Certified Professional Horticulturist (CPH) Practice Exam

During active growth, how much water do most trees, gardens, and lawns need per week?

1. 1 inch

2. 10 inches

3. 3 inches

4. 1 foot

The correct answer is: 1 inch

The amount of water that most trees, gardens, and lawns need during active growth is typically around 1 inch per week. This figure is well-researched and is generally recommended as a guideline for adequate irrigation under normal weather conditions. An inch of water applied to the soil penetrates to a sufficient depth to reach the root zones of most plants, ensuring they can absorb what they need for growth, without the risk of over-saturation or wastage. Other choices such as 10 inches, 3 inches, or 1 foot greatly exceed the typical requirements for watering and may lead to issues such as waterlogging, nutrient leaching, and root rot. These excessive amounts can cause more harm than good, leading to decreased plant health and sustainability in landscaping practices. Using 1 inch as a standard helps create a balance where plants receive the correct amount of moisture, promoting healthy growth and efficient water use. This guideline can vary based on specific plant types, soil conditions, climate, and other factors, but it remains a foundational principle for effective horticultural practices.