I'm not 100% certain where you are, but I vaguely recall its Europe somewhere - if so, no, you shouldn't have to water the ground at this time of year, unless you live somewhere like southern Italy. Pots, on the other hand, may want watering if its been very dry and relatively mild where you are - I'm in the UK and I did have to water balcony pots last week (south facing in London) and the small ones look like they need doing again now.
If you're uncertain about watering the ground, then take a trowel or a hand fork and turn over the top few inches - if its like dust, then it needs watering, but otherwise, it should be fine. Permanent plantings usually have good roots and the soil at this time of year should be pretty damp, and ground water levels restored, so watering should not be necessary, although it does depend on exactly where you are.
To address your last sentence, no, there isn't a way of telling when to start watering by any standard measurement. Last year, here, we had a warm winter followed by an early spring, and I was watering the ground for new (planted less than a year) plantings by the start of April. This year, it's been a little colder over winter, and temperatures are still currently relatively low, so no watering of the ground has been necessary. In other words, it depends entirely on what the weather's doing whether you need to water or not; generally speaking, if, say, March in Northern Europe is unseasonably hot (18-22degC), fairly windy and rain free, you may need to water small or newish plants by April. Larger shrubs and most perennials, if they've been planted for more than two years, will be fine and shouldn't need watering even in those conditions. It's now even harder to generalize about scheduling things like watering in the garden because of obvious changes in climate almost everywhere.