Symbols

Leeks

It was said that St. David ate only leeks when he was fasting. Legend also tells us that King Cadwaladr of Gwynedd met the Saxons in battle on a field of leeks. The king ordered the wearing of leeks on his soldiers’ helmets during the battle so that they could be distinguished from the enemy. (From BedfordGazzette.com)

There is much more historical precedent for wearing a leek on St David's Day, as records detailing this go back to the 6th century; according to folklore, St David himself ordered Welsh soldiers to wear leeks into battle against the much-hated Saxons, and in the 14th century Welsh archers decked themselves out in green and white leek-themed uniforms. (From GrowWildUK.com)

Daffodil

The true St David’s Day daffodil is considered by some to be the Tenby daffodil (N. pseudonarcissus subspecies major, also known by the synonym N. obvallaris), which grows wild in South Wales. The wild daffodil is thought to have been a symbol of Wales since the 19th century. Its popularity may have come from a link with the Welsh for daffodil, ‘Cenhinen Bedr’, which means St Peter's Leek - and of course, the flower tends to be in bloom around early march, the time of St David’s Day. 

There is much more historical precedent for wearing a leek on St David's Day, as records detailing this go back to the 6th century; according to folklore, St David himself ordered Welsh soldiers to wear leeks into battle against the much-hated Saxons, and in the 14th century Welsh archers decked themselves out in green and white leek-themed uniforms. (From GrowWildUK.com)

Flag

The flag incorporates the dragon of Cadwaladr, King of Gwynedd, along with the Tudor colors of green and white. It was used by Henry VII at the Battle of Bosworth in 1485, after which it was carried in state to St Paul's Cathedral. The red dragon was then included as a supporter of the Tudor royal arms to signify their Welsh descent. It was officially recognized as the Welsh national flag in 1959. 

The United Kingdom would not recognize the flag's official status until 1959, but the red dragon had been associated with Wales for at least a thousand years. The green and white stripes of the flag were additions by the House of Tudor, the Welsh dynasty that held the English throne from 1485 to 1603. Green and white are also the colors of another national emblem of Wales, the leek. 

The red dragon is popularly believed to have been the battle standard of Arthur and other ancient Celtic/Romano-British leaders. (From Wikipedia)

National Anthem

The old land of my fathers is dear to me,

Land of bards and singers, famous men of renown;

Her brave warriors, very splendid patriots,

For freedom shed their blood.

Country, Country, I am faithful to my Country.

While the sea [is] a wall to the pure, most loved land,

O may the old language [sc. Welsh] endure.

Old mountainous Wales, paradise of the bard,

Every valley, every cliff, to my look is beautiful.

Through patriotic feeling, so charming is the murmur

Of her brooks, rivers, to me.

If the enemy oppresses my land under his foot,

The old language of the Welsh is as alive as ever.

The muse is not hindered by the hideous hand of treason,

Nor [is] the melodious harp of my country.

(From Wikipedia)