"From what little I have read that is a long distance for a drip system"

OK ... this by it self makes no sense ... so forget what you read ... How much flow you need versus distance is what you need to look at ... regardless of what kind of system you design. A drip system is not defined by the type of plumbing you use to carry water but the type and size of plumbing will determine your pressure loss over the six hundred feet distance.

What you need to do is decide how many drip emitters you will need for all your Thuja ... then add up the total flow reqired by all the emitters.

Example : If each tree has four emitters at 1 gallon per hour ... all running at the same time is 920 gallons per hour but that converts to 15 gallons / minute.

This is not a lot of water to deliver but you will need to run PVC ... not 600 feet of 1/4 inch polly !! .. right ?? In fact polly pipe can be avoided completely as this will give your system better integrity. If your longest run was 800 feet .. using 1 1/4 and 1 inch PVC should work out well ...

By the way a system like this is designed to run several hours at a time ... the point of drip is slow application rates.

Good Day ...

when doing a system like this I would trench alongside the bed and lay 1 1/4 inch pvc and stub it up 3-4 times, tie that into the dripline at each stub.

and yeah, what Mohave says bout flow