Comfrey prefers partial shade to full shade. While it can tolerate some sun, especially in cooler climates, it thrives best in a location that receives at least 4 hours of shade per day, particularly during the hottest part of the day.

Here's why:

* Shade protects the leaves: Comfrey leaves are large and can easily get scorched in direct sun, especially in hotter climates.

* Moist soil: Shade helps to keep the soil moist, which is essential for comfrey's growth.

* Reduced competition: Comfrey is a vigorous grower, but it can be outcompeted by other plants in full sun. Shade can help to give comfrey an edge in its competition for resources.

In summary: While comfrey can tolerate some sun, it's best to plant it in a location that gets at least 4 hours of shade per day. This will help to keep its leaves healthy and the soil moist, promoting optimal growth.