Answer: You'll need to do a little research on the mineral components of grape juice and apple juice to determine if they have more minerals than your tap water. Then you'll want to find out the pH (measure of alkalinity or acidity) of your fruit juices to see if they are acidic or alkaline enough to change the pH of the soil. If either is acidic or alkaline enough, they can alter the soil pH and cause certain nutrients to become 'locked up' and unavailable to the plant. Usually the symptoms of mineral deficiency are yellowing leaves, stunted growth, and general poor performance.
Because different plants have different pH requirements, the effect on the plant would differ depending on how tolerant the plant is of acid soils.
For instance, green beans will grow in a neutral to slightly acidic soil (pH range from 7 - neutral - to 6.0, which is slightly acidic). Apple juice is very acidic (about 4.0 on the pH scale) and grape juice is about 3.8). So if you grew green beans in alkaline soil, and you watered them with fruit juice, the juice would lower or acidify the soil which would make the green beans happy. But, if you grew cactus in alkaline soil and watered them with fruit juice, they would not grow well because cacti prefer alkaline soils. Hope this information helps!
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