Yes, it extends the bloom. Sweet pea plants come to the end of their flowering life whether you deadhead or not, but you can prolong the bloom period by cutting off spent flowers.
Or, many would say cut them off before they are spent and enjoy the flowers in a vase or pass along bouquets, but whether you cut them at their prime or past it, deadheading will extend the bloom time.
morz8 - Washington Coast
kwyet1Original Author