Wieczorem – in the evening
Nocą – at night

You could say „wieczorem podlewam” or „podlewam wieczorem” – word order is flexible. But you normally don’t say „w wieczór podlewam”; that sounds unnatural in modern Polish.

Why is „podlewam” in the present tense? In English we also say „I water” for a habit, but could it mean „I am watering (right now)” too?

Podlewam is 1st person singular, present tense, imperfective, from podlewać (to water, repeatedly / as a process).

Polish present tense of an imperfective verb covers both:

habitual:
- Wieczorem podlewam rośliny – I (usually) water the plants in the evening.
right-now, ongoing:
- Teraz podlewam rośliny – I am watering the plants (right now).

So podlewam here can be understood as:

a habitual routine (what I normally do in the evenings), or
a current arrangement / what I’m doing this particular evening (depending on context).

Spoken context and intonation usually make it clear.

What is the difference between „podlewać” and „podlać”? Why is the imperfective „podlewam” used here?

Polish verbs come in aspect pairs:

podlewać – imperfective (ongoing, repeated, process)
- present: podlewam, podlewasz, podlewa…
- past: podlewałem / podlewałam etc.
podlać – perfective (single, completed action)
- future only: podleję, podlejesz, podleje…
- past: podlałem / podlałam etc.

In this sentence:

podlewam (imperfective present) fits because we’re talking about an activity (watering) as an ongoing or typical action, not about a single completed event.

Compare:

Wieczorem podlewam rośliny. – In the evening I (usually) water the plants.
Wieczorem podleję rośliny. – In the evening I will (once, specifically) water the plants.

Why is it „rośliny” and not something like „roślinę” or „roślinki”? What case is it?

The base noun is roślina – a plant.

Rośliny here is:

plural
accusative case
used as the direct object of the verb podlewam.

Declension (simplified, singular → plural):

Nominative (who/what?): roślina → rośliny
Accusative (direct object): roślinę → rośliny

Masculine inanimate and most neuters share nominative/accusative forms, but feminine nouns like roślina change in the singular:

Widzę roślinę. – I see a plant. (sg acc.)
Widzę rośliny. – I see plants. (pl acc.)

Here podlewam rośliny = I water the plants.

Why do we say „na parapecie” and not „na parapet”? What form is „parapecie”?

Parapet = windowsill.

Na parapecie uses:

preposition na (on), indicating location (where?),
parapecie – locative singular of parapet.

With static location (on, in, at where something is), na takes the locative:

na stole – on the table
na krześle – on the chair
na parapecie – on the windowsill

With movement onto / to a surface, na takes the accusative:

kładę książkę na stół – I put the book onto the table.

Here, the plants are located on the windowsill:
rośliny na parapecie – plants on the windowsill.

Why is there a comma before „bo”? Is it obligatory?

Yes, in standard Polish punctuation it is obligatory.

Bo (because) introduces a subordinate clause that gives the reason:

Wieczorem podlewam rośliny na parapecie, bo słońce świeciło cały dzień.
- Main clause: Wieczorem podlewam rośliny na parapecie
- Subordinate reason clause: bo słońce świeciło cały dzień

Polish usually puts a comma before conjunctions that introduce subordinate clauses:

bo (because)
że (that)
ponieważ (because)
kiedy (when), etc.

So the comma here is a straightforward application of that rule.

Why is it „słońce świeciło” and not „świecił”? What governs this form?

Słońce (the sun) is neuter singular in Polish.

In the past tense, the verb must agree in gender and number with the subject:

masculine: świecił
feminine: świeciła
neuter: świeciło
plural: świeciły / świecili (depending on the group)

So with neuter słońce, the correct past form is:

słońce świeciło – the sun was shining / shone.

Świecił would be used with a masculine noun, e.g.:

lampion świecił – the lantern was shining.

Why is the second clause in the past tense („słońce świeciło cały dzień”) if the first clause uses present („podlewam”)? Is that normal in Polish?

Yes, this combination is natural and meaningful.

Wieczorem podlewam rośliny na parapecie – describes what I am doing this evening (or what I typically do in the evenings).
bo słońce świeciło cały dzień – explains the cause that occurred earlier that same day in the past.

So the idea is:

This evening I’m watering the plants on the windowsill, because earlier today the sun shone all day.

The present situates your watering in the current time frame.
The past describes something that already happened and led to the current situation.

If you wanted a purely general, timeless reason, you might also hear:

Wieczorem podlewam rośliny, bo słońce świeci cały dzień latem.
– I water the plants in the evening because the sun shines all day in summer.

There both clauses are in a kind of generalized present.

What does „świeciło” exactly express here? Why not a perfective verb?

Świeciło is:

past tense,
imperfective,
from świecić – to shine, to be shining.

Imperfective in the past is used for:

ongoing, continuous actions in the past,
background situations,
duration.

So słońce świeciło cały dzień emphasizes:

the duration: it was shining throughout the whole day.
the process, not the single moment of starting or stopping.

A perfective option (e.g. zaświecić, to start shining) would focus on a single event:

Słońce zaświeciło – The sun lit up / started to shine.

That would change the meaning; you’d lose the idea of “all day long”.

Why is it „cały dzień” and not „cała dzień” or „cały dniem”?

Dzień (day) is masculine singular.

Cały is an adjective meaning whole / entire, and it must agree with dzień in:

gender: masculine,
number: singular,
case: here accusative.

In Polish, the accusative masculine inanimate form is usually the same as the nominative:

Nominative: cały dzień (the whole day)
Accusative: cały dzień (for the whole day)

The phrase cały dzień without a preposition is a common way to express duration: “for the whole day / all day long”.

Świeciło cały dzień. – It was shining all day (long).

Cała dzień is incorrect (wrong gender), and cały dniem would be instrumental case, which does not fit here.

Why does the sentence start with „Wieczorem” instead of „Podlewam wieczorem…”? Does that change the meaning?

Polish word order is relatively flexible. Both are grammatically fine:

Wieczorem podlewam rośliny na parapecie, bo…
Podlewam rośliny na parapecie wieczorem, bo…

Starting with Wieczorem:

puts extra emphasis on the time frame (“In the evening, that’s when I water…”),
sounds slightly more natural and fluent in this particular sentence.

Changing the order does not change the basic meaning; it only shifts the focus a bit, similar to:

In the evening, I water the plants…
vs.
I water the plants in the evening…