Introduction

Like any foundation, it creates a strong root system, highlighting horticultural strategies that affect its quality and growth, both of which are top priorities. While the roots are constantly in communication with their environment, exchanging information, the root system plays a dynamic role in the world below (Book recommended), interacting with microorganisms, soil types, and weather conditions. This complex interplay sustains the Soil-plant-atmosphere complex:  flow of water and nutrients from the soil through the plant and into the atmosphere. Water is not just a nutrient carrier

While roots respond to many signals, in this post, I will focus on one aspect: the relationship between roots and water. Plants’ roots don’t just passively absorb water, but actively respond to where and how it is provided, especially through our irrigation practices.

General Considerations

Does the  Roots Hunt for Water?

When the soil surface starts to dry out, but moisture remains deep down, roots receive a hormonal signal to grow deeper, chasing those water reserves.

Conversely, roots are also smart about growing sideways. They will actively form more branch roots in moist soil pockets while avoiding growth in dry patches. This architecture is orchestrated by several plant hormones, such as auxins and abscisic acid (ABA). They may act as messengers, traveling from the leaves and shoot tips down to the roots, telling them where to grow. Here is why one of the priorities in HLB management at earlier stages should be to maintain this hormonal balance.

Don’t Guess, Measure

UF/IFAS and other institutions have been working on strategies for low-cost and more expensive instruments, apps, and sensors, among others. We can’t truly know what’s happening in the root zone without measuring.

While many tools exist, the key is to move from guessing to data-based decision-making. For crops like citrus, research has shown that sensors using TDR (Time Domain Reflectometry) or TDT (Time Domain Transmissometry) technology can be particularly effective at providing an accurate picture of soil moisture where it matters most. We will be discussing shortly in another blog about low-cost alternatives shortly

For example, a healthy, mature citrus tree on deep, sandy soil can have roots extending five feet deep, far beyond what we can see on the surface.

The Hidden Helpers in the Soil

Roots don’t live in isolation. They are surrounded by a community of microscopic organisms that impact plant health and modify its ability to overcome stressful conditions.

Some of these microbes, called endophytes, live inside the plant and can help it defend against diseases like Huanglongbing (HLB), or citrus greening. Studies have found, for example, that citrus trees showing no symptoms of HLB often host a greater number and variety of these helpful microbes. Specifically, a bacterium called Bacillus subtilis appears to boost a citrus tree’s natural defenses, with its presence linked to milder disease symptoms.

Learning how roots work is not about stressing trees with drought. It’s about using water more efficiently and wisely.

Take-Home Messages

1. Soil moisture sensors help to decide when to irrigate, how long to run the system, and where water is needed in the grove.
2. Proper irrigation keeps oxygen in the root zone and prevents trees from reaching the permanent wilting point, which causes lasting damage.
3. Place irrigation emitters to wet the active root zone, not the trunk. This prevents stem wetting, encourages strong root growth, and improves water-use efficiency.
4. A well‑managed irrigation program:

• Reduces air bubbles(cavitation) in the tree’s sap flow
• Minimizes nutrient loss from leaching
• Supports steady photosynthesis for healthy growth and yields

Additional references and resources

• 2018_july_using_soil.pdf
• ATTRA_SoilMoistureMonitoringTools&Methods_2006.pdf
• Effect of Various Irrigation Rates on Growth and Root Development of Young Citrus Trees in High-Density Planting – PMC+
• Root Plasticity in the Pursuit of Water
• Abscisic acid dynamics, signaling, and functions in plants – Chen – 2020 – Journal of Integrative Plant Biology – Wiley Online Library
• Recent progress in the understanding of Citrus Huanglongbing: from the perspective of pathogen and citrus host | Molecular Breeding | Springer Nature Link
• Castle, William. (1978). Citrus Root Systems: Their Structure, Function, Growth, and Relationship to Tree Performance. 1978 Proceedings International Society Citriculture. 1. 62.

An Equal Opportunity Institution. UF/IFAS Extension, University of Florida, Institute of Food and Agricultural Sciences

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