Qingxin is a plant that is used to ascend certain characters in Genshin Impact. You will need it to ascend Xiao, Ganyu, and Chungyun. It can be exclusively found in the Liyue region, and only at the top of cliffs.
To get your hands on this plant, you will need to do a lot of climbing, as they only grow at the top of high cliffs. Not on the cliff face itself, but on grassy patches at the top of the cliffs. They do tend to grow in clusters or two to three plants quite close together, however.
Huaguang Stone Forest
The Stone Forest is a pretty easy to spot to farm them in, as they will grow in clusters near the teleport points, and the Statue of the Seven. It is easy to grab a quick dozen Qingxin plants here, but they will take two to three days to respawn afterward.
When looking for resources like this, you should have Qiqi in your party, if you are lucky enough to have her. She will mark these rare Liyue resources on your minimap, making them easier to find.
If you are stuck for Qingxin and cannot find any on the map, you can visit Babu Pharmacy in Liyue. Here, you can buy an assortment of plants, including Qingxin. You can buy up to 10 plants for 600 Mora each, and the stock will refresh every three days.