Hi, welcome to G o y, it all depends on how clayey your soil is, not much will grow in solid clay, but if you mix garden compost, well rotted manure, anything that contains humous in with the clay soil, they should grow quite well, with clay it's the drainage that's the problem, as there are usually plenty of nutrients in clay, because they don't wash out so easily, just break up the bottom of the planting hole with the above materials, add a layer of grit when planting, and backfill with the mixed clay compost, etc, and there should be no problem, Derek.

Drainage is likely to be the main issue. Crocosmia will grow just about anywhere and should be no problem; the alliums do not like a waterlogged soil.

They both do well on my heavy clay. I did mix in a good amount of grit when planting the alliums. So far so good.

Both do well in my heavy clay soil too and I didn't add any grit; just a handful of commercial compost.