How big is the backyard? Blackberries are brambles and become large, sprawling plants in a single season, even when pruned back in winter. And you need at least two different blueberry shrubs for the best cropping. So one or more of each may not make a lot of sense in a small garden.

Blueberries come in a range of sizes so it would much simpler to just focus on a couple of those in dwarf or compact sizing. I don't even know what a chigger is but these are cultivated - not wild - plants so what sort of pests might be present in a wooded setting are unlikely to bother or be present on a plant in a cultivated garden

I've grown blueberries, blackberries, and raspberries in the backyard and chiggers were never a problem. That said I kept the plants heavily mulched so there was never any tall grass that I usually associate with chiggers.

Thank you Adam for giving me the possibility of adding berries to my small garden. Originally I planted lots of perennials, knockout roses, and I have a passion for Japanese maples. Now as 4 years have past I'm adding more edibles and want to give the space a looser feel. The area I was thinking about adding some berries is a raised stone bed that has always been mulched.