Learn Finnish: Pellot ovat täällä vihreitä.

In Finnish, when you say that plural things are a certain way, the subject is in the nominative plural (the T-plural) but the describing adjective is almost always in the partitive plural. This is why we use vihreitä instead of vihreät.

The dictionary form for field is pelto. Why does it become pellot here?

Adding the plural -t ending closes the syllable, which triggers consonant gradation. The strong lt combination softens to the weak ll, giving us pellot.

Since we are learning about consonant gradation in the partitive plural, what would 'fields' be in that form?

The partitive plural of pelto is peltoja. Notice that the partitive plural ending -ja starts with a consonant but ends with a vowel, leaving the syllable open. Because the syllable remains open, it uses the strong grade lt instead of the weak ll seen in pellot.

How do we form the partitive plural vihreitä from the basic form vihreä?