There’s no single number that works here, and anyone who gives you one without asking about your pot size, material, and exposure is guessing. A 6-inch terracotta pot on a west-facing high-rise balcony in July might need water twice a day. The same plant in a 16-inch glazed ceramic pot on a shaded ground-floor balcony …

A reader wrote in a few weeks back asking why her balcony tomatoes needed water almost every single day, while the same variety in her sister’s backyard garden went two or three days between waterings without wilting. Same seed packet, same fertilizer, similar sun exposure by her estimate. She wanted to know what she was …