Perennials in hibernation
Most perennials are completely hardy, so they don't need any help to overwinter. However, there are also varieties that want winter cover to survive the cold unscathed. These include, in particular, evergreen perennials.
Note: When buying your perennials, find out what to do with the plants in winter.
Time limit winter coverage
For perennials that need winter cover, you can use a layer of spruce twigs. Limit the time of the measure to the bare minimum, as the cover increases the susceptibility to pests and fungal attack in warm weather.
Dying of thirst is the most common cause of winter damage
It is interesting that the majority of winter damage to perennials is not caused by freezing, but by dying of thirst. Don't underestimate the power of the winter sun. Provide shade - with a suitable cover.
Also important: listen in good time to the (nitrogen-stressed) Fertilize on, at the latest in July.