Answer: It may be related to water availability. Like most annuals, petunias prefer evenly moist soil (never soggy or completely dried out) and under- or over-watering can lead to brown edges.
Another common problem is fertilizer burn. Always apply fertilizers according to the directions on the label, taking care to dilute them properly. Fertilizer salts can build up in containers, so flush the soil monthly by applying lots of water and letting it drain through. In general, petunias prefer full sun, evenly moist soil and a consistent supply of nutrients. Provide these and they should give you bountiful flowers in return.
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