The duration for watering a tree with a hose is a calculation based on the specific volume of water the tree needs and the rate at which the hose delivers it. The goal is to achieve deep saturation of the root zone, typically 12 to 18 inches below the surface, rather than simply wetting the topsoil. To accomplish this, the hose must be set to a slow, deliberate trickle or use a soaker attachment, allowing water to soak in gradually without causing surface runoff. This slow, deep watering encourages a robust root system that can withstand drought effectively.
Determining the Water Volume Needed
Water must penetrate to the depth where the tree’s fine, water-absorbing feeder roots are most active, generally in the top 12 to 18 inches of soil. Avoid light, frequent sprinklings, as they only moisten the surface and encourage shallow root growth susceptible to heat and drought stress.
A practical guideline for estimating volume is to measure the diameter of the tree’s trunk, known as the caliper, at about four feet above the ground. Established trees generally require approximately 10 to 15 gallons of water for every inch of trunk diameter during each deep watering session. For instance, a tree with a four-inch caliper would need between 40 and 60 gallons of water to adequately soak its root zone.
Soil composition influences how much water is needed and how quickly it should be applied. Sandy soil drains rapidly, requiring the total volume to be applied in smaller, more frequent increments to prevent drainage past the root zone. Clay soil absorbs water very slowly but retains moisture longer once saturated. A slow trickle is necessary with clay to prevent surface runoff.
Measuring Your Hose Flow Rate
The next variable is the rate at which your hose delivers water at the low-flow setting you plan to use. Since deep watering requires a slow, controlled release to prevent runoff, measure the flow rate at this reduced pressure, not at the full blast setting. This rate is measured in gallons per minute (GPM) using a simple “bucket test.”
To perform this test, use a container of a known volume, such as a five-gallon bucket. Set your hose to the slow trickle or low-pressure setting you intend to use, and time how long it takes, in seconds, for the hose to completely fill the bucket.
This measurement allows you to determine the flow rate in GPM. For example, if it took 600 seconds (10 minutes) to fill the five-gallon bucket, the flow rate is calculated as five gallons divided by 10 minutes, which equals 0.5 GPM.
Calculating the Watering Duration
The total watering duration is calculated using the formula: Total Volume Needed divided by Flow Rate equals Watering Duration. This calculation provides the specific amount of time the hose must run to meet the tree’s water requirement.
For example, consider a four-inch caliper tree that requires 60 gallons of water for a deep soak. If your slow-trickle flow rate is 0.5 gallons per minute (GPM), the calculation is 60 gallons divided by 0.5 GPM, which results in 120 minutes. This means the hose must run for two hours to deliver the necessary moisture to the tree’s root zone.
For a larger tree, such as an eight-inch caliper requiring 120 gallons, the duration would double to 240 minutes (four hours) using the same 0.5 GPM trickle. This long duration highlights why deep watering is a periodic, rather than daily, task.
Place the hose or soaker attachment on the soil surface at the tree’s drip line—the area beneath the outer edge of the branches—where the majority of water-absorbing roots are located. For larger trees requiring several hours of watering, move the hose to a different spot along the drip line every few hours to ensure even saturation.
Watering Frequency and Seasonal Adjustments
The duration you calculate determines how long to water during a single session, but the frequency depends on the tree’s age and environmental factors. Newly planted trees require more frequent attention because their root systems are confined to the original root ball and have not yet spread into the surrounding soil. For the first few months, a new tree may need watering every two to three days, with the frequency gradually decreasing as the tree becomes established.
Mature, established trees benefit from deep, infrequent watering, which encourages the roots to grow deeper, making the tree more resilient to dry conditions. These trees typically only need a deep soak every two to four weeks during the growing season, especially in the absence of significant rainfall. The exact interval is dependent on local weather conditions, such as high temperatures and drought periods, which will increase the water demand.
Before initiating a deep watering session, check the soil moisture by pushing a probe or long screwdriver six to eight inches deep near the drip line. If the probe slides in easily and the soil feels cool and moist, the tree does not need water; if the soil is dry and resists the probe, apply the calculated volume.