The best distance between plants is depending on the variety 50 cm x 40 cm to 40 cm x 40 cm.
So you only plant on a normal bed 3 Rows. You can also plant on cucumber beds with good success. At the same time lettuce is cultivated on the cucumber bed, then you plant the celery, for example 10 cm from the edge of the bed, while in the middle between celery- and row of cucumbers the lettuce stands. The salad is omitted, then the celery rows will be about 20 to 25 cm away from the bed edges.