Micro-sprinklers are a great choice when a larger volume of water is needed than standard drip emitters can provide, but a traditional spray or sprinkler body would be too large or incompatible with the irrigation area. Micro-sprinklers can be incorporated directly into a drip irrigation system as they come in a variety of connection sizes and types for easy attachment to risers or assemblies. They are commonly used to irrigate trees in both commercial and residential settings, but also work well for large densely planted landscapes, greenhouses, and even frost protection.
Most fixed and pressure compensating drip emitters deliver between 0.5 and 2.0 GPH with a few standouts able to provide up to 4 GPH, however this volume of water will not be adequate for some trees and landscaping needs. Micro-sprinklers bridge the gap between drip emitters and volume requirements. Like other drip systems, micro-sprinklers operate at low pressure. At the low volume end, micro-sprinklers deliver 5 to 6 GPH, at the high end they are capable of 40 to 60 GPH (or more in some cases), even at low pressure.
Micro-sprinklers operate at low pressure and are designed to cover a tree’s root zone. Using micro-sprinklers for tree irrigation has some advantages over tree rings. Micro-sprinklers are easier to adjust as trees mature; some come with deflectors or wedges that force the water in a trajectory designed to keep the trunks of young trees dry; as the trees mature these deflectors can be broken off to allow the water a wider spray radius. Tip: If your preferred micro-sprinkler does not come with a wedge or deflector, place a stick or similar obstacle between the trunk of the tree and the micro-sprinkler; this will act as wedge to keep the bulk of the trunk dry.
1/4" Coupling Valves can also be used to adjust water volume being delivered, particularly with larger trees. Like inline ball valves that are used to make pressure/flow adjustments in a high pressure or high flow system, coupling valves can be partially opened/closed to adjust the volume of water. When using coupling valves to make adjustments in water volume, it is best to do so when the trees are larger; if the coupling valve is closed enough to heavily restrict flow, there may not be enough pressure left to meet the minimum operating pressure of the micro-sprinkler.
Due to their small size and low cost, it is practical for each individual micro-sprinkler to receive its own coupling valve.
If the trees being irrigated are on a slope, it is best to place the micro-sprinkler uphill from the tree. There is nearly always a small amount of water that will fall close to the emitter or drip down the stake instead of spraying outward; if the emitter is uphill of the tree, this will allow that water to run downhill towards the tree instead of away. Since trees prefer to drink from the small roots growing farther away from their trunk, this will provide the best opportunity to avoid waste. On uneven topography pressure compensating micro-sprinklers should be used to account for the increased pressure emitters at the low points in the system will encounter.
Micro-sprinklers are generally placed about a foot away from the trunk of the tree being irrigated. If it’s too close, the trunk would block much of the water; too far and it won’t be able to reach areas nearest the tree. The area nearest the tree should be kept clear of mulch to reduce the risk of crown rot, particularly in heavy or clay-like soils with poor drainage.
Micro-sprinklers are often used for landscape irrigation. Shrubs, bushes, ground cover, trees, and perennials can all benefit from micro-sprinkler irrigation. In low pressure systems, which make up the bulk of micro-sprinkler systems, the water droplets created are smaller and gentle; some can be compared to a gentle rain. This allows them to be used with younger plants without worry of damage from high pressure or large water droplets. The high flow Jain AquaSmart Micro-Sprinkler can deliver 25.3 GPH at only 20 PSI; this allows your landscape plants to receive a healthy volume of water but without the increased risk of damage from high pressure sprinklers systems. Place your water loving ground cover plants near your shrubs and both can have their needs met by such an emitter.
When liquid water freezes it releases heat through a process known as heat of fusion. This heat can be used to keep temperatures at or above 32° F to prevent frost or freeze damage to both mature and young trees. Micro-sprinklers used for frost protection offer two sources of heat. In addition to the heat of fusion process, ground or well water is commonly 40° to 50° F, even when the above-surface temperature is below freezing.
This method of frost protection primarily prevents frost/ice accumulation on the trunk and lower canopy; the upper canopy does not receive significant temperature increases. As a quick example, one study found that ground level temperatures will be 2° to 5° F higher, 2° to 3° at chest height and 0° to 1° higher in the canopy. This means that this method is better for tree and leaf protection than it is for fruit protection.
To utilize this method in an orchard or grow site, large volumes of water will be needed for the entire duration of the freeze event. Common application rates are 2000 GPH per acre; at temperatures significantly lower than freezing the volume required can be as high as 3000 GPH per acre. Not only must this volume of water be delivered, but it must be delivered through the entirety of the frost event and into the next day until ambient temperatures climb well above freezing. The water must be applied to the entire acreage and needs to be continuous. Crop planting density, soil moisture levels, wind factor and wet and dry bulb temperatures are all factors that go into determining the volume of water necessary to provide frost protection.
On calm (0-1 MPH winds) nights, micro-sprinklers have been able to provide partial protection to hearty trees at temperatures as low at 17° F. Micro-sprinklers for frost protection offer lower risk in that the applied water does not come into contact with vulnerable tree tissues, rather it relies on heat of fusion to raise the ambient temperature. Micro-sprinkler frost protection systems require less water consumption than overhead systems and are often paired with wind machines since the benefits appear to be additive rather than multiplicative.
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