After a warm and dry spring and start to summer, an unprecidented heatwave, and anticipated continued dry conditions for several more weeks; many of us are concerned about keeping our plants alive. This guide to proper watering shared with us by local horticulturist Tom Del Hotal will help you better understand the needs of your plants, and to use water more efficiently.

 Keys To Proper Watering

By Tom Del Hotal

One of the most common causes of plant death or poor plant performance is the misunderstanding of what is meant by proper watering. This becomes a more significant issue when the weather conditions become drier and hotter and rainfall must be supplemented or replaced with irrigation water.  

Questions about irrigation that are commonly asked are: What is the best type of irrigation system to use or what is the best way to water my plants? How long do I water or how much water do I give my plants at each watering or irrigation cycle? How often should I water my plants? 

There is no one way to correctly water plants. Any method used to water plants, such as a bucket, a hose, flood irrigation, sprinklers, bubblers, a drip system, micro-spray or any other watering method can be used to properly water as long as 4 principles are followed.

Since a plant absorbs water (in most cases) through its root system, we need to understand what is going on below the ground and what are the primary functions of a plant’s root system.

The root systems on plants have 3 main functions.

One function is to anchor the plant so that it stays upright in the soil or growing medium. 

A second function is to store food and carbohydrates to sustain the plant during the dormant season or when the leaves are removed or are lost from the plant’s canopy. (This is especially true on deciduous plants during the period when there are no leaves on the plant or when a plant is heavily pruned.)A third function is to absorb water and nutrients. The roots that absorb water and nutrients are called feeder roots or hair roots. These very fine, delicate roots are constantly being generated and are constantly dying off due to soil conditions and other factors. Water absorption by an established plant in the ground occurs primarily within the Feeder Root Zone.

A plant’s root system needs both air and water for survival and healthy growth. Soil conditions that are too wet exclude available air and roots may drown or be killed by fungus diseases. Soil conditions that are too dry may lead to plant wilt, plant desiccation and root or plant death. A careful balance of water and air in the soil must be maintained for best plant growth and development. During dry weather this balance must be maintained by proper irrigation methods.                          

The 4 key principles of proper watering are:

#1  Water the proper area – the Feeder Root Zone!

•           Water near the trunk or stem on newly planted plants so that you thoroughly wet the original root ball.

•           Water slightly inside the drip line and well beyond the outside of the drip line on plants that are established in the ground. (The plant may take from a few weeks to one year or more to become established depending on the type and size of the plant, the time of year that it was planted, soil conditions, cultural practices and other variables.) 

•           Water farther away from the trunk or stem as time progresses, as the plant grows larger and/or the plant’s canopy expands in diameter.

#2  Apply water to a sufficient area of the Feeder Root Zone to support the canopy of the plant and to maintain a strong and healthy root system.

•           Irrigate as much of the area around all sides of the plant as possible, not just one side or in one area.

•           Water will spread out to an average of 1-2 feet at a depth of 2-3 feet when applied from a source such as a drip emitter or soaker hose.  

•           If irrigating with a drip system or with soaker hoses, provide enough drip emitters or concentric rings of soaker hose to wet a significant area of the Feeder Root Zone – NOT just a few spots or a single line.

•           Adjust and expand the region irrigated as the plant grows to promote the expansion of the root system into the surrounding soil. In order to support the healthy development of the plant’s canopy and for the plant to grow larger it must have a larger root system.

#3  Apply a sufficient amount of water – enough to thoroughly wet the entire depth of the Feeder Root Zone.

•           1 inch of water penetrates the ground 1 foot in sandy soil, it takes 2 inches of water to penetrate the ground 1 foot in clay soil.

•           90% of feeder roots are found in the top 3 feet of soil! (Of that 90%, 70% are in the top 1 foot of soil.)

•           Water to an average depth of 1 foot to 3 feet at each watering for plants that have been established in the ground. Smaller plants generally have shallower root systems than larger plants. As a general rule, water to a minimum depth of 6 inches to 1 foot for plants 1 foot or less in height, to a depth of 1-2 feet for plants 1-5 feet in height and to a depth of 2-3 feet for plants larger than 5 feet in height. •           For plants in containers, thoroughly wet the entire root ball and the surrounding soil in the container. At each watering use enough water to leach excess salts out of the bottom of the container. 

#4 Water at the correct interval – often enough to keep the plant from wilting, but infrequently enough to allow air to penetrate the soil. Roots can drown if the soil is kept constantly wet!

•           Watering frequency will vary with the time of year, location, size of the plants, soil, weather conditions and many other variables.  

•           On average:

•           Water new plants in the ground 1-3 times per week. 

•           Water older established plants in the ground 1 time per week to 1 time per month depending on the above stated variables.

•           Water plants in containers 1-3 times per week.

 Frequent light (shallow) watering will promote a very shallow root system on a plant because sufficient water will often be unavailable deeper in the soil. Also, if the surface soil is kept constantly wet, sufficient air may not be able to penetrate deeper into the soil. A balance of both water and air in the soil root zon is necessary to promote deeper root growth. •           There are very few exceptions where plants should be watered every day! Watering too frequently will exclude oxygen from the soil and cause roots to drown as well as promote diseases!