I encourage spiders in my garden. Truthfully, I can't really keep them out, as I grow in a greenhouse which has a certain degree of porosity for insects. This is actually good, as it keeps a living balance of predator and prey, and prevents any infestation, which is just a dinner bell for the predators. I like to bring in praying mantis and spiders I find about the outside garden. A population of toads and bats about the grounds does backup duty as well. I know, it sounds like Hagrid's grow op... but spiders and such critters evolved to eat pests!
I spray (neem + bronners peppermint + hot pepper extract), during veg, but after a week or two into flower I just do spot treatments and remove bugs manually. If a plant seems to be ailing, I move it outside, which compared to the greenhouse is like a wild jungle; those soft city bugs don't last more than a week out there... Once on my indoor grow I had a run that got attacked by mites; one plant got really bad, so I removed it from the grow and put it outside as a write off. I figured I could control the mites in the limited space of my garden... nope; I couldn't keep ahead of them. I probably could have used a heavy chemical spray, but I smoke my own grow, so I ended up cutting down the indoor garden. The plant outside, which I didn't do I thing to, finished out like a champ and had better yield from being left to go outside.