Too heavy soil? I grow Lindera obtusiloba in partial shade in woodland soil, moist, rich in humus and fluffy. It likes it there. Is your soil overly wet after rain?

Lindera do best in moist, fertile acidic soils that drain well. Maybe you need to fertilize or water more. Or both. Are they mulched? This typically produces a visible improvement in plant response.

Thanks. I'll try the mulch. The drainage should be good, but they might be a little under watered during summer and dry days. Never have fertilized. Thanks!!