التربة رطبة منذ أن سقى صديقي النبات المنزلي.

In Arabic, the present tense of to be is usually not written or spoken.

So:

• التربة رطبة = The soil is moist

This is called a nominal sentence. It begins with a noun (التربة) and then gives information about it (رطبة).

If you wanted a past meaning, Arabic would use a verb such as كانت:

• كانت التربة رطبة = The soil was moist

Because التربة is a feminine noun, and adjectives in Arabic must agree with the noun they describe.

So:

• التربة = a feminine noun
• رطبة = feminine form of moist

Compare:

• تراب رطب = moist dust/soil-like material (masculine noun, masculine adjective)
• تربة رطبة = moist soil (feminine noun, feminine adjective)

The ـة at the end of رطبة is a common sign of the feminine form.

Because the first part of the sentence is not a verb clause; it is a nominal sentence:

• التربة = the topic / subject
• رطبة = the description / predicate

Then the phrase منذ أن سقى... adds the time meaning: since my friend watered...

So the structure is basically:

• The soil is moist
• since my friend watered the houseplant

Arabic often uses this kind of structure very naturally.

منذ أن means since when it introduces a clause.

So:

• منذ أن سقى صديقي النبات المنزلي = since my friend watered the houseplant

A useful distinction:

• منذ
  • noun/time expression
    
    • منذ يومين = since two days ago / for two days
• منذ أن
  • full clause
    
    • منذ أن وصل = since he arrived

Here, because a whole action follows (my friend watered...), أن is used to introduce that clause.

This verb is a weak verb. Its dictionary form is سقى (to water, to irrigate), and in the 3rd person masculine singular past tense it is also سقى:

• سقى = he watered

The final ى is called alif maqṣūra. Even though it looks a bit like ي, here it represents a final long ā sound.

So it is pronounced roughly saqā, not saqī.

Because صديقي means my friend.

Arabic adds possessive suffixes directly to nouns:

• صديق = a friend
• صديقي = my friend
• صديقك = your friend
• صديقه = his friend

So in this sentence:

• سقى صديقي... = my friend watered...

The doer of the action is صديقي (my friend), and the thing receiving the action is النبات المنزلي (the houseplant).

So:

• سقى = watered
• صديقي = my friend → subject/doer
• النبات المنزلي = the houseplant → object

This is a normal Arabic verb–subject–object order:

• سقى صديقي النبات المنزلي = My friend watered the houseplant

Because adjectives normally come after the noun in Arabic.

So:

• النبات = the plant
• المنزلي = domestic / home / household

Together:

• النبات المنزلي = the houseplant

This is the opposite of English, where adjectives usually come before the noun.

Compare:

• English: the houseplant
• Arabic: the plant the-household/domestic

Because Arabic adjectives must agree with the noun in definiteness as well as gender and number.

So if the noun is definite, the adjective must also be definite:

• نبات منزلي = an indoor plant / a houseplant
• النبات المنزلي = the indoor plant / the houseplant

In this sentence, the plant is definite, so both words take الـ.

Sometimes you may see منذ used without أن, but منذ أن is a very common and clear way to say since before a full clause in Modern Standard Arabic.

So for a learner, منذ أن is a very safe and useful pattern:

• منذ أن وصل
• منذ أن بدأت الدراسة
• منذ أن سقى صديقي النبات المنزلي

It is best to learn منذ أن + clause as a standard pattern.

In fully vocalized formal Arabic, it would be:

• التُّرْبَةُ رَطْبَةٌ مُنْذُ أَنْ سَقَى صَدِيقِي النَّبَاتَ المَنْزِلِيَّ

A simplified breakdown:

• التربةُ: nominative, because it is the topic/subject of the nominal sentence
• رطبةٌ: nominative, because it is the predicate
• النباتَ: accusative, because it is the direct object of سقى
• المنزليَّ: accusative too, because it describes النباتَ

In normal reading and speech, these endings are often not pronounced fully, especially outside very formal contexts.

Yes, literally it is something like the domestic/home plant, but the natural English meaning is the houseplant or the indoor plant.

This is very common in Arabic: a phrase may be more literal word-for-word, but you translate it with the natural English expression.

So:

• نبات منزلي = houseplant / indoor plant
• النبات المنزلي = the houseplant / the indoor plant

Yes. Arabic often allows some flexibility, though the exact emphasis may change.

For example, this sentence already has:

• التربة رطبة منذ أن سقى صديقي النبات المنزلي

A different arrangement might emphasize something else, but the given version is very natural and straightforward.

Inside the clause after منذ أن, the verb-first order is especially common:

• سقى صديقي النبات المنزلي

That is a standard and natural MSA structure.