Certified GKH Gardening Expert
Actually, clay soil will contain quite a bit of iron, already! Amending clay soils should be done with soft organic material, such as perlite, vermiculite, coco-coir, peat-moss, or other materials to break up the clay content. By far, the best way to amend the soil will be compost. Well composted organic material will break up the stickiness of the soil, while adding all of the nutrients that will be missing.