
Lemongrass is a useful plant that can be used in cooking and to make refreshing lemongrass drinks. It is also a natural mosquito repellent. The good news is Lemongrass is very easy to regrow.
Regrowing Lemongrass in 2 Weeks
We bought some Zenxin brand organic lemongrass from the supermarket (available in Giant or Cold Storage in Singapore) to make Tom Yum.
We cut the top off to cook with and kept the bottom 2 inches to regrow.
The lemongrass was placed in a container with water, which was changed every 2 or 3 days (or whenever I remembered). Many plants can be placed in water initially in order to root the plant. These include bulbs like lemongrass and spring onions, and stem cuttings from plants such as kangkong, mint and basil.
Day 0:

12 Oct 2016: These 2 inch long lemongrass pieces were placed into a recycled cotton bud container with a little water.
Day 2:

14 Oct 2016: After 2 days in water, the lemongrass is starting to regrow shoots. Look carefully and you can also see a little root growth.
Day 4:

16 Oct 2016 (Day 4): The lemongrass has grown roots as well as shoots.
Day 6:

18 Oct 2016: It's day 6. More roots and shoots are growing.

18 Oct 2016: Here's another view that shows the root growth by day 6.
Day 13:

25 Oct 2016: Here's the lemongrass plants after 13 days in water. As you can see, they've grown quite a lot in less than 2 weeks!

25 Oct 2016: Here's a look from the bottom. You can see that the roots have grown much more.
Day 14:

26 Oct 2016: After exactly 2 weeks, 3 out of the 5 lemongrass stalks have lots of roots. 1 has a few short roots and the final stalk has no roots.

26 Oct 2016: After 14 day, I transplanted 2 of the lemongrass stalks into potting soil. I left 3 in water because I'm curious to see how the growth in soil compares to water.
So in just 2 weeks, the lemongrass has regrown significantly. This is once of the easiest and quickest plants to grow from what would otherwise be discarded kitchen scraps.
Another good thing is that you will have a virtually unending supply of lemongrass. Just cut off what you need and the lemongrass will keep regrowing!