If you're talking about Convulvulus cneorum, then a semi-shade position won't suit it, I'm afraid. I had two - the one in semi-shade didn't thrive and only produced a couple of flowers. :-((( The one in full sun is wonderful and loves it there. It flowers profusely.

All recommendations for this plant are for full sun - and my own exoperience backs that up.

Agree with Spritz, needs full sun, sheltered situation. Best planted in March.