I figured the best way to get a lemongrass plant started is to propagate from an existing plant. However, since none of our neighbours had one, the next best option was to try to get store bought lemongrass stalks to root.
First stop was a visit to our local Thai supermarket to pick up some very fresh lemongrass. Any of the big supermarket ones (Tesco, Waitrose etc.) should work too. When choosing lemongrass for propagation, make sure that the base of each stalk is still in tact and not rotten or mouldy. Also avoid any that are dried out.
You can either use the whole stalks for propagation or my preferred approach is to cut off the upper leaves for cooking, leaving behind roughly 3 inches of the stalk. This way, if it doesn't work out, I haven't wasted any.
Place the base of the lemongrass stalk into a glass filled with a little water (just enough for the base to be submerged).
The glass should be placed in a sunny spot indoors or in the greenhouse.
Change the water daily to discourage mould.
After a few weeks, roots will emerge from the base of the stalks. During this time, you will notice new leaf growth as well.
Lemongrass loves the heat and so tends to root better in warmer temperatures. The success rate can vary, ours was two out of three stalks. One stalk got mouldy even before it started rooting and so had to be discarded.