Drip irrigation delivers water slowly and directly to the plant root zone through a network of tubes and emitters. A common decision is whether the tubing should rest on the soil surface or be installed beneath it. This choice, between surface and subsurface installation, affects system performance, maintenance, and longevity. Determining the best placement requires balancing efficiency and aesthetics against practical concerns like repair and equipment needs.
The Advantages of Subsurface Installation
Burying the drip lines offers immediate visual benefits by keeping the landscape clean and uncluttered. This hidden placement eliminates the sight of plastic tubing, making the irrigation system virtually invisible. Concealed lines also prevent the system from becoming a tripping hazard in garden beds or walkways.
Subsurface placement significantly extends the lifespan of the polyethylene tubing and emitters. Plastic materials exposed to direct sunlight suffer from ultraviolet (UV) degradation, causing them to become brittle and crack. Underground installation completely shields the components from this photodegradation process.
Water efficiency is maximized when the system is placed beneath the soil surface. Delivering water directly to the plant roots minimizes moisture lost to surface evaporation and wind drift. Subsurface placement can reduce water loss from evaporation by up to 90% compared to surface application methods.
This direct delivery encourages deeper, more resilient root growth in plants. Constant moisture at the root zone trains the roots to grow downward, making plants more drought-tolerant. Keeping the surface soil dry also inhibits the germination of annual weed seeds, reducing garden maintenance.
Practical Drawbacks and Troubleshooting
One primary difficulty with buried drip lines is locating and repairing damage. Unlike a surface system where a leak is immediately visible, a break underground requires significant effort to find the exact location. This difficulty increases the time and cost associated with routine maintenance or unexpected system failures.
Root intrusion presents a significant biological challenge for subsurface systems, especially in perennial plantings. Plant roots naturally seek water and nutrients, causing them to grow into the small openings of the emitters. Once inside, the roots can block the flow of water, rendering sections of the system ineffective.
Monitoring the performance of individual emitters becomes nearly impossible when they are buried. It is difficult to visually confirm if an emitter is clogged, delivering water unevenly, or not functioning. This lack of visibility can lead to unnoticed water waste or localized plant drought stress.
Troubleshooting a pressure drop in a subsurface system is much more challenging than with a surface installation. The cause, whether a blockage, a break, or a faulty component, is not externally apparent. Identifying the source often requires specialized pressure monitoring tools or excavating sections of the line.
The cost associated with excavating and replacing damaged sections can outweigh the initial water savings. Because the system is inaccessible, any significant repair often involves disturbing the landscape, which subsurface installation is intended to prevent. Rodent or insect damage to buried lines is often only discovered after significant water loss has occurred.
Specialized Equipment Requirements
Standard drip tubing is not suitable for burial and requires specialized subsurface drip irrigation (SDI) tubing. This advanced tubing is engineered specifically to manage the stresses of underground operation. It features pressure-compensating (PC) emitters, which ensure uniform water delivery across varying elevations and line lengths.
A feature of SDI tubing is the incorporation of chemical root barriers within the emitters. Manufacturers embed emitters with slow-releasing herbicides, such as Trifluralin (Treflan). This localized chemical release creates a microscopic zone that deters roots from entering the emitter opening without harming the plant.
Because the emitters are inaccessible for cleaning, advanced filtration is a prerequisite for any buried system. Installing high-grade filters, such as fine mesh screen or disc filters, is necessary to prevent sediment and particulate matter from clogging the emitters. The filter grade needs to be finer than what is used for surface systems to protect the small openings in the PC emitters.
To manage sediment buildup within the lines, the system must include automatic or manual flush valves. These components are strategically placed at the lowest or furthest points of the drip line network. Periodically, they open to allow a high-velocity blast of water to exit the line, removing accumulated debris and silt.
Proper installation demands the use of air/vacuum relief valves at the highest points of the system. When the system shuts down, these valves prevent suction from pulling soil particles back into the emitter outlets. Preventing this soil aspiration is a mechanical defense against clogging that works in conjunction with chemical and filtration methods.
Management of Surface-Level Systems
For those choosing to keep the irrigation lines on the surface, several management practices maximize system performance and longevity. The first step involves securing the lines to prevent movement that could disrupt emitter placement or cause accidental damage. Using specialized anchoring stakes or pins holds the tubing firmly against the soil.
The surface lines should be covered with organic mulch, which serves several functions. Mulch physically shields the polyethylene material from direct sun exposure, mitigating the damaging effects of UV radiation. This barrier significantly slows the degradation process, extending the usable life of the system.
Beyond protection, the mulch layer helps regulate the temperature of the tubing and the surrounding soil. Extremely hot tubing can increase the temperature of the delivered water, which may stress plant roots. Mulch provides insulation, keeping the water temperature consistent and closer to the ambient soil temperature.
Routine seasonal maintenance is simplified when the lines are accessible on the surface. At the end of the growing season, the lines can be easily flushed to remove accumulated debris or mineral deposits. In colder climates, the tubing can be disconnected, drained, and stored indoors to prevent freezing damage.