One difficulty with celery is deciding how much to plant. Utah State University's extension service suggests five to 10 plants per person in the household, but this may be excessive. Given that the outer stems can be harvested steadily through the growing season, 10 to 12 plants should provide as much celery as an average household can reasonably consume while it is fresh.
Most guides suggest planting celery from transplants rather than seed, and using a spacing of 6 inches between plants. Assuming conventional rows and 10 to 12 plants, this would mean a 5- to 6-foot row, with the space between the rows being wasted. Home gardeners with small plots are better advised to plant in raised beds, where 12 plants can easily be accommodated in just 2 square feet.
Mark out 2 square feet of your garden with string. When the your usual last-frost date has passed, set your first transplant in the top left corner of the first square foot. Set the second 6 inches down the left side. Next, use a 6-inch ruler to place a third transplant in between the two, 6 inches away diagonally from the first pair. Your fourth should be 6 inches below the third. Repeat measuring and planting until all of the transplants are spaced and in the soil. Water them well, and use row covers if the nights are cold.
Celery needs well-drained soil and lots of help to grow properly. It has shallow roots, requiring plentiful fertilizer and watering. It also competes poorly with weeds, though intensive planting helps reduce the work involved in weeding. Some growers keep their celery pale and mild by wrapping it in straw or other mulch as the season progresses. Harvest outer stems through the season as needed, and whole plants once they reach 3 inches in diameter. Celery stores well for a few weeks, and can be dried or frozen for use in soups or casseroles.