Q Will anything grow under large weeping willow?
A Apart from casting shade, the trailing stems of weeping willows swish around the soil surface, preventing anything from growing. If you carefully shorten them, without giving the plant a ‘fringe’, it will allow plants to grow underneath.
Willows famously suck out any soil moisture; a real problem in summer. So, the easiest plants to grow, are spring-flowering snowdrops, aconites, crocus, anemones and daffodils. If you can improve the soil, go for tough groundcover plants such as lamium, epimedium and periwinkle, watering while they get established.