May. Growers will ship the bulbs to you in September. Hillsides and raised beds are best. Spade at least twelve inches deep. Improve your clay with well-rotted compost, soil amendment, or planting mix and raise the bed. Slightly acidic soil is best, so you might add soil sulfur if you have alkaline soil.
Plant bulbs deeper in sandy soil than in clay.
High-nitrogen fertilizer should be avoided. Water immediately after planting and keep them moist until the rains come. The bulbs make their next year's bloom after flowering. Mulch the bed. If you water, or grow other things there, then you must dig them.