The Lily Farm in Center, Texas has many shade structures over their daylilies that are for sale. There are different types of shade cloth, and you might want to ask them what percentage of sunlight is allowed in their shade cloth.

I have not found that sun negatively affects young seedlings. We transplanted all of ours into the daylily bed last September. Of course, they were started on our patio, where they did get sun part of the day. The newly sprouted ones were placed in full shade, and once they had two sets of leaves, we gradually moved them around until they were in full sun all day.

We tried making a shade structure similar to yours, but our mistake was that we didn't use any rebar. It eventually collapsed on us. You could also use some steel electrical conduit pipe that is large enough to hold the pvc arches.

Hope this helps...

Nancy