Within the Celtic forest, the Ash is inferior only to the Oak. It readily springs from seed and when conditions are favourable, grows with great rapidity. Its roots have the unusual tendency to grow horizontally producing many fibres close to the surface that check the growth of almost all other vegetation. The roots dislike the presence of stagnant water, but thrive when close to the gravely bed of a running stream, often outstripping the growth of all other surrounding trees. Young plants are easily distinguished from other varieties in winter and early spring by their ash-coloured bark and black buds. In summer the tree is easily identified by its leaves composed of five pairs of leaflets with a single one on the end. In the autumn it is one of the first to shed its foliage.

As a timber-tree the ash has always been highly valued for its quickness of growth and the toughness and elasticity of its wood. In its younger stages (when it is known as ground Ash) it provides timber for walking-sticks, fencing, hoops and spear shafts. Its inner bark was used to write on before the invention of paper. The mature wood has long been used for making ploughs, wheel-rings, oars, blocks for pulleys, furniture and tool handles. It is also a most excellent fire wood burning even when green and producing the minimum of smoke. Medicinally, it has been used as a mild laxative and diuretic, to regulate the bowels, expel intestinal parasites, reduce fevers and treat kidney and urinary disorders.

In the countryside villages of certain parts of Britain, healing ceremonies were often performed utilising the ash. In his "History of Selborne", Gilbert White says: "In a farmyard in the middle of this village stands at this day a row of pollard-ashes, which, by the seams and long cicatrices down their sides, manifestly show that in former times they have been cleft asunder. These trees, when young and flexible, were severed and held open by wedges, while diseased children, stripped naked, were pushed through the apertures, under the persuasion that by such a process the poor babes would be cured of their infirmity. As soon as the operation was over, the tree in the suffering part was plastered with loam, and carefully swathed up. If the parts coalesced and soldered together, as usually fell out, where the feat was performed with any adroitness at all, the party was cured; but where the cleft continued to gape, the operation, it was supposed, would prove ineffectual. We have several persons in this village, who in their childhood were supposed to be healed by this ceremony."

Another more bizarre healing ritual involved boring a hole in an Ash and fastening within in a shrew-mouse. A few strokes with a branch of this tree provided a remedy for cramp and lameness in cattle, thought to be caused by this small animal. Such a tree was named "shrew-ash". Gilbert White wrote of one such tree that stood in the village of Selborne in the mid-eighteen hundreds. "At the south corner of the Plestor, or area near the church, there stood, about twenty years ago, a very old, grotesque, hollow pollard-ash, which for ages had been looked on with no small veneration as a shrew-ash. Now a shrew-ash is an Ash whose twigs or branches, when gently applied to the limbs of cattle, will immediately relieve the pains which a beast suffers from the running of the shrew-mouse over the part affected; for it is supposed that a shrew-mouse is of so baleful and deleterious a nature, that wherever it creeps over a beast, be it horse, cow, or sheep, the suffering animal is afflicted with cruel anguish, and threatened with the loss of the use of the limb. Against this accident, to which they were continually liable, our provident forefathers always kept a shrew-ash at hand, which, when once medicated, would maintain its virtues for ever. A shrew-ash is made thus:- Into the body of the tree a deep hole was bored with an auger, and a poor devoted shrew-mouse was thrust in alive, and plugged in, no doubt with several incantations long since forgotten."