A lot of it is the soil. Adding fertilizer and sterilized manure before planting helps. Neem oil is a great way to keep the pests away, is organic and natural. I have to spray about once a week to keep aphids and spider mites away. Automatic watering systems help too, if you have one. I have a very rare thing for around here, the house came with a well for irrigation which you can't get permits for anymore, so I was lucky!