Given that we all have twenty digits; I will point out which ones to use to see if your trees and shrubs are in need of water. Most people wear shoes or boots in the garden eliminating ten digits. As you may have guessed the most cost effective digital moisture meter is your index finger.
Stick it in the ground and if it feels moist and cool you don’t need more moisture. If the ground feels hard and dry, even dusty as you stick your finger in the soil it’s time to water!
It really is that simple and you will never have to buy batteries.
Trees and shrubs need ample, timely water to thrive. Plants need a certain minimum amount just to survive. Soil moisture normally constitutes 1/3 of the volume of soil; the remaining two thirds are occupied by the soil particles and air. Depending on the composition of the soil a varied amount of the water in the soil is available to the plants. Some water will be bound so tightly to the soil particles that it will be unavailable for plants. Water that isn’t bound to soil particles is said to be available soil water and this is what trees and shrubs can use.
Plants use water in a wide variety of plant processes including transporting nutrients and minerals throughout the plant. The greatest percentage of the water in most plants is used to cool the plant. Trees and shrubs cool them selves by allowing moisture to evaporate from leaf surfaces. This process is called evapotranspiration. Essentially evaporation and transpiration combined. Cells in the roots passively gather water through osmosis; they soak it up like paper towel, or a dry sponge. The water is then transported upward in the plants cells some times actively like a bucket brigade, or passively from cell to cell by osmosis. As it gets to the top of the plant it is exposed to the air and evaporates. This cools the plant much as you would be cooled if you were in a wet t-shirt on a windy day. Wind and heat affect the amount of transpiration that occurs at any given time. Trees and shrubs have small openings in the leaves called stomata that act as windows or valves controlling the amount of water vapor and other gasses that escape through the leaves. Trees and shrubs that are adapted to dry climates will have fewer and smaller stomata to reduce the amount of moisture loss. Thick waxy leaves also reduce water leakage between cells. Hairs and thorns on leaves slow wind speed over the leaf and reduce moisture loss. If the process is running smoothly the leaves will remain cool and firm inflated with water and turgid.
The pressure that keeps the leaf firm is called turgor pressure. When the leaf can no longer get enough water it loses turgor pressure. The first thing that happens when the pressure drops is the stomata close like windows keeping water vapor in. If moisture continues to be lost the leaf droops like a limp balloon. This may happen on hot days, usually the tree recovers from its moisture deficit in the evening and processes return to normal. If water is not available the tree will continue to struggle until it takes all the available water out of the soil. Then the passive process of osmosis reverses itself and the tree loses moisture to the soil. The tree responds by shedding roots and leaves. If this isn’t enough to restore the moisture balance the plant may reach permanent wilting point. This is the end for the tree and shrub. No amount of water will help it now it’s dead.
If your plants are looking a little wilted check the soil with your digital probe, is it dry and hot? Water your plants deeply rather than frequently; let your index finger be your guide!
When in doubt ask an ISA Certified Arborist, they will have the latest information on watering.