Understanding Soil Composition
Critical for Success
Garden Tip
TB1482
Technical Bulletin Series

SOIL BASICS
Success with deeper roots!
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You have certainly heard that some people have green thumbs. If you were to survey them you would find that they either started with good soil, or worked their soil until it was nice and loamy with a good drain rate.
The single most important aspect towards healthy plants is their root systems? The most critical two aspects for plants to have a healthy vibrant root system are the type of soil they are growing in, and how it is irrigated.

Tolerating drought
and confined irrigation


This Senna artemisioides ssp. filifolia (formerly Feathery Cassia) is alive and actually looks similar to how it might look without any irrigation in a drought prone climate. Though these are classified as "drought tolerant", they are negatively affected by undersized root systems.

Look at the difference between these two plants!

Thriving on good distribution
and adequate deep water
This same genus & species is thriving with proper irrigation designed for the existing soil composition. Because the water is applied slowly and with a long enough run time to allow deep moisture you can see the benefit from proper irrigation that produces large healthy root systems.


For the vast majority of plants there is a huge difference between those with adequate root systems and those with small inadequate roots. This is their beauty and health! Proper irrigation means much more than being frequently watered! Two critical parameters of a healthy roots system are their depth and spread.
A ten minute irrigation or providing only a couple emitters is not going to provide the depth or spread needed for a healthy plant, especially when the soil is hard. With sandy soil and for larger plants, providing only a couple emitters will keep the root area small and the plant stressed.

When water is applied slowly (30 to 90 minutes) it permeates to a greater depth. With hard, slow draining soil this is the only way to obtain deep moisture. Also, when water is applied and distributed through a larger number of emitters, we see a healthy and wide area for those roots.

Depth of roots assures the plant will still have moist soil even though the weather has been hot. This also reduces evaporation as it cuts water expense. The width or area coverage, when complimented by depth, provides adequate root-soil volume to supply the quantity of moisture and nutrients a plants need.

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With soil composition that sits in the plant's root "happy zone", irrigation design is simpler. Still the run time and emitter count per square foot needs to match that soil. When caring for plants that are growing in poor soil; irrigation design is much more complicated. Just as with good soil the run time and emitter count need to match the soil, but if it does not match - the consequences are severe. If you really want to have plants that thrive for years, you need to start by knowing the composition of your soil. An example; you know you have hard, clayey soil - so that's good enough right? Did you know there are SIX different types of clay soil? Each one requires a different approach for proper irrigation.

It's not difficult
to find out which soil
composition type you have

The various types of soil composition are identified by their "mix" of the three soil particle size categories; Sand, Silt and Clay. To think you have "DG" (decomposed granite) does not address the particle size and permeation rate.

There are 12 identified types of soil composition in the Soil Triangle, and only four of them are within the "Happy Zone" for plant root systems. The reason for this is that either the clay or the sand percentage is too high. The soil either drains to slowly or too fast.

Roots will not grow into dry soil! Additionally; if soil has been allowed to become depleted of moisture, the root systems that had been growing in that soil will soon perish and not be able to rejuvenate.
Growing Healthy Plants
Is really a simple science

Soil Composition in Desert Climates


The "natural" process in the evolution of soil composition is for clay to rise to the top and sand (large particles) to penetrate more deeply. In regions of the Country where there is little rainfall there are few plants and not much in the aspect of root creation. Also, this soil becomes devoid of microbes and does not easily change state of composition. If sandy, it tends to remain sandy, and if clayey, tends to remain hard and high clay. If you live in an arid part of the country, your soil is likely high clay. You can NOT assume this however. Soil composition testing is not rocket science, but actually knowing the type of Native soil in your landscape will improve your chances of success ten times over!


In climates where rainfall is sufficient (30 inches per year or more and consistent year-round), slow draining soil is much less of a problem as rainfall is typically applied very slowly and the moisture has a chance to penetrate to a deeper level. Still here, very high clay is a real problem for many plant types.

In desert type climates; high levels of clay are often encountered. There are many varieties of clayey soil types (see soil triangle above), but one thing most all have in common is poor drainage. This is a real challenge to the development of new roots. When improperly irrigated the soil will not have sufficient oxygen, and plant roots suffer or die.
Native Soil
is the term used for
the existing soil

Amended Soil
is the term after mixing in
a formula of other Soil Media

Hard packed, high clay soil (poor composition) does not provide much of an opportunity for roots to grow and spread. This is simply because the moisture will not permeate throughout the soil area. The best way to create larger healthy root systems for new plants is to dig large enough holes and then PROPERLY AMEND the soil that goes around the new root ball.


When roots are shallow
soil dries quickly and the plant easily wilts!


Different types of shrubs and trees can thrive with various ratios of root system to canopy. You will often hear that roots should extend to the dripline (or "width") of the tree, yet drought tolerant plants can still thrive with a smaller ratio. This difference is factored into the Garden Calculator Pro I.


Though occurring less often, soils with very high sand ratios can also be a problem. In these soils, water and nutrients quickly leach away from the plant roots and wilting or nutrient deficiencies are likely. In each case, soil amendments are vital to correct the problem, and the formula for these amendments is vastly different.


In drought prone climates, during that time of year when rain is absent the only moisture is that applied by irrigation. Very few landscapes can schedule the irrigation to run for six or more hours (as is often the case with rainfall), and so depth of moisture becomes a major issue for root systems. Understanding this concept is vital towards having a healthy plant palette in desert and drought prone regions!
When your plants are growing in "Happy Zone" soil type, it is easy to schedule irrigation that will permeate deeply and give you the successful landscape that you desire. Still the permeation rate within this favorable zone of soil composition varies considerably. The Garden Calculator Pro I will provide the necessary details for setting up this irrigation in a way that will achieve this.
Soil Amendment Formulas differ Greatly
based on Native Soil Type

Compost - Planting Mix - Potting Soil - Perlite - Sand
Various combinations of these amendments, when mixed in with your native soil will make a "new soil composition" that provides the characteristics needed for success.

To skimp on Amendments and hole size invites plant stress & failure!

The Garden Calculator Pro-I provides complete and accurate soil amendment formulas based on input from a simple soil test the user provides. Not unusual, where the Native soil is very poor, most of that native will not be re-used in the planting hole. The proportions of native and the various amendments are specified for each planting analyzed. No guesswork involved and a complex analysis is conducted instantly. Additionally, this online calculator will provide specifications for the irrigation required.
Additional Information on these pages

When trees or large shrubs begin to show signs of stress indicating their root growth is being restricted, there are two techniques to consider for remediating this: Radial Trenching and Vertical Mulching! To understand these techniques; visit TB1483 "Bad Soil Remediation".

Being successful when installing new plants into your landscape actually involves several important considerations. In this Garden Tip the concept is Understanding How Vital Good Soil Composition is. Even if you have really good soil that doesn't drain too fast and yet doesn't drain slowly, extra organic matter (that comes from compost or planting mix) provides the food for soil bacteria to establish and grow. Living soil is one of the "keys" to success in the garden. To better understand how to AMEND the soil for your new plant; visit TB1481 "Critical Aspects for Soil Composition".