Mense Maio hortus plenus florum fit, et Maius aviae semper gratissimus est.

Because Latin often uses the ablative of time when without a preposition.

So:

• mense = in the month
• Maio = of May / May agreeing with mense

Together, mense Maio means in the month of May or simply in May.

A native English speaker often expects a preposition like in, but Latin does not need one here.

They are two different cases of the same word.

• Maio is ablative singular, because it goes with mense in mense Maio
• Maius is nominative singular, because it is the subject of est

So:

• mense Maio = in the month of May
• Maius ... est = May is ...

This is a very common Latin pattern: the form changes depending on the word’s job in the sentence.

Originally it is an adjective, as in mensis Maius = the month of May. But Latin often leaves out mensis when the meaning is obvious.

So Maius by itself means May, with mensis understood.

That is why gratissimus is masculine too: it agrees with the understood masculine noun mensis.

The subject of fit is hortus.

• hortus = the garden
• fit = becomes
• plenus florum = full of flowers

Here plenus is a predicate adjective. It describes what the garden becomes.

So the structure is:

• hortus ... fit = the garden becomes ...
• plenus agrees with hortus
• florum depends on plenus

In other words: the garden becomes full of flowers.

Because plenus usually takes the genitive in Latin.

So:

• flores would mean flowers as a direct object or subject, depending on context
• florum means of flowers

Latin says plenus florum = full of flowers.

This is one of those places where English and Latin build the phrase differently.

Fit comes from fio, fieri and usually means becomes, comes to be, or is made.

So hortus plenus florum fit is more literally:

• the garden becomes full of flowers

In smoother English, someone might translate it as the garden is full of flowers in May, but the Latin verb itself suggests a change or coming-into-being.

Because gratus and gratissimus are used with the dative of the person pleased.

So:

• Maius aviae gratissimus est
• literally: May is most pleasing to grandmother

That is why aviae means to grandmother or for grandmother, not grandmother as the subject.

A very natural English translation would be: Grandmother likes May best or May is always grandmother’s favorite.

Gratissimus is the superlative of gratus.

• gratus = pleasing, welcome
• gratior = more pleasing
• gratissimus = most pleasing, very pleasing

So the sentence is not just saying that May is pleasing to grandmother, but that it is especially pleasing to her — probably her favorite month.

With semper, the sense is something like: May is always the most pleasing month to grandmother.

Because it agrees with Maius, the subject.

• Maius is masculine singular
• gratissimus must match it in gender, number, and case

This makes sense if you remember that Maius stands for mensis Maius, and mensis is masculine.

Latin word order is much more flexible than English word order because the endings show each word’s role.

This sentence puts important ideas first:

• Mense Maio sets the time right away
• hortus comes early as the topic of the first clause
• aviae is placed before semper gratissimus est to highlight the person affected

An English speaker may want a more fixed order like: In May the garden becomes full of flowers, and May is always most pleasing to grandmother.

But the Latin order is perfectly normal and often chosen for emphasis or style.