KC Gardens

How to know when your landscape plants need a drink

Knowing when to water, and how much, is one of the most difficult gardening lessons to learn.
Knowing when to water, and how much, is one of the most difficult gardening lessons to learn.

Water is the basis of life. All living things depend on it, including our landscape plants. Improper watering is probably the No. 1 killer of plants, as we often apply too little or too much. Yet learning to water properly is one of the most difficult gardening lessons.

Why is something so basic so hard? The problem is simple: We cannot see what is going on 6 to 8 inches below the soil, so we are left to guess whether the plant needs to be watered. Learning the principles of watering is the first step.

Watering is about keeping the plant’s root zone hydrated. Roots develop from just below the surface to many feet deep into the soil, depending on the plant. The majority of plants, whether a stately oak tree or a tomato plant, have feeder roots to pick up the water, mostly in the upper 6 to 8 inches of the soil.

That’s why we focus on watering in this shallower layer of the soil. However, some plants can pick up water more deeply in the soil, some drought-tolerant plants can survive on less water, and others need a consistent level of moisture. That is part of the problem when learning how to water.

Another factor is finding the proper combination of oxygen and water in the soil for the roots to survive. Creating this balance results in the best growth. More water in the soil means less oxygen; less water means more oxygen. If either is off, then the plant can show signs of wilting.

Based on the location of the roots and air exchange, I recommend watering deeply and less frequently. Soak the root profile 6 to 8 inches deep and do not reapply until it has dried out. This method follows the standard recommendation that plants need about 1 inch of water about once a week.

It takes an inch of water to soak our clay soils about 6 to 8 inches deep, and under normal conditions, a week to dry out. Of course there are variables such as rainfall, heat and wind that make watering confusing.

The best way to know when to water is to dig down a few inches in the soil around the plants. If it feels moist, don’t water; if it feels dry to the touch, water. How simple is that? As you become more experienced, it almost becomes second nature. Don’t be afraid to get your hands dirty and learn your soil and plant needs.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org.