I have a fourth-floor balcony that only gets sun until 2 PM, and I'm trying to figure out if petunias can still grow well anyway. I'd like to grow them in large pots, but I'm not sure how often to water them in this July heat.
Petunias in pots do just fine with sun up until 2 pm, even though ideally they'd prefer more hours of light - but they'll still grow, maybe just with a bit less abundant flowering.
In large pots (say 30-40 liters) the soil retains more moisture, so with this July heat you should water when you see the top 2-3 cm of soil are dry, probably every 1-2 days depending on how much direct sun hits it and the humidity; it's better to check with your fingers rather than stick to a fixed schedule.
Use good potting soil with drainage, otherwise you risk waterlogging that'll kill them, and if you notice the leaves starting to lose color from the edges you're probably watering them too little or the pot's too small for proper evaporation.
Don't let them suffer from drought - that's the most important thing in this heat. In July, water almost every day, maybe in the evening when the sun isn't beating down anymore, and make sure the soil doesn't dry out completely. Sun until 2 PM is fine, they'll grow normally anyway, maybe just a tiny bit fewer flowers compared to a plant in full sun, but nothing to worry about.
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