Раз уж мы всё равно купили удобрение для фикуса, давай возьмём ещё одно и для орхидеи.

Раз уж is a conversational expression meaning something like:

• since
• seeing that
• as long as
• given that

In this sentence, it introduces the idea: since we’ve already bought fertilizer for the ficus...

It often adds a nuance of “well, since that’s already the case...” or “given that we’ve gone this far...”

So:

• Раз уж мы купили... = Since we bought...
• Раз уж ты здесь... = Since you’re here...

It is fairly common in spoken Russian.

Yes, всё равно often means anyway, all the same, or regardless.

Here it gives the sense of:

• since we bought it anyway
• since we were buying it regardless
• since we ended up buying it in any case

So Раз уж мы всё равно купили... means something like:

Since we bought it anyway / since we already bought it regardless...

This makes the suggestion sound natural: if we were already buying one fertilizer, we might as well get another.

Давай + first-person plural future/perfective is a very common way to say let’s ... in Russian.

So:

• давай возьмём = let’s take / let’s get

Here:

• давай = literally come on / let’s
• возьмём = we will take (from взять)

Together they form a suggestion:

давай возьмём ещё одно = let’s get one more

This is one of the most useful everyday patterns in Russian.

Russian often expresses let’s do X with:

• давай / давайте + 1st person plural form

So instead of a special English-style let’s, Russian uses:

• давай пойдём = let’s go
• давай посмотрим = let’s see
• давай возьмём = let’s take/get

The form возьмём is the 1st person plural future of the perfective verb взять. With давай, it becomes a suggestion.

Because одно agrees with an omitted noun: удобрение.

• удобрение = fertilizer
• it is neuter
• so one must also be neuter: одно

So:

• ещё одно (удобрение) = one more (fertilizer)

Compare:

• ещё один for masculine nouns
• ещё одна for feminine nouns
• ещё одно for neuter nouns

Examples:

• ещё один цветок = one more flower
• ещё одна орхидея = one more orchid
• ещё одно удобрение = one more fertilizer

Because Russian often omits a noun when it is obvious from context.

Here, удобрение has already been mentioned:

• купили удобрение для фикуса
• then возьмём ещё одно

So ещё одно means one more fertilizer without repeating удобрение.

English does this too:

• We bought one already; let’s get another.

Russian simply matches the gender of the omitted noun, which is why одно is enough.

Because after для (for), Russian normally uses the genitive case.

So:

• для фикуса = for the ficus
• для орхидеи = for the orchid

Base forms:

• фикус → фикуса
• орхидея → орхидеи

This is a very important pattern:

• для дома = for the house
• для брата = for the brother
• для машины = for the car

So in this sentence, both plant names are in the genitive because of для.

Here и means also / too, not just and in the basic sense.

So:

• ещё одно и для орхидеи = one more for the orchid too

This is a natural Russian way to add another item of the same kind.

The noun удобрение is understood again:

• возьмём ещё одно (удобрение) и для орхидеи

You could also say something with тоже, but и для орхидеи is very natural and compact.

Ещё here means more / another.

So:

• ещё одно = one more / another one

This is one of the common meanings of ещё. Depending on context, ещё can also mean:

• still
• yet
• else
• more

But in this sentence, the meaning is clearly another.

Because the subject is мы (we).

Russian past tense agrees in gender/number, not person:

• я купил / купила
• ты купил / купила
• он купил
• она купила
• мы купили
• они купили

So мы купили simply means we bought.

The word order is quite natural and conversational.

A rough structure is:

• Раз уж = since / seeing that
• мы всё равно купили удобрение для фикуса = we bought fertilizer for the ficus anyway
• давай возьмём ещё одно и для орхидеи = let’s get another one for the orchid too

Russian word order is flexible, but this order sounds smooth because it moves from:

1. the reason/background
2. to the suggestion

Also, placing всё равно before купили emphasizes the idea of anyway / in any case.

Yes, in Russian удобрение can be used as a countable item when you mean:

• a package
• a product
• a type/brand of fertilizer

So ещё одно is perfectly natural in a shopping context:

• one fertilizer for the ficus
• another fertilizer for the orchid

English often uses some fertilizer, but in stores we can also say things like a fertilizer for orchids or another one. Russian does this very naturally with удобрение.