Mi abuela dice que el pelador corta mejor que el cuchillo cuando la patata está húmeda.

In modern standard Spanish, possessives like mi, tu, su, nuestro normally replace the article, so you say:

• mi abuela
• tu hermano
• su casa

Not la mi abuela.

Very occasionally, forms like la mi casa appear in older, literary, or regional language, but they are not normal everyday Spanish.

After verbs of saying, thinking, knowing, etc., Spanish very often uses que to introduce the next clause:

• Dice que... = She says that...
• Pienso que... = I think that...
• Sé que... = I know that...

So Mi abuela dice que... is the normal way to say My grandmother says that...

English often drops that, but Spanish usually keeps que.

Spanish usually uses the definite article more often than English, especially with nouns used in a general or known sense.

Here, el pelador and el cuchillo refer to the tools as categories or as the specific tools being discussed:

• el pelador = the peeler
• el cuchillo = the knife

English might sometimes omit an article in more general statements, but Spanish normally keeps it with singular count nouns.

Here pelador means peeler, the kitchen tool used to peel vegetables.

It comes from the verb pelar = to peel.

So:

• pelar = to peel
• pelador = peeler

Depending on context, pelador can also mean someone who peels, but in this sentence it clearly means the utensil.

Mejor is the irregular comparative form of bien and also works in expressions like this to mean better.

So:

• bien = well
• mejor = better

You say:

• corta bien = it cuts well
• corta mejor = it cuts better

Not:

• más mejor ❌

And más bien usually means something like rather or more accurately, so it would not fit here.

To compare two things in Spanish, you often use:

• más ... que = more ... than
• mejor que = better than
• peor que = worse than

So:

• el pelador corta mejor que el cuchillo

literally means the peeler cuts better than the knife.

Because mejor already contains the comparative idea, you do not add más.

Corta is perfectly natural because a peeler does cut the surface of the potato.

But depending on what exactly you want to emphasize, pela could also work in another sentence:

• El pelador pela mejor que el cuchillo = The peeler peels better than the knife.

Your sentence uses corta mejor, which focuses on cutting performance. That is grammatically fine and understandable.

Spanish often uses the definite article with nouns when talking about something specific or something understood in context.

Here la patata probably means the potato being peeled, not potatoes in general as a broad category.

So:

• cuando la patata está húmeda = when the potato is damp

If you were making a more general statement about potatoes as a class, Spanish might still use the article depending on structure, but in this sentence the article sounds very natural.

In Spain, patata is the normal everyday word.

In many Latin American countries, papa is more common.

So for Spanish from Spain:

• patata = the usual choice

Both words are understood widely, but patata fits the Spain variety you asked about.

Spanish uses estar for temporary states or conditions, and ser for more permanent characteristics or identity.

Here the potato is temporarily damp, so Spanish uses estar:

• la patata está húmeda = the potato is damp

If you said es húmeda, it would sound more like it is a damp/moist kind of potato by nature, which is not the intended meaning.

They are similar, but not identical.

• húmeda = damp, moist
• mojada = wet

Húmeda often suggests a lighter amount of moisture. Mojada usually sounds stronger, as if it has actually gotten wet.

So in this sentence, húmeda suggests the potato is a bit moist, which may affect how the tools work.

Spanish often uses the present tense for general truths, habits, and repeated observations.

This sentence sounds like your grandmother’s general opinion or experience:

• Mi abuela dice... = My grandmother says...
• el pelador corta mejor... = the peeler cuts better...
• cuando la patata está húmeda = when the potato is damp...

It is not just about one single moment. It sounds like a regular claim or rule of thumb.

Yes. Spanish word order is flexible, especially with time clauses like cuando...

For example, you could also say:

• Mi abuela dice que cuando la patata está húmeda, el pelador corta mejor que el cuchillo.

This means the same thing. The original version places the main comparison first and adds the condition after it. The alternative puts the condition earlier.

Both are natural.

A few useful points:

• The h is silent.
• The stress is marked by the accent: hú-
• So it sounds roughly like OO-meh-dha in much of Spain, with the Spanish d sound being softer than English d between vowels.

Very roughly:

• húmeda → Ú-me-da

The written accent mark is important because it shows the stressed syllable.

Because the sentence is talking about a usual, real situation, not a future or hypothetical one.

Compare:

• cuando la patata está húmeda = when the potato is damp
  
  • general or real condition
• cuando la patata esté húmeda = when the potato is damp / once the potato is damp
  
  • more future-oriented or specific to a later event

In your sentence, the speaker is expressing a general observation, so the present indicative está is the natural choice.