I declare this the Year of the Thistle.

This September, the country will have the opportunity to grasp it and set us off in an exciting new direction, so Scots gardeners should celebrate this by planting a thistle, a symbol of our nation.

The thistle genus, cirsium, has lots of members, but since many are on the prickly side, you could always choose a less aggressive ornamental one.

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Many different thistles grow wild here. Which one is our national emblem and why did we choose it?

According to legend, the Scottish thistle was first adopted after the Battle of Largs in 1263. While creeping up under cover of darkness on the unsuspecting Scots, one poor Viking soldier had given the game away by howling in agony after treading on a thistle.

It was supposed to have been a dwarf thistle, which doesn't grow wild north of Yorkshire, and this lovely tale dates back to 1829, six centuries after the event.

We're on firmer ground when we move forward to the reign of James III. In 1470, a thistle appeared on one of his coins, the groat.

The Stewarts started using the thistle whenever they could: James V had "thistillis of gold … upon … [his] bonnet".

Heraldry became all the rage in the 15th century, with kings and nobles madly searching around for symbols, but the Stewart thistle was a strange choice.

Plantsman Richard Mabey is probably right in saying: "No doubt the plant embodied the qualities the Stewarts [and by extension the Scots] saw as their own - tough and durable, proud and fearless, defiant against aggressors." Wha's like us, after all.

Onopordum acanthium, the cotton or Scottish thistle, closely resembles the plant used in heraldry. But nobody knows for certain that this was our thistle.

Until recently, this plant was very rare in Scotland and I can't believe the Stewarts would have chosen a rare specimen.

In the days before uniforms, the king's men were identified by the "badge" they wore. To avoid being run through by a friendly sword, there had to be lots of thistles around for the soldiers.

Nonetheless, Sir Walter Scott settled on this unlikely plant in 1822 by including onopordum in a pageant to celebrate George IV's trip up to his Scottish capital.

Far be it for me to question the eminent Sir Walter, but the Stewarts probably never set eye on the "Scottish" thistle; the thistle they knew was the spear thistle, Cirsium vulgare. We may have been backing the wrong flower for a couple of centuries.

Given all this uncertainty, feel free to celebrate 2014 by planting whatever thistle you fancy.

True thistles belong to the cirsium genus but domesticated versions are less aggressively prickly. C rivulare "Atropurpureum" is a good specimen, growing to about 1.2 metres. Deep crimson flowers top this fine plant. It sits well when planted in clumps in a border or in a wildflower meadow. Although it copes with dry, partial shade, it does best in a sunny spot with good moist soil.

Most garden thistles are only thistles in name and belong to different genera. You'll keep a straighter face when you refer to Silybum marianum as lady's milk thistle. As a biennial, it's not a gardener's first choice, but is a good tough beast. It forms a rosette of spiny, dark green leaves with prominent white veins and produces bonny crimson flowers in June and July.

Another group of thistle-like plants are echinops species, globe thistles. They're tall plants with globe-shaped blue-purple or white thistle flowers. E ritro varieties, such as "Globe Flower", usually grow to about one metre and flowers are different shades of blue. A slightly lower-growing variety, E sphaerocephalus "Arctic Glow", has white spherical flowers and grey leaves.

You could always plant these different blue and white echinops in the appropriate shape to commemorate 2014 with your very own thistle Saltire.