La maceta tiene buen drenaje.

Because maceta is a feminine singular noun, so it takes the feminine singular article la.

• la maceta = the plant pot / flowerpot
• una maceta = a plant pot / flowerpot

The sentence uses la because it is talking about the pot, not just any pot.

Maceta usually means plant pot, flowerpot, or pot for a plant.

In Spain, this is the normal everyday word for a pot that holds a plant. It refers to the container, not the plant itself.

Tiene is the third person singular form of the verb tener (to have).

Here, the subject is la maceta, which is singular, so you need:

• la maceta tiene = the pot has

Even though a pot is not a person, Spanish uses tener just like English uses have for things:

• La casa tiene jardín. = The house has a garden.
• El coche tiene cuatro puertas. = The car has four doors.

Because bueno becomes buen when it comes before a singular masculine noun.

Since drenaje is masculine singular, you get:

• buen drenaje ✔
• bueno drenaje ✘

Compare:

• un buen libro
• buen tiempo
• un buen resultado

But after the noun, it stays bueno:

• El drenaje es bueno.

Because drenaje is a masculine noun in Spanish.

You can tell from how it combines with other words:

• el drenaje
• un drenaje
• buen drenaje

A useful pattern is that many nouns ending in -aje are masculine:

• el garaje
• el paisaje
• el viaje
• el drenaje

Yes, absolutely.

Both are natural, but there is a small difference in feel:

• La maceta tiene buen drenaje. = more general; it has good drainage
• La maceta tiene un buen drenaje. = also correct; slightly more concrete or countable in feel

In many contexts, Spanish often leaves out un with this kind of expression, especially when speaking generally about a quality.

Because Spanish often uses a noun without an article when talking about a quality or characteristic in a general way.

So:

• tiene buen drenaje = it has good drainage

This is similar to other common patterns:

• Tiene buena memoria.
• Tiene mal carácter.
• Tiene mucha paciencia.

Adding un is possible, but without it the sentence sounds very natural and general.

Yes, it is completely normal.

The structure is:

• La maceta = subject
• tiene = verb
• buen drenaje = direct object

So the sentence follows the usual Spanish order:

subject + verb + object

Also, in Spanish, adjectives usually come after the noun, but some common adjectives like bueno can go before the noun, and when they do, bueno shortens to buen.

A rough pronunciation guide is:

lah mah-SEH-tah TYEH-neh bwehn dreh-NAH-heh

A few details for Spain:

• c before e in maceta is pronounced like th in Castilian Spain: ma-THE-ta
• j in drenaje is a strong throaty sound: dre-NA-he
• ie in tiene forms one syllable sound: TYE-ne

A more Spain-based pronunciation would be roughly:

la ma-THE-ta TYE-ne bwen dre-NA-je
(with the Spanish j sound, not an English j)

Yes. Drenaje is a normal and natural word, especially in gardening, soil, and plant-care contexts.

For example:

• Esta tierra tiene buen drenaje.
• La maceta necesita mejor drenaje.
• El drenaje es importante para las raíces.

So La maceta tiene buen drenaje sounds perfectly natural when talking about plant pots.

Yes. A few natural alternatives are:

• La maceta drena bien. = The pot drains well.
• La maceta tiene un buen sistema de drenaje. = The pot has a good drainage system.
• El drenaje de la maceta es bueno. = The pot’s drainage is good.

Your original sentence is one of the most straightforward and natural ways to express the idea.