Your three answers are connected. Soil pH can be impacted by the quality of water used to irrigate your plants. Iron deficiency is directly related to pH. Holly prefers an acidic soil pH which would allow for iron uptake naturally by the plant. If your water pH is alkaline, this is raising the pH of the soil. If you treated the foliage with a liquid iron and in 24-36 hours the foliage turned green, iron is the answer. Feeding the plants is really treating the symptom though. You should acidify the soil profile around the plants with a sulfur compound and amend the soil with organic matter. Suggest a soil test to determine the actual pH and adjust according. Contact your local Extension Office for a more localized and focused recommendation
