Well, "buying" spare seeds on Siege is a very iffy thing. Occasionally you will see some seeds on vendors, but not often. Siegers who read this will certainly understand! And if I can get this project off the ground, I vow that Camriel shall stock plant seeds on his vendors!
Like you, I let my plants go until the end before I harvest the seeds or other resources and yes, you are correct - Seeds of Renewal fetch a tidy sum of gold on Siege.
And that's what prompted me to consider this project in the first place. Since I'm going to grow plants anyway, for Seeds of Renewal, orange petals and the like, wouldn't it be cool to build a seed bank?
I do have access to other seeds within my guild. In fact, I believe that one other built a seed bank, but that was quite a while back and I only have occasional access to those seeds. Quite frankly, the other gardeners on Siege are always willing to share their seeds with others, as I learned before I started this 'personal quest.' (I needed a plain barrel cactus seed, and as soon as I posted a request on the Siege board, a kind soul dumped several of them in my mailbox.)
But I thought that this might be an easy in-game hobby that I could just quietly pursue without having to involve the entire shard! (It does seem as though a lot of the play on Siege involves the "entire shard" - and this is not a bad thing, by any stretch, but I didn't want to have to bother others.)
Thanks to all for the replies. Personally, I would hope that eventually the seed-crossing would be fixed. Maybe just leave one crossing that yields 'random' plants. But I don't know if others would like that or not. Others probably already have their personal 'seed banks' built.
At any rate, this will all be less frustrating knowing that I'm not actually crossing seeds, but "gambling"! lol.
It's still possible to get the Tier 3, but you will be better advised to buy spare seeds. The odds are 1 in 17 each time you roll with a cross breed with any of the random plants, as it can be any of the seeds including the Cactii etc you are after... but you'll need to beat those odds 15 times for each plant & colour type. (1 Plain and the 7 Colours in dull and bright)
I got close, but finished the set with seed trading; don't be afraid to offer every single seed you have to someone in exchange for just one you may need, and grow a tonne of the special poppies to get the poppy dust and identify any you find lying about or want to cut short... I personally let them all continue until all 8 seeds/resources are given, as Seeds of Renewal sell for a fortune, especially on Siege I should imagine!