I do a lot of gardening, and all the seed a mars mission could ever use would weigh less than a KG. I think we should just abstract the seed count away and call the seed bin a seed starter, and just leave it at that and not even track seed anymore..
Also with hybrid plants, you cannot use the seed from the children most of the time, they will have genetic characteristics that are not correct.
The plants, when planted are also obviously not from seed, and instead are from a seed starter.
Maybe if you still wanted to keep a limit on the seed, make it so the seed starter produced 5 plants of each type every day or something... But I dont think that is really necessary if the limit of not being able to harvest anything before a certain time is put in.
*This change would correct two realism things.
#1 each plant would likely produce enough seed to make 40-1000 new plants (40 for potatoes, 1000 for zucchini)
#2 The weight of seed for everything but potatoes would be nearly irrelevant on a martian mission, they could send probably close to a million zucchini seeds in a KG.