May be sown from April 15th till June 15th.  Sow seed 1/2 - 3/4 in. ( 13 - 19 mm ) deep, in a sunny location.  Thin seedlings to 4 in. ( 10 cm.) apart when they are about 2 in. ( 5 cm. ) high. Pull every other plant for early summer use, so that remaining plants are 8 in. ( 20 cm. ) apart.  In early August, trim off all the old leaves, and give the row a light side - dressing of a high nitrate fertilizer - you can have fine "greens" till frost.  Plants must be watered during dry periods to prevent tender celery - like stalks from becoming woody.  Savoyed leaves are harvested throughout the season as a "cut and come again" vegetable, they are cooked like spinach.  Outer leaf stalks make delicious "fritters".  Mid ribs are eaten like celery or rhubarb.  Plants withstand hot summer temperatures - a delicious way to grow alternative to Spinach.  Where Spinach bolts to seed - Swiss Chard keeps right on producing.