To propagate a foxtail lily (Eremurus), the most common method is by dividing established clumps in the fall after the foliage dies back, ensuring each division has healthy roots and a crown, and then replanting them separately; you can also try propagating from seed, but this can be more challenging and may not produce identical plants to the parent, requiring a cold stratification period for germination. 

Key points about propagating foxtail lilies:

Division:

Best time: Late fall after the foliage dies down. 

Process: Carefully dig up the plant, gently separate the smaller offsets with roots attached, and replant them spaced apart. 

Important consideration: Be careful not to damage the brittle roots while dividing. 

Seed propagation

Harvesting seeds: Collect seeds in autumn after flowering. 

Germination: Sow seeds in a tray with compost, and expose them to a cold stratification period (like in a cold frame) to promote germination. 

Challenges: Seed propagation can be unpredictable and may take a long time to establish.