Healthy pecan trees should have deep roots. The biggest obstacle for deep roots is when the soil does not allow for slow and steady drainage. This can be due to poor irrigation techniques, compacted soil, or climate.
A healthy, mature pecan tree will have a 10’ tap root. The feeder roots will typically congregate at 1-2 feet below the surface.
While pecan trees can have relatively shallow taproots compared to their height, the extensive system of lateral roots and feeder roots hold the tree firmly in place.
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Why are Deep Roots Important to Pecan Trees?
Pecan trees need deep roots to anchor and stabilize the tree. They also need to be able to reach down and collect nutrients that are not available in the surface soil.
The deeper the roots, the bigger the tree can grow, and the more nutrients the roots can absorb. This results in larger, more consistent harvests.
Pecan Tree Root System
The pecan tree root system consists of three different levels of roots:
Taproots can reach as deep as 1/4th of the tree’s height but usually hover around 10’ feet deep. Their primary function is to anchor the tree, but they also pull up water and nutrients from the subsoil.
- Lateral roots
Lateral roots shoot off horizontally from the taproot and help stabilize the tree. They develop along the taproot but are most dense between 12”-18” below the surface if the tree is in loamy soil.
- Fibrous/Feeder Roots
These are small roots that grow from the lateral roots, so the majority of them will also be 12”-18” inches below the surface. Once the tree is mature, they are responsible for collecting and delivering most of the water to the larger root system. This makes them grow up towards the surface to soak up as much water as they can.
Pecan Tree Soil Conditions and Depth
Root depth is dependent on the soil conditions. Pecan trees thrive in deep, cultivated, well-drained soil.
Pecan trees perform best in a rich, loamy soil. Loam holds water and nutrients but does not get compacted like clay. This allows for roots to have a firm grip, while also having the space to spread out.
The best soils are loamy or slightly sandy with well-drained subsoils. Silty soil along riverbeds and streams provides a good foundation, but trees planted too close to water may become top-heavy and are prone to being uprooted.
You can work with sandy soils that drain too fast if you are willing to replace the water loss with extra irrigation. However, clay soils can become compacted and will result in stunted root systems without significant intervention.
If the soil is too shallow, cannot drain (or drains too quickly with no added irrigation), and/or does not allow enough room for the roots to establish depth, three things can happen:
- The tree (and harvests) will remain small, since the root system cannot reach a good depth to stabilize a large tree.
- The fibrous roots will only be able to draw from the water and nutrients in the topsoil, where grass and small plants are competing for it.
- The lateral and fibrous roots, which are susceptible to heat damage, will suffer from being too close to the surface.
Soil Conditions in Main Pecan Tree Regions
In the States, pecan trees can grow as far north as Nebraska and Iowa, but they are more prolific in the south because of the longer, warmer summers. The southern environments vary from dry, desert areas in the west to wetlands in the east.
The soil conditions in places like California and Arizona are not generally conducive to pecan trees. However, there are some regions that contain good soil where pecan trees are grown commercially by migrants. In those regions, soil conditions for homeowners should be favorable enough for trees to establish a sufficient root depth.
In California, the San Joaquin Valley (mid-state) produces pecan trees commercially. Here, the topsoil and subsoil are loamy, which allows for deep drainage.
In Arizona, commercial production is kept to the mid-state region of Camp Verde. The best soil is found along river terraces, where the soil is alluvial (well-drained, fine soil deposited by water drainage).
Texas produces about 60,000,000 pounds of pecans per year. Fittingly, the pecan is Texas’ state tree. They produce all over the state, but if pecan trees fail, most growers cite poor, shallow soil as the culprit.
Pecan trees naturally grow best near rivers and creeks, where the soil is deep and well-drained.
South Georgia is most well-suited for producing pecan trees, although they also produce well in Mississippi and Florida. Soil types vary widely throughout Georgia, but regions like Dougherty County (southwest Georgia), where commercial growth is centered, provide great soil along riverbeds. Native trees can grow in most places except the northern, mountainous regions.
How to Encourage Deep Roots in Pecan Trees
Homeowners may not be able to cultivate, but deep irrigation will keep the roots from competing with grass and surface plants for water and nutrients. The water will flow down – taking nutrients with it – which will encourage the roots to follow.
Know Your Soil
The first step is to know what soil surrounds your tree. Dig into the soil to see how deep the “easy-to-dig” soil goes. Ideally, this should be around 3’. Lawn trees will survive with as little as 12” inches, but they will not thrive.
If you do not know your soil structure, contact your local extension office or soil conservation service. They can either test the soil or use maps to give you an estimate. This is important because different soil structures hold different volumes of moisture.
As a general rule of thumb:
- Sandy soils will hold about an inch of water per foot of soil
- Loamy soils will hold between 1”-2.5” inches of water per foot
- Hard or clay soils will hold between 2”-3” inches of water per foot
If you know your soil’s basic structure, you can plan a watering schedule that penetrates about 3’ feet deep at least once a week, and up to two times a week during late July and early September for mature trees. Depending on your soil type and rainfall, you may need to irrigate anywhere from 1”- 2” per week.
Young trees need about 2/3rd to 4/5th of the amount of water a mature tree needs.
Drip or soaker hoses are most efficient for deep watering. Circle the hose around the drip line (the end of the branches) and place hoses at intervals under the canopy; do not water directly around the trunk.
Symptom of Shallow Roots
Shallow root systems are vulnerable to hot weather, which results in scorched leaves.
When temperatures reach above 90⁰, roots near the surface can start to die, which can result in leaves that have a burned appearance.
Increase the amount of water you apply each week to encourage roots to grow deeper.
Healthy trees will grow in well-drained soil that allows roots to grow deep. Homeowners can encourage deep roots with good watering techniques. Once you understand your soil profile, you can apply the right amount of water to your tree.