Successfully growing celery (Apium graveolens L. var. dulce) in the home garden is quite rewarding because it's a tricky plant to grow. Celery is a cool-season plant, but it is very picky about the temperature range it grows in. It also requires evenly moist soil, the appropriate pH levels and plenty of growing time.
In North Carolina, the last frost date falls from mid-April to mid-May. Celery cannot be planted outside until all danger of frost has passed because it will try to set seed if the temperature falls below 40 or 50 degrees Fahrenheit for several days. Planting earlier is possible as long as you are careful to cover the young plants if the weather turns unexpectedly cool.
If you plan to grow celery from seed, start them indoors at least 10 weeks in advance. For most parts of North Carolina, start celery seeds indoors in mid-February to early March so that they're ready to plant at the beginning of May. The seeds are quite tiny, so you may want to simply put a small pinch in each starter pot. Once the seedlings emerge, thin them by clipping extras at the soil line so that you don't disturb the roots of the one you're keeping.
Before planting celery outside, test your garden bed's pH levels. Celery prefers its growing medium to have a pH range of 6.0 to 7.0, which is slightly acidic to neutral. If needed, amend the plot with compost and organic matter to ensure the best possible growing conditions. Plant the celery seedlings 1 foot apart in all directions if you're placing them in a bed; or, 1 foot apart in rows that are 2 1/2 feet apart.
Celery requires three to four months of growth time in addition to the initial 10 to 12 weeks head start it had indoors. The soil must be kept evenly moist during the entire time, so it helps to mulch around the plants. Several inches of hay, grass clippings, newspaper, sawdust or coarse wood chips are suitable mulches that help maintain soil moisture levels.