Tedd a mentát félárnyékba, nehogy elhervadjon.

Tedd is the 2nd person singular imperative, definite conjugation of tesz (to put / to place / to do in other contexts).

Here, the verb has a definite object: a mentát = the mint. Because Hungarian distinguishes between indefinite and definite object conjugation, you use the definite imperative form:

• tégy / tegyél = imperative without a definite object, or in more general use
• tedd = imperative used with a definite object

So:

• Tegyél mentát félárnyékba = Put some mint in partial shade
• Tedd a mentát félárnyékba = Put the mint in partial shade

In this sentence, tedd is exactly the expected form.

Because mentát is in the accusative case, which marks the direct object.

The direct object of tedd is a mentát (the mint), so Hungarian adds the accusative ending -t.

With many nouns ending in -a or -e, that final vowel often lengthens before certain endings:

• menta → mentát
• körte → körtét

So the change is:

• base noun: menta
• accusative: mentát

This is very common in Hungarian.

Félárnyék literally means something like half-shade:

• fél = half
• árnyék = shade

As a gardening term, it means partial shade or semi-shade.

The ending -ba / -be means into or to a place inside/into a state/location. Here it marks movement toward a location:

• félárnyékban = in partial shade
• félárnyékba = into / to partial shade

Because the verb tedd involves moving something somewhere, Hungarian uses -ba, not -ban.

Compare:

• A menta félárnyékban van. = The mint is in partial shade.
• Tedd a mentát félárnyékba. = Put the mint in partial shade.

Hungarian often leaves out the article when the destination is meant in a general, non-specific sense.

So félárnyékba here means roughly into partial shade as a condition or type of placement, not necessarily into that specific partially shaded spot.

That is why Tedd a mentát félárnyékba sounds natural.

If you were talking about a particular spot already known in the conversation, you might also hear:

• Tedd a mentát a félárnyékba.

That version points more toward the partial-shade area as a specific place.

So the version without the article is more general and very natural in advice or instructions.

Nehogy introduces a clause about avoiding an unwanted result. In English, it can often be translated as:

• so that ... doesn’t
• for fear that
• lest

So:

• nehogy elhervadjon = so that it doesn’t wilt / lest it wilt

It often has a slightly cautionary feeling, as if the speaker is warning against a bad outcome.

In everyday Hungarian, nehogy is very common in this kind of sentence:

• Vedd be a kabátod, nehogy megfázz. = Put on your coat so you don’t catch cold.

Because after nehogy, Hungarian normally uses the subjunctive / imperative-type form of the verb.

Elhervadjon is the 3rd person singular subjunctive form of elhervad.

Breakdown:

• elhervad = it wilts / it will wilt
• elhervadjon = that it wilt / that it should wilt in a subordinate clause

After nehogy, this is the expected grammar:

• nehogy elhervadjon
• not normally nehogy elhervad

This is one of the common places where English learners notice that Hungarian uses a special verb form after conjunctions expressing purpose, desire, fear, prevention, and so on.

The base verb is hervad = to wilt.

With the verbal prefix el-, it becomes elhervad, which often suggests a more complete change of state:

• hervad = is wilting / wilts
• elhervad = wilts away / becomes wilted

The prefix el- is very common in Hungarian and often gives a sense of:

• completion,
• change into a new state,
• or movement away.

So here elhervadjon is not just start wilting, but more like end up wilted.

Not completely. Hungarian word order is fairly flexible, and changing it often changes focus or emphasis, not the basic meaning.

The given sentence is a very natural, neutral way to say it:

• Tedd a mentát félárnyékba, nehogy elhervadjon.

But other orders are possible, for example:

• A mentát tedd félárnyékba, nehogy elhervadjon.
  This puts a bit more focus on the mint.

• Félárnyékba tedd a mentát, nehogy elhervadjon.
  This emphasizes where to put it.

The clause with nehogy elhervadjon naturally comes after the main instruction, because it gives the reason or precaution.

The subject of elhervadjon is understood to be the mint: a menta.

Even though menta is a plant name and can refer to mint in a general sense, here it is treated as a singular noun, so the verb is singular too:

• a menta ... elhervadjon = the mint ... wilt

Hungarian often leaves subjects unspoken when they are clear from context. In this sentence, the plant just mentioned is obviously the thing that might wilt, so there is no need to repeat it.