This is, without question, the single most important step, and it doesn’t involve any ingredient at all, just consistent habits. Fix leaking taps, wipe down counters and stovetops after cooking, store food in airtight containers, and empty the kitchen bin daily rather than letting it sit overnight, since cockroaches are drawn overwhelmingly to accessible food and standing water. Sealing visible cracks around pipes, baseboards, and door frames closes off the entry points roaches use to get in in the first place, making every other natural method on this list considerably more effective.