Questions & Answers about Vikendom često kupujem voće na tržnici.
Vikendom is the instrumental singular form of vikend (weekend), but it’s used adverbially to mean on weekends / at the weekend in general.
Croatian often uses bare case forms to express time, without a preposition. Other similar examples:
- zimi – in winter
- noću – at night
- ponedjeljkom – on Mondays
So you don’t say na vikendu for this meaning; vikendom alone already expresses on weekends in a habitual sense.
All can be translated with on/at the weekend, but there are nuances:
- vikendom – generally on weekends as a repeated, habitual action.
- Implies “whenever it’s the weekend, this is what I (tend to) do.”
- za vikend – at/over the weekend; can be habitual, but very often refers to a specific upcoming or past weekend:
- Što radiš za vikend? – What are you doing this weekend?
- svakog vikenda – every weekend, explicitly stressing regularity:
- Stronger than vikendom, leaves no doubt that it’s every single weekend.
In your sentence, vikendom fits because the action is described as a general habit.