You can breed a female with these to have Leech Seed:(that is if they are level enough and you hv retained leech seed)
Bulbasaur >>>>>Male
Ivysaur >>>>>Male
Venusaur >>>>>Male
Exeggcute >>>>>Male
Hoppip >>>>>Male
Skiploom >>>>>Male
Jumpluff >>>>>Male
Sunkern >>>>>Male
Sunflora >>>>>Male
Shroomish >>>>>Male
Breloom >>>>>Male
Roselia >>>>>Male
Cacnea >>>>>Male
Cacturne >>>>>Male
Turtwig >>>>>Male
Grotle >>>>>Male
Torterra >>>>>Male
Cherubi >>>>>Male
Cherrim >>>>>Male
Snivy >>>>>Male
Servine >>>>>Male
Serperior >>>>>Male
Cottonee >>>>>Male
Whimsicott >>>>>Male
As you get a new female Ferroseed, breed it with these if they know Spikes:
Cacnea
Cacturne
Source:
http://pokemondb.net/pokedex/ferrothorn/egg#move-leech-seed
