Answer: I am not certain why you felt the sun was causing dried tips on your Nishiki. In my experience, as with other willows, Salix integra 'Hakura Nishiki'typically grows best in full sun. Drying leaf tips would usually be a sign of overly dry soil; willows, including this one, do best in an evenly moist to damp soil -- although some will toelrate average soil moisture levels once established. A new plant still in the establishment phase would be especially at risk for overly dry soil.
If your plant is now in at least six hours of sun, that is probably sufficient. Transplanting is stressful on a plant, and mid-summer transplanting is especially rough on them, and since you have already moved it once this summer I would not suggest moving it again unless it is planted in a shady area. If so, and you need to move it again, I would suggest waiting until the heat breaks at the end of August before you move it again. This will minimize the stress.
In the meantime, make sure to water it as needed to supplement rainfall and keep the soil generously moist. Using several inches of organic mulch will also help keep the soil more evenly moist. Watering deeply less often is better than a daily light sprinking. A few hours after you water, dig down with your finger to see how effective it was, sometimes it is surprising. Also use your finger to feel down into the soil to check and see if and when you need to water again.
Newly planted shrubs and trees should be watered as needed to supplement rain for the first entire growing season and up until the ground freezes in the fall. The second season, water during hot or dry spells and after that, water in extended hot or dry spells. Since this plant likes a more evenly moist soil, watering is especially important.
I know it is difficult to be patient, but with the planting, transplanting and now shade and possibly overly dry soil, your plant is most likely stressed and will be growing slowly.
Please do not be tempted to fertilize it at this point, a stressed plant simply needs time to root well and recover.
Once the plant is settled in its permanent location, next spring you could fertilize it with a complete granular fertilizer such as 10-10-10 according to label instructions and/or apply a layer of compost early next spring. Good luck with your willow!
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