I dont know if this will help but what I did was plant your seeds and remember which seeds do good in the begining and what seeds dont do good,The cross bred plants are tricky and dont do so well in nornmal soil, I would use the radioactive plant food to save some plants at the last minute, Harvest the seeds for later, Then just plant the ones that grow in the normal soil.Get the seeds replant again ect,ect,ect.
Just plant those all together, they sell better in groups,

It does take a little trail and error,.
When you price them, I just use the pricer and click up on the price about 3 times. Try this when you sell you'll get more for your plants.
then as you progress you can by the better water and soils.
It takes a little time, unless you want to play in fast mode.
I hope this helps..