Spiders: Spiders help keep the pest population at bay, but too many spiders can be unnerving—to say nothing of the poisonous ones. Diatomaceous earth is effective because as spiders walk across it, the razor-sharp microscopic fossils penetrate the exoskeleton, causing the spider to dehydrate and die. Suggested spider repellents include essential oils such as tea tree, cedar oil, eucalyptus, citronella, and peppermint.
Aphids: Spray streams of water onto plants to dislodge heavy concentrations of aphids. Use a mixture of castile soap, cedar oil and water to spray on smaller concentrations; the soap will dry out their exoskeleton and dehydrate them. Garlic spray can also be effective.