In PbP you translate Zeraim as seeds. But it seems from Rashi both here and also on 6b DH Mashkeh Mayim b'Zeraim that the meaning is Gidul Sadeh that don't need to be watered regularly.
Tuvya Marcus , Jerusalem Israel
Dear Tuvya,
The Rashi you mention does not mean growths that don't NEED watering- Rashi says that these growths have not actually been atered before te Moed and are therefore "used to" being without water.
Now Zeraim is a general term which means seeds and/or what grows from them; and if the words Shelo Shasu are added that adds that they weren't watered.
All the best, Reuven Weiner