Ah, yes, the cultivation of the watermelon. So it goes, Greek, as usual, being the vehicle of the secrets of philosophical interior peace.
But Η καλλιέργεια είναι νόμιμη was translated as "the crop is legal".
My dictionary also gives both "cultivation, farming" (= activity) and "crop" for καλλιέργεια.
Can the Greek word not mean both things?
I'm really sorry either I didn't see your comment or I just neglected to act on it but you are of course correct. "καλλιέργεια" can mean "crop". It's been added.
"the crop of watermelon" isn't accepted but it gives "The cultivation of watermelon" as the suggested answer.
Surely cultivation refers to the process of growing a crop, and harvesting refers to the bringing in of the crop after cultivation when it is ripe. I don't speak Greek but does the εργεια of καλλιέργεια not refer in some way to the working of the land, preparing the ground, planting seeds, hoeing, watering etc all needing work.
"καλλιέργεια" in the right context can be used both for "cultivation" and "crop".
E.g. γενετικά τροποποιημένες καλλιέργειες genetically modified crops.
συντήρηση των καλλιεργειών crop maintenance
Here's my go-to set of dictionaries. https://www.lexilogos.com/english/greek_dictionary.htm
I've checked every means I know to detect what the error could be that prevents this from being accepted and haven't been able to resolve it. Please send us a screenshot showing the exercise, what you wrote, and the response from Duolingo.