Learn Turkish: Bahçıvan çimleri sabahtan beri suluyor. - The gardener has been watering the grass since morning.

The verb root here is sula- (to water). Because it ends in a vowel, you apply the causative suffix -t to make the root sulat- (to have watered). The new verb form would be sulatıyor.

The English translation says 'has been watering'. Why is the present continuous tense (suluyor) used instead of a past tense?

In Turkish, when an action started in the past and is still continuing right now, you use the present continuous tense (-ıyor). The English 'has been doing' concept is expressed simply by combining this present tense with a time expression like sabahtan beri (since morning).

Why does sabah (morning) take the -tan ending before beri?

The postposition beri (since) always requires the preceding noun to take the ablative case (-dan/-den or -tan/-ten). Because sabah ends in a voiceless consonant (h), the suffix hardens to -tan.

In English, 'grass' is uncountable and singular. Why is çimleri plural here?

While 'grass' is uncountable in English, Turkish treats çim as a countable noun. When talking about a lawn or a yard covered in grass, Turkish speakers naturally use the plural çimler. The final -i is the accusative case suffix, marking it as the specific direct object of the verb.