Is sycamore soil toxic?

I planted spring bulbs (snowdrops and bluebell H. nonscripta) under a sycamore tree and nothing has come up. I cleared and raked the area well before planting, cut away the lowest branches, so there’s plenty of light and rain getting to the soil, but still not flowers. Just wondering if the sycamore itself might be inhibiting growth. I know it happens with beech.