Spelling the “Seed” Sound
It's easy to remember how to spell the "seed" sound when the word refers to seed that comes from a plant. That "seed" sound is always spelled s-e-e-d: birdseed, cottonseed, flaxseed, linseed, poppyseed, pumpkinseed, and so on.
But what about the other "seed" sounds?
Only one English word ends in sede: supersede.
Three English words end in ceed: exceed, proceed, and succeed.
All other English words that end in the "seed" sound are spelled with cede: intercede, precede, recede, secede, and so on.
See also: Guide to Spelling.
More on Spelling the Seed Sound from Fact Monster: