1. Question: According to the Rashash, why would you be liable for planting a mixture of seeds as soon as you put it into the ground but only liable for transgressing planting on Shabbos if you allow the seeds to take root?
A. Rashash holds that just as one is only liable for baking on Shabbos if it actually baked but not if one put a raw dish in the oven and took it right out so too if one planted a seed on Shabbos he is only liable if he let it takes root not if he took it right out after he planted it.
B. The Sefer HaChinuch (mitzvah 548) says you are liable for planting a mixture of seeds as soon as it goes into the ground even before it takes root. (Unlike Rashi in Pesachim 25a who says that as long as it has not taking root, it’s like just placing two seed into a cup.)
C. The Rashash who holds by planting on Shabbos that one is only liable if it takes root seems to hold that by a kilayim mixture just planting it is a problem according to everyone why would there be a difference between kilayim and Shabbos?
Answer: To transgress Shabbos one has to do a meleches machsheves, an action which produces a creative result therefore one is only liable for planting once it takes root or has the ability to take root since it stays in the ground, whereas by kilayim, forbidden mixtures the very action of setting up a forbidden mixture is enough to make you liable.