Celery can be a difficult plant to grow as it requires a long growing season and if transplanted to the garden too early, exposure to cold will cause it to bolt (divert resources to producing flowers and seed instead of leaves). If you have got the stems to 1 ft then I assume this has not been a problem for you! I’m somewhat confused by your question as if you are not doing so already then you can certainly be harvesting the petioles (or stalks) which would mean that you are cutting them back naturally. There is no need to wait until the plant reaches the height yours has.

Do you perhaps refer to cutting the plant back for overwintering? Celery is usually grown as an annual plant and, after harvesting the stalks, it is grown anew from seed the following year. However, celery is actually a biennial species and you can try to overwinter it for a second period of growth the next year. If you wanted to do this then yes, it would be necessary to cut back the stalks as you suggest. However, your ability to overwinter celery will depend largely on where you are located geographically. The stump may not survive very hard cold. If you have a fairly mild winter, it may be possible to cover the stump and protect it that way. Another option would be to carefully dig up the stump and overwinter it indoors. Given your success at growing the plant, I’d be inclined to suggest just starting afresh next year.

In addition, you can blanch celery a couple of weeks prior to harvest to prevent the stems from becoming bitter (although some people prefer it). Blanching involves covering the stalks with paper or soil to prevent them from turning green. You can simply tie paper (newspaper works well) around the stalks from the ground to the base of the leaves, or you can begin slowly mounding the soil starting 2-3 weeks before you plan to harvest.