Bluebell Bulbs (scilla) are perfect for sowing under trees. They are blue bell flowers atop green strap like leaves. Bluebells are really easy to grow and they can naturalise under trees, forming a carpet of blue flowers during February.
Bluebells can be planted from bulbs during the Autumn months, September to November. When planting the Bluebell bulbs, dig a hole twice as big as the bulb itself.