Answer: Bougainvilleas can grow to a rather substantial size so you'll need a large container or planter box. I'd recommend at least 18-24" deep and twice as wide. Bougainvilleas don't seem to mind growing in Mesa's alkaline soil but a planter box or large container of native soil will be very heavy. For this reason, I'd suggest mixing potting soil in with the native soil. A half and half mixture will provide the weight your top heavy bougainvillea will need to keep it from toppling over in the winds but will also provide good drainage for the root system. You can feed your bougainvilleas every 6-8 weeks with a half strength dilution of a liquid fertilizer (Peter's, Miracle Gro, etc.). By diluting the fertilizer to half strength you'll avoid salt build up in the container and you won't risk burning the roots when you feed.
Best wishes with your bougainvilleas!
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