La radikoj putras kaj la folioj velkas en malseka substrato.

Because -o is the noun ending in Esperanto, and -j marks the plural.

So:

• radiko = a root
• radikoj = roots
• folio = a leaf
• folioj = leaves

Together, -oj means plural noun.

Esperanto often repeats la when two separate noun phrases are being mentioned.

So:

• la radikoj = the roots
• la folioj = the leaves

This is very natural and clear in Esperanto. English can sometimes omit the second the, but Esperanto commonly keeps it.

Both are present-tense verbs.

In Esperanto:

• -as = present tense

So:

• putras = rot / are rotting
• velkas = wilt / are wilting

A key point for English speakers: Esperanto verbs do not change according to person or number.

So the same form works for:

• mi putras
• vi putras
• la radikoj putras

Only the tense matters, not the subject.

Because Esperanto often uses a single verb where English uses be + adjective/participle or a progressive form.

Here:

• putri = to rot
• velki = to wilt

So:

• la radikoj putras = the roots are rotting
• la folioj velkas = the leaves are wilting

You do not need a separate verb like estas here.

This is a useful distinction:

• putras / velkas describe a process or change happening
• estas putraj / estas velkaj describe a state or condition

So:

• la radikoj putras = the roots are rotting
• la radikoj estas putraj = the roots are rotten

And:

• la folioj velkas = the leaves are wilting
• la folioj estas velkaj = the leaves are wilted

In your sentence, the verbs suggest something is actively happening.

Because malseka substrato comes after en, and here en shows location, not direction.

• en malseka substrato = in a wet substrate

The accusative -n is not used because nothing is moving into the substrate. It is just the place or condition in which this happens.

Compare:

• en malseka substrato = in a wet substrate
• en malsekan substraton = into a wet substrate

That second version would suggest movement into it.

Because -a is the adjective ending in Esperanto.

• malseka = wet
• substrato = substrate / growing medium

Adjectives match nouns in number and case when necessary. Here substrato is singular and has no accusative -n, so the adjective is simply malseka.

If the noun changed, the adjective would change too:

• malsekaj substratoj = wet substrates
• malsekan substraton = a wet substrate (object / direction)

It is built from smaller parts:

• seka = dry
• mal- = the opposite

So:

• malseka = wet

This is a very common Esperanto pattern. The prefix mal- creates an opposite meaning.

Examples:

• bona = good → malbona = bad
• varma = warm → malvarma = cold
• seka = dry → malseka = wet

Yes. Substrato is a normal Esperanto word, especially in technical, botanical, or gardening contexts.

It means something like:

• substrate
• growing medium
• material in which a plant grows

It is a more specialized word than grundo (soil, ground). In plant care, substrato can refer to potting mix, bark mix, moss, and other media, not just ordinary soil.

Usually yes, or at least to the overall situation.

The sentence structure is:

• La radikoj putras
• kaj la folioj velkas
• en malseka substrato

Most readers will understand that the wet substrate is the condition connected with the whole statement: in a wet substrate, the roots rot and the leaves wilt.

If you wanted to make the connection even clearer, Esperanto could also restructure the sentence, but the original is natural.

Because they are the subjects of the verbs, not direct objects.

• la radikoj putras → the roots are rotting
• la folioj velkas → the leaves are wilting

In Esperanto, the accusative -n is mainly used for direct objects and for certain directional meanings.

Since radikoj and folioj are the things doing or undergoing the action as subjects of the clause, they stay without -n.

Yes, in sentences like this, kaj simply means and.

It connects:

• words
• phrases
• clauses

Here it joins two clauses:

• La radikoj putras
• la folioj velkas

So the whole middle part is simply the roots rot and the leaves wilt.

A learner often asks this because the ending -oj can look unusual.

Very roughly:

• radikoj ≈ rah-dee-KOY
• folioj ≈ foh-LEE-oy

A few helpful points:

• j sounds like English y
• oj sounds roughly like oy
• stress is always on the second-to-last syllable

So:

• ra-DI-koj
• fo-LI-oj
• put-RAS
• VEL-kas
• mal-SE-ka sub-STRA-to

The Esperanto sentence literally uses en = in, not because of.

So the direct meaning is about the condition or environment:

• in a wet substrate

However, in real context, English might sometimes express the idea more naturally as a cause:

• The roots rot and the leaves wilt in wet substrate
• or because of wet substrate

But grammatically, Esperanto here says en, meaning in or under the condition of being in wet substrate, not explicitly pro (because of).