Please give me a detailed and complete guide on how to grow/plant celery.
This article will help you with that: https://www.gardeningknowhow.com/edible/vegetables/celery/tips-on-how-to-grow-celery.htm
What fertilizers do you use for growing celery plants?
When you plant them, give them balanced and complete fertilizer and again in about 6 weeks. Another month after that, fertilize them with a nitrogen rich fertilizer.
Does celery seed need light to germinate?
Thanks for your advice.
Celery does not require light to germinate. However, they are a bit finicky and can take up to three weeks to sprout. Just barely cover the seeds and be sure to keep them moist. Celery seeds also have a higher percentage of germination when a lower temperature is maintained.
Can you plant celery from the stalk?
No, unfortunately you cannot root the stalk. You need to start it from seed.
I read the article on growing celery and it says not to plant out until temps are over 50 degrees. Is that daytime, nighttime, or both? Also, is there a preferred temperature for the soil to reach before planting out?
That is the daytime temperature. Also, celery requires at least a soil temperature of around 59-60 degrees F.
We planted celery and it's getting pretty tall and has yellow blooms, but we don't know where they should be picked off or just left alone. We don't know what it is supposed to look like and when is it ready.
Your celery has bolted. Harvest celery as soon as it's large enough to use. Either cut off individual stems as they develop color or pull the entire plant and cut off the roots. Celery should be harvested when the petioles (stalks) from the soil line to the first node are at least 6 inches long. These articles will help: https://www.gardeningknowhow.com/edible/vegetables/celery/tips-on-how-to-grow-celery.htm
For the temperature, is it that it should be above 50 for the low of the day before putting out the plants? I have grown celery before, but it got very bushy and leafy.
Celery does best in cool weather when nighttime temperatures are around 50 degrees F. and average daytime temperatures stay between 60 degrees to 70 degrees.