Because giant celery has such a long maturity time, giant celery needs to be planted at the beginning of January in a heated greenhouse. Because you will be starting off your giant celery seed under protection, you will need to use either 3 inch pots or large module trays filled with a good quality seed compost such as John Innes ‘Seed and Potting’. Like normal celery seeds, giant celery seeds are tiny and tricky to plant, so try mixing them up with some horticultural sand first and then sprinkling the sand/seed mix over the pots or modules that you are starting the celery plants in. This will help you to identify them.
Cover the seeds with just a thin layer of soil as giant celery seeds definitely like to be planted shallowly. Gently water in, you may wish to sit the tray / pots in a pan of water and allow the water to rise through the compost using capillary action.
Once watered, cover the pots/ trays with a transparent cover - sheet of glass, cling film, or propagator lid and transfer to a warm bright position. Just make sure that it is out of direct sunlight. Once the seeds have germinated you can remove the cover, and now water as necessary.