Step 1 - Understanding plant / water / soil relationships.
Understanding the way water moves through, and is stored in soils is essential to understanding how a plants can access and pull that moisture up into the leaves for hydration and growth. Soil is just like a sponge. The larger the sponge, the more water is stored.
For soils in your yard this example is best described as; “the deeper the soil profile the larger the sponge, the more moister is available for the plant roots to pull up into the leaves”.
SOIL PROFILE - The different layers of various soils from the surface down.?? For this discussion we will concentrating on the layers that concern plant growth. Those are the thatch layer (this is technically not a soil layer but it is important for our discussion), the surface of the soil, and the root zone.
An irrigation system is an imitation of natural rain.
We all know that rain is a uniform application of water. It’s the same amount in the front yard is it is in the back yard. A spray irrigation system, or one that uses pop-up spray heads to apply water is the most accurate way to imitate rain. We know this because when we were kids it was fun to play in the sprinklers because we could get wet with the sun shining to keep us warm. Playing in the rain was sometimes too cold because the sun was gone behind the clouds. This point is important due to the fact that the sun can act against us when we water by evaporating the moisture before it has a chance to enter the soil profile. We’ll get into this more in step two.??A spray irrigation system is the best type of system to have for plant growth because we know it imitates rain most accurately. However, it can be the most inefficient system due to the fact that the water is launched into the air as tiny droplets that can evaporate due to wind, heat, and soil conditions.
IRRIGATION EFFICIENCY - The application of water to your landscape with minimal losses to evaporation.
Plant roots are opportunistic.
They will grow wherever they find good conditions. The basic needs of plant roots are moisture and oxygen. Plant need oxygen to grow. Oxygen from the atmosphere can penetrate soils at the upper layers of the soil profile. How deep depends on the types of soils, textures, and other factors that are not as important as just knowing that the roots need that oxygen to grow and survive. So if your lawn is muddy or makes a squishy sound when you walk on it, it may have so much moisture that there is reduced oxygen and poor root health. Avoid over saturated soils at all times.
Most of the time we will be talking about lawns. Trees and shrubs are a little different because they usually have larger, deeper roots due to the fact that they are larger plants. Plant root size is in direct relation to the size of the plant. Duh! An oak tree or spruce have huge roots that go much deeper than your lawn. The point that I’m trying to make is that we don’t need to give extra water to trees due to their deep tap roots that can access ground water. However, new trees need some help because their roots are still inside the container or root ball, and will not be able to provide enough water to make up for the water losses of the leaves or needles. An extra drip system is a good addition to the new trees for a few years until they can get established in the landscape. Extra irrigation for larger trees that have been in the ground for years is not needed and wasteful. Most mature trees have roots that extend twice the width of the branches of the tree. Your mature trees are probably getting moisture from the irrigation you provide to the lawn anyway. Yet, trees can benefit from a mulched area at their base. This gives them a place for moisture and nutrient up-take without having to complete with lawn grasses. This may not be the look that is pleasing to you but it’s a great way to help trees to thrive. We will look at different drip systems later and how to use them for different applications and plant types later in step four.
Different soil types will absorb and hold water differently. As a rule course soils will hold less water than fine soils. We have many different soils type here in our area. You could have fine silt washed down from the mountains or pure cobble rock. Maybe you have both! New homes can have all kinds of soils types usually with a thin cap of screened topsoil applied by the landscaper during installation. I don’t want to imply that you need to spend a lot of time worrying about your soil type. You just need to keep this in mind as your irrigation system runs during the season.
The courser your soil (the larger the soil particles) is, the shorter the duration between watering times. If you have very fine, deep, silty soils you may be able to go days between watering. But only if your lawn has deep roots. If you have one of those situations with poor cobble soils with a thin cap of topsoil then you will have to work a little harder to train the lawn to grow those deep roots. The trick is to run your irrigation system for a long time (maybe 30-40 mins. per zone) and then stop watering for as long as possible so the soil can dry out. That’s right. I said 30-40 min per zone. Most people run a zone for about 10-15 min. and loose much of that water to evaporation. Plus they only end up watering the top few inches of soil. Where do you think the plant roots will grow if only the top few inches of soils are moist? You got it, at the surface. And that’s the opposite of what we want to happen!
Plant roots need dry cycles.
They harden off and get more durable when subjected to dry periods. Does it rain every day a dawn for 10-15 minets? If your a farmer that would be great. The reality is that it rains for hours and then no rain for days or even weeks. Plants have evolved over time to cope with this by growing when soil moisture is high and hardening off during dry periods to wait for the next rain cycle. Remember we want to imitate mature.
There is another benefit to dry cycles. Remember that roots are opportunistic. As the soil dries it dries at the surface first and then dries down deep. The roots at the surface stop growing as that soil dries. The roots that are deeper continue to grow because the moisture in the deeper soil layers allows that growth. Roots will also continue to grow deeper over multiple dry cycles. The result is a deeper root system. Plants don’t have minds. They don’t think about these things. They react to their environment in predetermined ways. It’s our job to manipulate that environment to encourage those plant habits. As you can see we can encourage bad habits as well if we don’t take the right steps.
In step 2 we will look at your irrigation system and how to use it to perform these procedures and best imitate natural rain with minimal losses to evaporation. The trick is to realize that we under irrigate most of the time and that you can have the confidence to apply water for over a half an hour rather than 10 minutes.
For years I worked in the interior plantscape industry installing and maintaining large indoor gardens in malls, hospitals, and restaurants. When people would ask me to look at their plants and tell them what was wrong it would usually be a simple fix of watering with more water, less often. This fear of over watering is well founded. Yet, we need to overcome that fear and let plants grow the way nature intended.
CONCLUSION - Your soils should be totally saturated without being muddy and then allowed to dry out as much as possible without wilting the plants to encourage deep root growth.
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