When you ask about yarrow sun or shade, the answer is clear. Yarrow is a full sun plant that needs six to eight hours of direct light every day. You can grow it in partial shade, but you will get far fewer blooms and weaker stems. Give your yarrow the brightest spot in your yard for the best results.
I tested this myself two summers ago by planting yarrow in two spots in my garden. One group went into a south-facing bed with full sun all day. The other group sat behind a tree that blocked light for half the afternoon. By midsummer, the full-sun yarrow stood tall with thick stems and dozens of flower heads. The shaded yarrow flopped over and made about half as many blooms. That one test sold me on full sun for good.
Your yarrow sunlight requirements tie back to how the plant evolved in the wild. Yarrow grew up as an early species in open meadows and bare ground after fires. It counts on strong, direct light to build thick stems that hold flower heads upright. When you put it in shade, the stems stretch thin trying to reach more light. That is why shaded yarrow tends to fall over and look messy in your garden.
USDA data shows yarrow growing from sea level all the way up to above 11,000 feet in open spots. It thrives across a huge range of climates, but the one thing every site has in common is plenty of sun. NC State Extension lists partial shade as something yarrow can handle, but they rate full sun as the best choice for you.
The broader yarrow growing conditions go beyond just light. Yarrow loves heat and drought and does fine in poor soil. It handles humidity too, though wet roots in shade can lead to mildew on your plants. Good drainage matters more than soil quality, and dry conditions won't bother yarrow at all once you get it going.
Here is what you should do when you plant your yarrow. Pick the sunniest bed you have and stay away from tree canopies or north-facing walls that block light. If your garden only gets four to six hours of sun, you can still grow yarrow but expect about 50% fewer flowers. South-facing and west-facing spots give you the strongest light in most yards.
I now keep all my yarrow in one long row along my south fence where nothing blocks the sky. Every plant gets full sun from morning to evening, and the bloom show is much better than what I got from my old mixed-light beds. You will notice the same boost in your own garden once you move yarrow to your brightest spot. Trust me, this single change makes all the gap between sad, floppy yarrow and a thick wall of flowers.
Read the full article: Yarrow Plant: A Complete Growing Guide
