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Water, Water Everywhere!—Watering Suggestions for Outdoor Plants in Colorado

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Isn’t it fun to spend an hour or two on a Saturday morning, cup of coffee in hand, watering our outdoor plants with a hose and watering wand? Of course, but if you are like me, you do not have the time or patience to do that every weekend as the plants require. Therefore, it is an inconsistent and ineffective way to stay on top of proper watering of trees, shrubs, and perennials. One of the questions Glacier View Landscape gets asked most often is, “How and when should I water?”. It is a multifaceted question to answer, but in this short article I’ll attempt to address a few of the most common misconceptions and best techniques I’ve found over the last 29 years in Colorado for keeping outdoor plants thriving.

First and foremost, we need to determine if the watering we are doing will be with an automated irrigation system or if one is watering by hand. In Colorado, if you have more than a “patio” garden, you will probably save yourself a lot of time, money and agony (due to plant replacements) if you have an automated irrigation system to help with watering. The reason I use the term “help” is that an automatic system, even if set up by a professional, is not foolproof. I’ll discuss that later. Watering by hand with a hose and watering wand or sprinkler is time consuming. It is also inefficient since some areas will end up overwatered and other areas will be underwatered. But, for the sake of comparison, let’s assume you are watering both plants and lawn with hose and watering wand and sprinkler. In general, if there has been no rain and it is the middle of summer, most established small deciduous trees need about 7 gallons of water for every one inch of diameter of trunk (called caliper if measured 8” above the ground) per week. So, if you have a 2” caliper tree that has been in the ground for more than 1 year, it will need 14 gallons of water per week. This is a general rule of thumb as soil type, soil compaction, and exposure to wind and sun will greatly affect the amount of water needed. Trees in exposed, windy and bright sun conditions, like those found on new construction sites, may need twice this amount or more. In general, trees should not be watered until the surface soil has dried sufficiently to allow air to penetrate the soil into the root zone. Plants need air as well as water to establish healthy root systems. Also, on established trees, the root zone will extend as far as three times past the diameter of the drip zone (the area under the canopy of the tree) depending on species and soil conditions. Therefore, do not water near the trunk on established trees as this can lead to disease, but instead, water only in the root zone. This is true for established shrubs as well, though it will not kill the shrub to water inside the drip zone. Also, moisture is better conserved under the shade of the tree and shrubs than it is in areas outside the drip zone. When I water by hand (I have a drip system but sometimes supplement watering during very dry and hot periods), I make sure to soak the plant stems and leaves and let the water drip into the shrub root zone under the shrub or tree. I also make sure to let water run outside the area that is shaded by the plant where the newest roots are attempting to grow. In essence, I try to imitate what a good steady rain shower would accomplish for my plants. For lawns, watering by hand is a huge pain and usually a waste of water if the lawn is to survive the heat of summer. Homeowners usually end up “chasing dry spots” a lot in order to keep areas from turning brown. In general, lawns in Colorado need around 1” of water per week to survive. I could write a whole Ph.D. dissertation on lawn care, but for this article, I’ll keep it short. Many homeowners along the Front Range of Colorado however, do not ever water by hand. Instead, they rely on an automated irrigation system.

Drip systems and automatic irrigation systems are not inexpensive to install, but over time, their benefits far outweigh the initial cost of installation if done properly. I would estimate that more than ½ of all automatic irrigation systems I see either waste more water than they save, or are ineffective in maintaining the correct soil moisture on a property. As well, I see too many homeowners who do not know how to properly program their irrigation systems, nor adjust them as necessary as the season progresses….they just set them in the spring and leave them until the fall/winter shutoff period. This wastes water in the spring and fall and usually underwaters plant material during the heat of summer when plants and lawns need water most. On good irrigation timers, there is something called “seasonal adjustment” which allows one to set the watering times for all zones programmed based on a percentage. So, in spring and fall, the percentage watered might be 75% and in summer, it might be 125% of the programmed time for all zones. Also, how often does one see sprinklers running while it is pouring rain? More often than should be. Many irrigation suppliers now offer precipitation monitoring systems (rain gauges or internet connections to automated meteorological stations that collect information on rainfall) which automatically shut off a system when a preset threshold of rainfall has been recorded. Most residential applications do not have this, so it is up to the homeowner to be cognizant of rainfall at their home. If we get a small, short lived summer thunderstorm, it probably didn’t wet the soil much….stick a finger or a sick in the ground next to a plant to see if it is wet. If dry a ½ inch down, leave the system on. However, if we get a ½ inch of rain a day for 3 days, this moisture soaks in well and the system should be turned off for a few days. Some systems allow one to program in a 48 or 72 hour delay so that one does not have to remember to turn the system back on. If not, don’t forget to turn it back on!

When Glacier View Landscape sets up an irrigation system, we use drip emitters (the small plugs that let water out at the base of each plant) that have a specified flow rate. For example, we use mostly 2 gallon per hour (gph) emitters. Therefore, we regulate water to each plant based on its need by how many emitters are placed at the base of the plant. Then, the entire zone will run for a set time per week to deliver the amount of water needed. This is where science and math come into play. Plants, when first installed need more water than they do if they have been in the ground for a few years. So, for the first growing season, Glacier View might program a system to deliver 6 gallons of water per week to a shrub. But after a year or two, this can be dialed back to 4 gallons of water per week. However, as the plants get much bigger, they need more water, and the system will need to be adjusted again to deliver perhaps 8 gallons of water per week to that shrub. When plants are first installed, there is a very fine line between watering properly and overwatering or underwatering. As was described earlier, plants need air and water to survive. The water, for example, cannot be delivered to trees and shrubs every day or multiple times per day since the soil surface will remain saturated, thus not giving the rootball of the new shrub a chance to breathe. Instead, we program our system to deliver water 2 or 3 times per week for a set time, so that over the course of a week, they get the water needed. In the summer months, as little as 150% of the needed water can kill new plants if not administered properly (i.e. running a drip system 3 times a day for 7 minutes instead of three times a week for 30 minutes). So, in general, it is better to water with more water less frequently than to water more frequently with less water. The water needs to soak in but still give the rootball a chance to dry out some between watering. For lawns, there are five rules of thumb Glacier View adheres to. First, double cover all areas. This means that one sprinkler head will cover an area that reaches to all adjacent sprinkler heads. Second, zones are installed to cover areas with similar exposures (sun and wind). This allows adjustment of the zone so that less water is given to areas that are shaded more, and more water to areas that are exposed to more sun and wind. Third, all heads are specifically adjusted and nozzles are properly chosen. This means that the proper amount of water is coming out of each head (remember gallons per hour (gph) for drip systems?….the same (gph) can be adjusted for all sprinkler heads), and that the water is not overspraying sidewalks or planted beds (plants cannot handle the amount of water put on lawns…they will drown). Fourth, the correct type and size of sprinkler head is chosen for the application (usually a popup type head versus a gear driven head). And finally, fifth, the amount of water applied to the turf must be appropriate to maintain a green lawn without runoff. Newly sodded lawns require 3 times the amount of water of an established lawn for the first 3 weeks after installation. New sod must remain wet until roots are established. However, with proper soil preparation, a newly sodded lawn by Glacier View Landscape will use less water over time. For example, microscopic Kentucky Bluegrass roots will extend down 18” or more in properly prepared soil, thus making bluegrass quite drought tolerant in the worst of conditions. In my experience, when these 5 things are adhered to, water usage on turf areas can be reduced by as much as 30% or more.

Let’s not forget winter watering as well. It is as important to maintaining a healthy landscape as watering in the summer. The general rule of thumb I use is as follows: If there has not been snow on the ground under or around a particular tree or shrub on your property for three weeks, it needs water. I phrase it this way because a tree on a berm exposed to sunlight will be snowfree with non frozen soil far sooner than a shaded area on the north side of a fence. Water 10 gallons for every 1” of trunk diameter for trees throughout the root zone. For shrubs, the amount of water varies greatly due to size, but, on average, for every 1’ of height, water with 3 gallons of water. For evergreen trees, water 1 gallon for every 1’ of height. Do not water when the ground is frozen. And, only water then the temperature is above 45 degrees. Well established trees need little additional water except in the driest of winters. However, it takes a long time and a lot of water to soak the roots of a 60 foot Oak. These suggestions are mostly for younger, less mature plant material. Your experience with your own property will dictate your winter watering schedule.

Water conservation is an important part of landscape design and installation, especially in dry and drought prone areas such as the Front Range of Colorado. Proper watering of plants and lawns can provide a lush looking landscape while still using less water than a more sparse looking landscape with an inefficient irrigation system. This article is, by no means, comprehensive. Instead, it is meant to get the homeowner thinking about the complexities that go into proper planning of an efficient irrigations system and to provide a few tips on proper watering techniques. Hopefully, these few tips have answered some of the questions concerning irrigation on your property. For a complete analysis, let a professional come to your property to help you save as much water as possible yet still maintain the lush landscape you desire.

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