Autumn temperatures have cooled and winter lows are just around the corner. As the air and soil become chilly, most plants slow down their development and need only enough moisture to prevent dehydration. It is time to again discuss winter watering for landscape plants and trees.
This is the season to reset automatic timers if a drip irrigation system is being used. It is important to reduce the frequency that water comes on; however, leave the duration of each watering cycle unchanged.
It is recommended that most established dormant trees and shrubs now be watered every 2 to 3 weeks. This is also true for citrus trees. Perennial plants and groundcovers prefer water every 10 to 14 days. Rainfall must also be considered as part of a water management program.
Using a soil probe or length of rebar, measure the depth of moisture. Water small plants to a depth of 12 inches. Medium-size plants such as shrubs should be watered to a depth of 24 inches. Trees generally should be watered to a depth of 36 inches.
Approximately an hour after watering, push the probe or rebar into the soil close to the plant in question. It will easily slide through wet soil but become difficult or impossible to push through if dry. Pull out the probe or rebar and measure how deeply it went down. This shows how far down the water has moved; if not deep enough, continue adding water until the probe can easily reach the desired depth.
Soil texture will vary from one location in your landscape to another. There may be patches of sand where water quickly disappears. Heavy clay deposits can easily become waterlogged. Layers of hardpan, also called caliche, can totally stop drainage. Our soil also contains many stones which interfere with pushing the probe into the soil without multiple trials.
A good gardener becomes acquainted with his or her various soil types and how each handles water. This can be a huge challenge because of the many components of soil, each with its own drainage characteristics.
University of Arizona/Pima County Extension Service has advised to not water cactus growing in the ground during winter. Rot potential is greatly increased when roots are too moist during cool weather. Cactus in containers should be watered just enough to keep the soil from totally drying out.
Potted plants, although requiring more frequent water, are also quite susceptible to rot, so take care to not overwater them. Check soil with a commercially available moisture meter or the old-fashioned “damp-soil-on-the-finger” test.
Keep in mind that landscape plants require 3 to 5 times less water in winter than during our summers. To determine the best water management plan for your landscape, inspect your plants regularly. As said long ago, “The best garden plans come from the gardener’s shadow.”
Mary Kidnocker is a University of Arizona Master Gardener who lives in the Green Valley area. Her articles are featured weekly.