L’excès d’eau rend la racine pourrie.

This is because of elision in French.

• le excès becomes l’excès
• de eau becomes d’eau

French usually drops the vowel of le, la, or de before a word that starts with a vowel sound, and replaces it with an apostrophe.

So:

• l’excès = the excess
• d’eau = of water

After a noun like excès, French normally uses de to introduce what there is too much of.

So you get patterns like:

• un excès de sucre = an excess of sugar
• un manque de temps = a lack of time
• beaucoup d’eau = a lot of water

Here, excès already carries the idea of quantity, so French uses de, not de l’.

Yes, essentially.

• l’excès d’eau literally means the excess of water
• In natural English, that is often just too much water

In French, l’excès d’eau sounds a bit more formal or technical than trop d’eau, but both can express the same basic idea depending on context.

Rend comes from rendre, and one very common use of rendre is:

rendre + object + adjective

This means to make something/someone become a certain state.

So:

• L’excès d’eau rend la racine pourrie
  = Excess water makes the root rotten

Other examples:

• Cette nouvelle me rend triste = This news makes me sad
• Le soleil rend la pièce chaude = The sun makes the room warm

So rend here means makes or renders.

Rend is:

• present tense
• third-person singular
• from the verb rendre

It is third-person singular because the subject is l’excès d’eau, which is singular.

You can think of it as:

• l’excès d’eau rend = excess water makes

Not exactly.

In this sentence, pourrie is not just there to identify the root as already rotten. It shows the resulting state caused by rend.

So the structure is really:

• rend
  • la racine
    • pourrie
• makes
  • the root
    • rotten

This is similar to English sentences like:

• It painted the door red
• The news made him sad

So here the idea is makes the root rotten, not merely affects the rotten root.

Because pourrie agrees with la racine.

• racine is feminine singular
• so the adjective/complement must also be feminine singular

Forms of pourri are:

• pourri = masculine singular
• pourrie = feminine singular
• pourris = masculine plural
• pourries = feminine plural

Since the sentence has la racine, the correct form is pourrie.

It is originally the past participle of pourrir (to rot), but here it is being used like an adjective.

That is very common in French.

So in this sentence, pourrie describes the state of the root: rotten.

You can think of it as similar to English words like broken, closed, or tired, which can come from verbs but function as adjectives.

French often uses the definite article for general statements, where English might use a, the, or even no article depending on the wording.

So la racine can mean:

• the root in a general sense
• the root of a plant being discussed
• root tissue as a general category

French often sounds more natural than English with the definite article in this kind of statement.

It is understandable and grammatically possible, but many speakers might also say:

• L’excès d’eau fait pourrir la racine
• L’excès d’eau fait pourrir les racines

These versions use faire + infinitive (to make/cause to rot), which can sound more direct and natural in some contexts.

The difference is roughly:

• rendre + adjective focuses on the resulting state
• faire + infinitive focuses on causing the action/process

So rend la racine pourrie emphasizes that the root ends up rotten.