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How Much Does it Cost to Water This Tree?

Emily Hanson — Sat, 04 Apr 2009 12:06:48 +0000

View as a PDF: How Much Does it Cost to Water this Tree?

By: Adam Flett, Department of Forest Resources Extension and Outreach, University of Minnesota Technical Advisors: Gary Johnson, Department of Forest Resources and John Lamb, Department of Soil, Water and Climate

Water is a biological necessity for all trees, whether in a landscape or woodland setting and must be available over an entire growing season (June through October). Healthy trees are the result of efficient watering; not supplying so much that the roots die from lack of oxygen or too little makes all the difference.

Whether the water source is rain, a well or a local utility, there is often a need for water “budgeting” for economic and ecological reasons. This fact sheet will help determine the maximum amount of irrigation water per dose (amount of water needed at each irrigation) for three different tree sizes. A number of variables affect the amount needed, but the calculations provided represent a situation where water is assumed purchased and one dose is applied per week from the beginning of June to the end of October. This is an unlikely event in Minnesota, but presents a perfect “worst-case” scenario for water costs.

The lives of three trees

Three specific tree life stages will be used as common examples. The first is a newly planted tree with a 2” trunk caliper (caliper is the width or thickness of the trunk measured 6-12 inches above ground). The second is an established tree with a 10” DBH (DBH is Diameter at Breast Height, measured roughly 4.5 feet above the base of the trunk). The third stage is a mature tree with a 30” DBH.

This factsheet uses a “worst-case” assumption. Soils are assumed to be sandy-loams that are well drained with no groundcover. A dose means filling a volume of soil to field capacity to an 8” depth (field capacity is the most water a soil can hold) and sandy-loam soils have the ability to hold the greatest amount of water. This “worst-case” also assumes that by the end of one week, the soil contain no available water for the trees to use (permanent wilting point).

How much water is needed, and at what cost?

Newly Planted Trees
As suggested by Gilman, Black, and Deghan (1998), newly planted trees need about 1-1.5 gallons of water per caliper inch of trunk diameter. For example:

2” Caliper x 1.5 gal. /inch = 3 gallons per dose (2 cents per irrigation)

Established and Mature Trees
The critical root area (the root area that takes up most of the water) is calculated by using a ratio of inches at DBH to feet of root radius, where one inch in DBH accounts for 1.5 feet of critical root radius from the trunk base. The calculations for 10” and 30”DBH established trees are:

Established: 10” DBH x 1.5 feet per inch DBH= Radius (r) = 15 foot radius

Mature: 30” DBH x 1.5 feet per inch DBH= Radius (r) = 45 foot radius

Extending from the base of the tree, the radius should account for most of a tree’s root surface area.

Volume of Soil to be Watered
Calculating the volume of soil to be watered will require a little bit of math, the radius identified above and the following equation for calculating the volume of a cylinder.

Volume of a Cylinder: 3.14 x (r) 2 x Height (h)

Fig.1: Diagram of Volume of Soil

Height was established as 8” depth (or two thirds of a foot). The calculations for volume of soil are only necessary for the established and mature trees. They are:

Established: 3.14 x (15’) 2 x 8” = 474 ft3
12”

Mature: 3.14 x (15’) 2 x 8” = 4241 ft3
12”

Amount of Water Needed per Dose
Determining the amount of water needed to fill the volume of soil is the next step. The ratio is based upon the amount of water required to bring a sandy loam soil from permanent wilting point (no available water in the soil) to field capacity. This will equal one dose. Calculations will require three steps. First, calculate the percentage of water needed to fill a sandy-loam to field capacity. This includes a constant supplied by Jeff Ball (2001) on Soil and Water Relationships. The constant is given in inches of water per foot of soil depth; sandy loam is given a range of 1.25-1.40 inches/foot of depth. For the purposes of this factsheet we will use the higher value, and 1 foot will be considered 12”. The calculation is as follows:

Percent Volume (Pv) x 12” depth = 1.40 inches/foot

PV = 1.40/12”

PV = .1167 or 11.67%

∆ What does this mean?
The PV number (11.67%) shows the percentage of the soil volume in part B that can be filled with water (to field capacity). Using the values calculated in part B and the percentage above, the cubic feet of water needed to reach field capacity can now be calculated:

Established Tree: 474 ft3 x .1167 = 55 ft3of water (55.3 exactly)

Mature Trees: 4241 ft3 x .1167 = 495 ft3of water (494.9 exactly)

A spigot with an attached flow meter shows flow rates in gallons. If this is the case, use the ratio of gallons to cubic feet of water, where there are 7.48 gallons per cubic foot of water.

Total Seasonal Water Cost
Finally, calculate the total amount of gallons used and the relative costs (City of St. Paul Water and Sewage Rates 2009). The rate is the sum of water consumption charges and sewage rates June 1st through October. This assumes that all water entering the system (consumed) leaves as sewage (the most expensive way to buy water). Multiply the total cubic feet per dose by the number of weeks and by the summed rates ($5.28/100 ft3):

Established Tree: 55 ft3 x 21 weeks X $5.28/100 ft3 = $61 per season ($60.98 exactly), OR $2.95 per dose

Mature Tree: 495 ft3 x 21 weeks X $5.28/100 ft3 = $549 per season ($548.86 exactly), OR $26.14 per dose

Reducing the amount and cost of water

Exposure to wind and/or sun greatly affects the soil’s ability to hold water over a weeklong period. If a tree is in a windy or sunny location, it loses water more quickly, whereas if it is shaded or sheltered one dose every week and a half to two weeks may be sufficient.
Different soils can drastically change the gallons per dose. Trees growing in sandy soils will most likely require more frequent watering due to lower water retention capacity. Trees growing in silty and clayey soils require less frequent irrigations because those soils tend to retain water longer.
The tree type may also affect the frequency of irrigation. Trees that tend to grow in moist soils will require more frequent watering. Trees that grow in dry environments tend to survive without water for longer periods of time and require less water.
Competitive groundcovers such as turf grasses significantly increase the amount of irrigation water necessary for healthy trees. Even weeds can lead to increased evaporative water loss by as much as 25% on a hot, sunny, summer day. If no groundcover is present there is no competition and all water is available for the tree (or evaporation). An organic ground cover of any sort (such as woodchips) will help retain water for the tree, reduce evaporation and decrease the frequency of irrigation. According to at least one experiment, when compared to bare soil a relatively thin layer of organic mulch (1.5 inches) reduced water loss due to evaporation by as much as 35% (Chalker-Scott, 2007).

Watering options

Water bags: Water-filled bags are placed around the trunk of the tree and drip water to the immediate root area at the base of the tree over a few hours. This allows water to be absorbed by the tree rather than running off.
Soaker Hose/Drip irrigation: Cut slits or poke holes into a hose to allow water to seep into ground rather than spraying (which loses water through evaporation). Keep flow rate low to allow for seeping. Or, buy soaker hoses.
Water tape: a flat, hose like device, water tape is highly efficient for irrigation. It seeps at a very low rate, only at points of perforations, and is commonly used in nursery operations.
Sprinklers: the least desirable due to high rates of evaporation and low efficiency ratings.
Water gauges: there are many water gauges available, ranging from less than $40 to more than $500, and measure the exact amount of irrigation water per dose regardless of flow rates or watering equipment.

Funding for the research and production of this article was provided by the University of Minnesota Extension Service, Department of Forest Resources, and the RREA.

Referenced Reading: Ball, Jeff. 2001. Soil and Water Relationships. Ag News and Views Soils: September 2001. Online. 23 Jan. 2009. www.medicagotruncatula.org/Ag/Soils/SoilWaterRelationships ; City of St. Paul. 2009. Water Rates. On-line. 12 Feb. 2009. http://mn-stpaul.civicplus.com/DocumentView.asp?DID=3493 ; Chalker-Scott, Linda. 2007. Impacts of Mulches on Landscape Plants and the Environment – A Review. Journal of Environmental Horticulture 25(4): 239-249 ; Gilman et. Al. 1998. Irrigation Volume and Frequency and Tree Size Affect Establishment Rate. Journal of Arboriculture 24(1): 1-9

Recommended Trees for Minnesota by Region

Emily Hanson — Mon, 17 Nov 2008 20:29:36 +0000

Trees shade and cool us in the summer, protect us from cold winter winds, supply us with clean air to breathe, beautify our communities and provide habitat for wildlife. Selecting the trees that will survive and grow into healthy urban forests requires a thorough analysis of the planting site and a careful match of the trees to that environment.

The Recommended Trees series recognizes that Minnesota is an ecologically diverse state. For this series, the state is divided into six major ecological regions, each with characteristic soils, precipitation patterns, topography, and natural vegetation. Recommended trees for each region perform reliably in that environment, and should thrive for many years.

The following links recommend which trees should be selected for each region of Minnesota:

Selecting woody and herbaceous plants for landscapes and roads

Emily Hanson — Mon, 17 Nov 2008 19:21:24 +0000

Making Choices for Roadside Planting

The Minnesota Department of Transportation’s Plant Selector program, Woody & Herbaceous plants for Minnesota Landscapes & Roadsides, was developed in 1995 and through several phases has been refined to become more user-friendly. The primary goal and objective of this program is to facilitate selecting the most appropriate plants for landscaping on Minnesota Roadsides or Landscapes. Picking plants for roadside planting in Minnesota can be a problematic task considering the constraints within Minnesota.

Click to use PlantSelector

Woody biomass: Sept. 2009 bio-baler demonstrations

Seasonal Care for Trees and Shrubs in Northern U.S. Climates

Rebecca Koetter — Sun, 06 Apr 2008 11:06:23 +0000

Welcome to the world of tree care! In the left hand column of the image below, you will find links to the many maintenance duties you can do to help keep your landscape trees healthy and safe. The accompanying chart highlights the most favorable timing for the listed tree care activities. Below this chart you can find links to other complete chart versions that are larger and easier to read.

Overall, periods of weather extremes (e.g., drought or high winds) should be avoided when planting, transplanting, fertilizing and pruning. The information available in this website provides a place to start for tree and shrub care, is not absolute for every situation, and is not intended to endorse any products or services.

Have fun!

More information on each step:

Authored by Rebecca Koetter, Gary R. Johnson, and Dave Hanson: University of Minnesota
Funded in part by USDA Forest Service: Northeastern Area
Chart designed by Andrew Rose: www.handeye.us

Download & print your own poster or magnet copy of the “Seasonal Care for Trees and Shrubs in Northern U.S. Climates”

Poster: 8.5″ x 11″ size (.pdf) – 408 KB
Poster: 22″ x 28″ size (.pdf) – 16.77 MB – VERY LARGE!
Magnet: 4″ x 7″ size (.pdf) – 560 KB

Seasonal care for trees & shrubs: Safety

Rebecca Koetter — Fri, 04 Apr 2008 17:49:15 +0000

Inspect your landscape trees and shrubs often- especially after storms. After storms, hazard trees with loosely hanging branches or split trunks need to be removed as soon as possible to avoid any damage to buildings, people, and to other trees or shrubs.

At other times of the year keep a watchful eye for developing decay in trunks and roots, broken and hanging branches, dead branches or trees, an abnormally leaning tree, or anything that may indicate that a tree or part of it could fail and cause damage or injury.

Certified Arborists can offer advice on which plants should be removed, which ones can be saved, and if Plant Health Care (PHC) treatments are necessary. Visit the International Society of Arboriculture (ISA) website to find a Certified Arborist nearest you.

For more information : How to Recognize Hazardous Defects in Trees and Hazard Tree Prevention

More information on each step:

Authored by Rebecca Koetter, Gary R. Johnson, and Dave Hanson: University of Minnesota
Funded in part by USDA Forest Service: Northeastern Area
Chart designed by Andrew Rose: www.handeye.us

Download & print your own poster or magnet copy of the “Seasonal Care for Trees and Shrubs in Northern U.S. Climates”

Poster: 8.5″ x 11″ size (.pdf) – 408 KB
Poster: 22″ x 28″ size (.pdf) – 16.77 MB – VERY LARGE!
Magnet: 4″ x 7″ size (.pdf) – 560 KB

Seasonal care for trees & shrubs: Health

Rebecca Koetter — Fri, 04 Apr 2008 17:49:11 +0000

Keep a watchful eye for problems that may be developing on the plants in your landscape. Timely prevention is always more effective and economical than reacting to problems once they have developed. Certain samples can be sent to your local Plant Disease Clinic (.pdf) for diagnosis.

For more information : Diagnosing Tree Health Problems (.pdf) and Forest and Shade Tree Health

If damages are observed and if Plant Health Care (PHC) treatments are necessary, contact a local Certified Arborist for an on-site diagnosis. Certified Arborist’s in your area can be found through the International Society of Arboriculture (ISA) search engine.

More information on each step:

Authored by Rebecca Koetter, Gary R. Johnson, and Dave Hanson: University of Minnesota
Funded in part by USDA Forest Service: Northeastern Area
Chart designed by Andrew Rose: www.handeye.us

Download & print your own poster or magnet copy of the “Seasonal Care for Trees and Shrubs in Northern U.S. Climates”

Poster: 8.5″ x 11″ size (.pdf) – 408 KB
Poster: 22″ x 28″ size (.pdf) – 16.77 MB – VERY LARGE!
Magnet: 4″ x 7″ size (.pdf) – 560 KB

Seasonal care of trees & shrubs: Stem and branch protection

Rebecca Koetter — Fri, 04 Apr 2008 12:59:53 +0000

Stem Protection

The stems of landscape trees and shrubs may need protection from animals or mechanical equipment, especially during the winter months. Animal damage (feeding or rubbing) can be avoided by placing wire mesh or hardware cloth at least 3” from the stem. Mechanical damage (e.g. lawn mower or weed whip abrasion) can be avoided when a mulch ring (see mulch) or a plastic guard is in place. The plastic guard should only encase the portion of the lower stem that is most likely to be damaged by lawn equipment. As the tree grows the plastic guard will need to be removed and replaced in order to prevent girdling or stem constriction.

Branch and Foliage Protection

Ice and snow loading damage can be severe during cold, wet winters on multi-stemmed evergreen trees and shrubs (e.g. junipers, arborvitae, and yews). The overall form of the plant can be protected when the branches are secured with twine or burlap. Read page 3 of the below publication for more information. In order for the tree to resume normal growth remove the twine or burlap by spring.

For more information: Protecting Trees and Shrubs from the Wicked Winters of the Upper Midwest (.pdf).

More information on each step:

Authored by Rebecca Koetter, Gary R. Johnson, and Dave Hanson: University of Minnesota
Funded in part by USDA Forest Service: Northeastern Area
Chart designed by Andrew Rose: www.handeye.us

Download & print your own poster or magnet copy of the “Seasonal Care for Trees and Shrubs in Northern U.S. Climates”

Poster: 8.5″ x 11″ size (.pdf) – 408 KB
Poster: 22″ x 28″ size (.pdf) – 16.77 MB – VERY LARGE!
Magnet: 4″ x 7″ size (.pdf) – 560 KB

Seasonal care of trees & shrubs: Fertilizing

Rebecca Koetter — Fri, 04 Apr 2008 12:46:33 +0000

From an environmental quality and tree health perspective, all fertilizing of trees is recommended only in a case-by-case situation in the landscape. Fertilizing is not recommended unless nutrients are proven deficient in a soil sample tested by a laboratory or by a trained eye observing a deficiency in a plant’s foliage.

The recommendations in this chart refer only to nitrogen applications. Before fertilizing your landscape with a complete fertilizer (nitrogen-phosphorus-potassium), contact a soil testing laboratory for a basic soil test [For MN only: U of MN Soil Testing Labratory]. A basic soil test will provide you with readings on organic matter, pH, cation exchange capacity, macronutrients and micronutrients (Smiley, 2003). Soil testing laboratories may offer timing and quantity recommendations for complete fertilizers (N-P-K).

For information on selecting a soils lab for testing visit Guidelines for Choosing a Soil-Testing Labratory. Once criteria have been determined for selecting an appropriate soil lab, visit University Related Plant Disease and Soil Testing Services (.pdf) to find the lab nearest you.

Nitrogen needs are not usually highlighted on soils test. Standard soil tests do not include total nitrogen readings since nitrogen is present in so many forms and is so mobile. According Dr. Kim Coder, adding (aka. “dumping”) too much nitrogen at one time can increase the plant’s susceptibility to insects and diseases, decrease drought tolerance, and can pollute waterways (1997). It has been determined that high nitrogen use efficiency is achieved when trees are leafed out.

Application rate is critical: NEVER exceed package recommendations. Do not apply on hot, dry and/or frozen soils. Avoid nitrogen applications from leaf drop to bud break because uptake is minimal and pollution may occur.

For more information : Tree Nutrition Series: Nitrogen Perscription for Trees

More information on each step:

Authored by Rebecca Koetter, Gary R. Johnson, and Dave Hanson: University of Minnesota
Funded in part by USDA Forest Service: Northeastern Area
Chart designed by Andrew Rose: www.handeye.us

Download & print your own poster or magnet copy of the “Seasonal Care for Trees and Shrubs in Northern U.S. Climates”

Poster: 8.5″ x 11″ size (.pdf) – 408 KB
Poster: 22″ x 28″ size (.pdf) – 16.77 MB – VERY LARGE!
Magnet: 4″ x 7″ size (.pdf) – 560 KB

Seasonal care for trees & shrubs: Staking or guying

Rebecca Koetter — Fri, 04 Apr 2008 12:42:32 +0000

Staking and guying of trees is rarely needed and is only necessary when the tree will not stand up on its own. These practices may be necessary for 1-3 years while roots are growing and beginning to stabilize the tree. Check attachment points on the stem every 3 to 6 months, loosen if necessary and remove within one year of placement.

For more information : Staking and Guying Trees: Best Materials and Techniques

More information on each step:

Authored by Rebecca Koetter, Gary R. Johnson, and Dave Hanson: University of Minnesota
Funded in part by USDA Forest Service: Northeastern Area
Chart designed by Andrew Rose: www.handeye.us

Download & print your own poster or magnet copy of the “Seasonal Care for Trees and Shrubs in Northern U.S. Climates”

Poster: 8.5″ x 11″ size (.pdf) – 408 KB
Poster: 22″ x 28″ size (.pdf) – 16.77 MB – VERY LARGE!
Magnet: 4″ x 7″ size (.pdf) – 560 KB