• Transpiration starts at the
• Capillary action pulls water from
• Soil moisture is depleted.
• Hot, dry air increases
• Wind blowing across leaves
Tree’s response to drought:
• Stomata close and photosynthesis slows.
• Death of root hairs and feeder roots
• Wilting, scorch, and defoliation
• New leaves may be smaller than normal.
• Premature fall color
• Dieback of shoots
• Growth in height and girth declines.
• Heavier than normal seed production
• Increased susceptibility to insect pests
(spider mites, wood-boring insects)
• 4,850 square feet
• 15% hardscape
• 45% turf
• 15% shrubs
• 21% perennial beds
• 5% ground cover plants
• 12 trees
• Irrigated by pop-up sprinklers
Average annual water use =
Rosenberg et al., 2010,Value Landscape Engineering: Identifying costs, water use,
labor, and impacts to support landscape choice, Journal of the AmericanWater
• 4,870 square feet
• 20% hardscape
• 0% turf
• 60% shrub beds
• 20% perennial beds
• 0% ground cover plants
• 18 trees
• Irrigated entirely by drip
Average annual water use =
Trees are the most valuable asset in our urban areas.
Goal of irrigation
Replace the water lost from
the root zone due to:
•Percolation below the
• Up to 90 percent of the total root system length is
accounted for by fine, absorbing roots.
Fine, absorbing roots
•Group plants with
similar water needs
•Irrigate zones on
Two aspects to irrigation scheduling
How much water to apply…
How often to apply it.
Water trees deeply
Watering depth for different plants:
18 to 24 inches
12 to 18 inches
Herbaceous plant roots
6 to 12 inches
6 to 8 inches
Calculate estimated daily water use
Gallons per plant =
0.623 x plant area x plant factor x reference
evapotranspiration (ETo) per day ÷ irrigation
Based on ASCE guidelines and modified for practical use.
= Crown diameter2 x 0.7854
Crown diameter = 10 ft., so 102 (10 x 10) x 0.7854 = 78.54 sq. ft.
Plant factor for trees ranges from 0.5 to 0.8
Reference water loss (ETo)
ETo: 4 -6” fescue turf,
Water trees less frequently
GALLONS OF WATER PER WEEK
Plant canopy diameter in feet
1 2 3 4 5 6 8 10 12 14
Information valid for western Nevada and other similar climates during summer.
•Measured in GPH rather
•Less loss to evaporation
•Reduces runoff and
•System efficiency of 80%
to 90% (sprinklers < 75%)
Micro-irrigation emission devices
(low pressure 10-30 psi)
• Drip emitters – for shrubs and small trees (0.5–6 gph)
• Bubblers – best for new trees with a berm or trees in wells (2–20 gph)
• Micro-spray emitters – for medium to large trees (3–30 gph)
The main difference is the mode of water dispersal.
• External emitters connected
to the lateral distribution line
using spaghetti tubing
• Fewer heads needed
to cover large areas.
• Visible to easily check for
Example: How long should I water?
Size Drip Emitters Microspray Emitters
20 2-gph emitters for
4 hours once a week
Eight 20-gph emitters
for 1 hour once a week
14 2-gph emitters for
3 to 4 hours once a
Six 14-gph emitters
for 1 to 1.5 hours once
10 2-gph emitters for
1.5 to 2.5 hours once a
Five 11-gph emitters
for 0.5 to 1 hour once a
Based on gallons of water needed per tree.
The spread of the wetting front depends on soil texture.
Emitter arrangement for young trees
• Wet as much of the root ball as
• Irrigation line should not be up
against the trunk.
• Emitters should be placed within
and beyond the spread of the root
ball to encourage root growth into
Roots don’t seek water – they follow water.
Result of inadequate early water distribution
Roots won’t spread into dry soil.
Emitter arrangement for mature trees
New Mexico State University
The depth and distribution of water application will determine the architecture of the root system.
How will the architecture of this tree’s
root system look?
Other strategies for managing trees
• Mulch at least out to the drip
line, further if possible.
• Do not fertilize trees during
• Limit pruning to removal of
dead wood or crossing
Water is lost through leaf stomata (pores).
What our eyes see What our eyes can’t see
Plant adaptations to arid conditions
• Leaf size
• Leaf color
• Leaf orientation
• Extensive root system
Rocky Mountain Juniper
Common Hackberry Gambel OakFremont barberry
Some species susceptible to secondary infestation
by bark beetles and borers
Many native trees are not drought-tolerant:
Ponderosa pine in an urban area
Trees that do surprisingly well with less water
(in zones 4 – 7)
• Coffeetree, Kentucky
• Corktree, Amur
• Cyprus, Leyland
• Hackberry: Common, Douglas,
• Hawthorn: Cockspur, Green,
• Juniper, Rocky Mountain
• Maple: Amur, Sycamore,Tatarian,
• Mulberry: Red, White
• Oak: Bur, Chinkapin, Gambel,
• Pine: Bristlecone, Jeffrey, Limber,
• Sycamore, American
• Zelkova, Japanese
University of Nevada Cooperative Extension
This presentation was brought to you by the Nevada Extension IPM Program and funded by USDA-NIFA.