Knowing How Much to Water, Part II: #itsSTILLcomplicated
Southwest Yard & Garden
by Dr. Marisa Thompson
Question:
How much should I be watering my trees?
- Multiple
Gardeners from All Over NM
Answer (Part 2):
In last week’s column,
we learned about how the type of soil in your garden affects tree water
requirements. Now we will focus on other considerations, such as rates of water
movement, tree species, age, canopy size, and seasonal fluctuations in water
needs.
Plants
take water up from the soil through their roots all the way to the leaves where
it is released into the air. Transpiration is the process by which a plant
loses water, primarily through pores in the leaves called stomata. This is a
necessary process that involves the use of about 90% of the water that enters
the plant through the roots. The other 10% of the water is used in chemical
reactions, like photosynthesis, and in plant tissues. Transpiration is
necessary for mineral transport from the soil to the plant tissues, for the
cooling of the plant through evaporation, for moving sugars and plant
chemicals, and for the maintenance of turgor pressure. The amount of water lost
from the plant depends on several environmental factors such as temperature,
humidity, and wind or air movement.
Here's a video I found on YouTube that provides a helpful visual of transpiration in action. PLEASE NOTE: the cartoon depiction of the tree roots in this video are NOT accurately drawn!
Here's a video I found on YouTube that provides a helpful visual of transpiration in action. PLEASE NOTE: the cartoon depiction of the tree roots in this video are NOT accurately drawn!
Mary Irish and Judith Phillips include a simple table on how much and how often
to water landscape plants in their book, “Arizona & New Mexico Getting
Started Garden Guide.” In this table, trees in New Mexico are divided into two
categories: cool desert-adapted and high water use. The recommended number of
days between waterings differ depending on the time of year, partly because
tree water needs increase when temperatures are higher. In winter they
recommend watering established, cool desert-adapted tree species once every
45-60 days. Intervals of 14-30 days between waterings are suggested in the
spring and fall and shorter intervals of every 7-21 days in the summer. More
water may be needed for trees that are newly planted (less than three years),
especially in the hottest, driest times of the year.
Slow
soaks at long intervals between irrigation events are best for tree root
systems. Remember that for mature, happy trees the hard-working,
actively-absorbing root hairs are more concentrated in the top two feet of soil
depth and extend out beyond the canopy, even two to four times the height of
the tree. So be sure to water deeply enough and not just at the base of the
tree trunk. For younger or neglected trees, it is most important to apply water
both where you know where the roots are and where you want them to grow.
Irrigation scheduling table from "Arizona & New Mexico Getting Started Garden Guide" by Mary Irish and Judith Phillips, page 225. |
Drip
irrigation is a great method for watering trees as long as enough water is
applied to really soak down into the soil and the placement of emitters will
need to be modified each year to accommodate root and canopy growth until the
trees are established. Similarly, low berms of soil can be used to build a
basin around the dripline of a young tree if watering with a hose, but these
too will need to be expanded as the tree grows.
Certainly,
some plant species are bigger water guzzlers than others. Several
municipalities offer lists of recommended trees and other plants for their
specific climates. If you know of a reference you think might
be useful for others please share it with me via on social media (@NMDesertBlooms).
Shade Trees for New Mexico NMSU Extension Publication Guide H-326
Selecting Ornamental Trees for New Mexico NMSU Extension Publication Guide H-328
Fruits and Nuts for New Mexico Orchards NMSU Extension Publication Guide H-310
NMSU offers a wide selection of other helpful publications. Check them out here: http://aces.nmsu.edu/pubs/
Several counties offer lists of recommended trees and other plants for their specific climates. If you know of another reference you think might be useful please share it in the comments section below (or on social media!).
More and more communities in New Mexico are adopting incentives for water-wise gardening, like rebates (aka “tree-bates”) for the inclusion of low water use plant species and installation of drip irrigation systems with controllers (https://www.abcwua.org/Xeriscape.aspx).
The Albuquerque Bernalillo County Water Utility Authority
printed this great
handout as a guide for converting to a water-wise
gardening strategy and getting
rebates on your water bill!
|
It is tricky to figure out when to water, how much, and how to deliver water to the trees in your garden. Try not to get discouraged. Selection of species that grow well in our climate with minimal extra water is an excellent first step. Mulches and groundcovers are also great tools for conserving soil moisture so that less water is evaporated directly from the soil into the air, but I will save those topics for another week.
Send
gardening questions to Southwest Yard and Garden -
Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu,
or at the Desert
Blooms Facebook page (@NMDesertBlooms)
Please
copy your County
Extension Agent and indicate your county of residence when you
submit your question!
Edible New Mexico Magazine article crosslink -- GROWING YOUR FUTURE FAVORITE TREE
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