[Marileangorifurnimaluim]

Jessica, I think it's unlikely Sauron directed Saruman to take over the Shire. It was Saruman's own mean-spirited idea.

The take-over of the Shire (and all the trouble in the areas around Bree) had to come after the Rangers left for war (right around the time of the battle of Helm's deep). Until then the Rangers protected the borders of the Shire.

Yet only days after Helm's Deep, Wormtongue chucked the Palantir, Saruman's only source of communication with Sauron, at Gandalf. It's too narrow of a window of time to learn the rangers were gone, receive instructions, and then gather thugs to send west, plus it would have taken forces away from Saruman's attack on Rohan. Both Sauron and Saruman would have considered the Shire a minor matter easily dealt with at their leisure. Once they were victorious.

Now Saruman did have previous connections with the Shire (recall the barrels of Longbottom Leaf found in the wreckage of Orthanc), and had learned of its connection with the ring in the summer before the battle of Helm's Deep.

But he had no reason for revenge until the attack of the ents. He would have seen Merry and Pippin with ents during and after the attack on Orthanc, and in the manner of bullies everywhere, decided to take his revenge on the weakest, easiest target. With the fall of Sauron that wish for revenge would have redoubled, against Frodo.

He had plenty of time after the end of the war of the ring to wreak havoc. The war ended in the Spring, but the Hobbits didn't return to the Shire until mid-fall.