Although the natural habitat of watercress is amongst slow moving bodies of water, their seed can be germinated in pots much like any other plants seed. In fact they are so easy to grow they can even be started off indoors. The only thing you need to make sure of – apart from keeping them soaked at all times – is that you are using an alkaline compost. This type of compost can easily be made up by mixing 1 part limestone grit to 2 parts John Innes seed compost.
Start by using plastic pots which have had small holes (approximately 3-4mm in diameter) drilled into the sides. Fill them with the compost mix and push 3 or 4 seeds – evenly spread - into the surface to around about an inch deep. Fill a suitable, high-sided container with water and place the sown pots into it. Leave the water level so that it is about ½ to 1 inch below the soil level. Place the container outside in a bright position, but out of direct sunlight and extremes of temperature. The important thing to remember here is to ensure the soil remains soaked at all times and to change the water for fresh each day to avoid fungal infections. You can expect to see the new seedlings emerging anytime from 7-10 days.