An easy way to start your watercress plants is propagate from shop bought watercress. You can use watercress that comes in salad bags - if you look carefully, you will see that some of the stems will already have tiny roots emerging.
To get new cuttings: 1. Trim back watercress stems into small cuttings, leaving just a few leaves on each. The idea is that you don't want them to be too top heavy with a lot of leaves so that the stems can concentrate on growing roots.
2. Place the stems in a little water - you don't need too much water, just enough to partially submerge the base of the stems.
After a few days, you will notice roots on your watercress stems. You should also see new leaves start to emerge and grow.
Your watercress is now ready for planting.