Nasturtium officinale.?True Watercress seeds produce a perennial cress that is rich in vitamins and has a delicious, distinctive taste for salads and vegetarian dishes. Little, dark-green leaves grow on crisp stems that come from thick, long roots. Direct-seed watercress about 5mm (1/4″) deep and 1cm (1/2″) apart, ideally in full sun near clear running water. Thin plants to 10cm (4″) and keep very well watered. Watercress does not thrive in acidic soil, so spread enough lime in the growing area to bring the pH as close to 7.0 as possible. Well finished compost is the other trick that will keep watercress growing rapidly. If you fail with watercress in your summer garden, try planting it beneath a cloche row cover for winter harvesting. The low light levels and cool temperatures seem to be ideal.