The leaf habit of grandiflora varies greatly in size and shape. I've seen trees with nearly round leaves, some with narrow elogated leaves, some with large leaves up to 10 inches in length and other with small leaves that average less than four inches. I've found plenty of leaves that are the size of my thumb.
Magnolia virginiana is also referred to as sweet bay and although the leaves are less durable, I see no reason these cannot be used.
There is actually a magnolia referred to as the Umbrella Magnolia (Magnolia tripetala) and it is found further north than the southern magnolia. I believe it is deciduous and the leaves break down fairly quickly, but again, they can certainly be used to make tadpole tea or viv leaf litter.
Magnolia virginiana is also referred to as sweet bay and although the leaves are less durable, I see no reason these cannot be used.
There is actually a magnolia referred to as the Umbrella Magnolia (Magnolia tripetala) and it is found further north than the southern magnolia. I believe it is deciduous and the leaves break down fairly quickly, but again, they can certainly be used to make tadpole tea or viv leaf litter.