Celery growing requires a good amount of sun – at least six hours a day. If it’s morning and afternoon sun with a shady break around noon, so much the better. A good way to increase light to the plants is to place your container near a white wall. Light-colored mulch such as white stones will also reflect more light onto the leaves.
Choose a container which is at least 8 inches deep and large enough to space the celery plants 10 inches apart. Don’t use an unglazed clay pot because it will dry out too quickly. Make sure there are drainage holes in the bottom. Fill the container with half soilless planting mix, half compost and a small amount of hard organic fertilizer. Mix well and water with a weak solution of fish and seaweed emulsion, Let settle for an hour. If necessary, top off with more moistened soil mix to leave 2 inches of headroom for mulch.
Celery plants should be firmed in well and watered with the fish and seaweed. Apply mulch to a depth of 2 inches. Make sure night temperatures are consistently above 55 degrees or the plants will bolt (go to seed). Celery is a real water-lover and will yield tough stalks if it dries out. It may be necessary to water twice a day during heat spells. If you can’t keep a close eye on your celery, then consider installing drip irrigation controlled by a timer.
The easiest way to grow celery is to buy transplants. If you decide to raise it from seed start ten weeks before you want to plant it outside. Celery requires light for germination, so press the seeds gently into the surface of the wet planting medium. I cover the pot with plastic wrap until the seeds sprout to prevent drying out. When the plants have at least two sets of true leaves, harden them off over a period of a few days by putting them outside a little longer each day then plant them outside in your container. Be sure not to expose them to temperatures below fifty degrees because this will trigger bolting (going to flower) later in the season.
Celery is a heavy feeder. Watering every two weeks with fish and seaweed emulsion should keep it growing strong. If the season is very rainy and watering is not an option, pull back the mulch and sprinkle on some high-nitrogen, dry organic fertilizer. The rain will wash it into the soil.
If you would like to blanch the celery stalks, slice a cardboard milk carton down the side and wrap it around the plant to shade it as it grows. But remember, green stalks have more nutrients. If they’re too stringy for fresh eating, I simply freeze the chopped celery in plastic bags and use it for home made chicken soup all winter long – delish!
Source: Johnny’s Selected Seeds