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Since 1970, W. P. Law, Inc. has helped meet the needs of growers by offering professional products and services. This guide has been developed to help take the guesswork out of greenhouse irrigation. Properly irrigating a greenhouse can seem overwhelming. With so many options and products available, it’s easy to get confused. This guide is designed to meet the needs of the majority of greenhouse applications to ensure proper watering of your crop.
Micro-sprinklers for greenhouse watering and misting can be mounted hanging down from overhead supports or they can be attached to risers that come up from the bench. The setup you choose may depend on the design of your greenhouse and bench layout. The same sprinklers or misters can be installed either upright or upside down.
When hanging sprinklers or misters from overhead supports, the use of a leak prevention device or LPD is recommended. This device prevents water in the overhead piping from leaking out each time the system is turned off, as well as preventing draining water droplets from causing erosion damage to the soil media below. It will also allow each sprinkler or mister to turn simultaneously at start up since the overhead lines remain full. This is especially important in propagation where frequent irrigation cycles are necessary.
LPD
Overhead Applications
For overhead applications, polyethylene tubing is recommended. The tubing can be secured to overhead supports. To attach the sprinkler or mister, a barbed drop assembly with sprinkler can be inserted into the tubing.
Inverted Sprinklers on Tubing
Upright Applications
For upright or bench mounts, PVC pipe can be run along the floor of the greenhouse or mounted to the bench with risers for each sprinkler or mister.
Upright Sprinklers on Riser (PVC)
| Sprinklers for General Watering |
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| Sprinkler | Flow Rate (GPH) |
Bench Width (ft) |
Sprinkler Spacing (ft) |
Height Above Crop (ft) |
Precipitation Rate (in/hr) |
# of Rows |
| GHSGREEN | 10.9 | 4 or less |
3 | 2 to 4 |
0.98 @ 2' above crop |
1 |
| 0.80 @ 4' above crop |
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| GHSORANGE | 19.0 | 5 to 8 |
3 | 2 to 4 |
1.20 @ 2' above crop |
1 |
| 1.10 @ 4' above crop |
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| Misters for Propagation, Cuttings, and Seeding |
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| Mister | Flow Rate (GPH) |
Bench Width (ft) |
Sprinkler Spacing (ft) |
Height Above Crop (ft) |
# of Rows |
Lateral Spacing (ft) |
Distance from edge of bench (ft) |
| GHMPURPLE |
9.2 | 4 or less |
3 | 3 | 1 |
------ | ------ |
| 5 | 3 | 3 | 2 | 2 | 1.5 | ||
| 6 | 3 | 3 | 2 | 3 | 1.5 | ||
| 7 | 3 | 3 | 3 | 2.5 | 1 | ||
| 8 | 3 | 3 |
3 | 3 |
1 | ||
| Greenhouse Parts Available |
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| GHMPURPLE | GHLPD |
4/7TUBE |
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| GHSGREEN | GHSORANGE | GHMPT05 | GHDROP12 |
GH4/7TB |
GHBB |
| GHDROP24 | |||||
For smaller hobby greenhouses that may not have access to 120VAC power, an automatic hose faucet timer can be used to automate the irrigation. The automatic timers screw directly to a hose faucet and are powered by (3) AA batteries. These timers are limited to a maximum flow rate of 5 gallons per minute (300 gallons per hour). They can be programmed with 3 start times per day with run times from 1-99 minutes. This makes them suitable for general watering, but not for propagation.
HFTIMER
For medium to large sized greenhouses, the use of an automatic irrigation controller, such as an Irritrol JR-Max, will be required. This controller is capable of running up to 8 zones. There is a “loop” function that allows you to run an unlimited number of start times per day, with run times being as little as 1 second. This makes this controller perfect for propagation and general watering.
JRMAX-8
Greenhouse sprinklers and misters require a minimum filtration of at least 120 mesh (125 micron) to prevent plugging. Filters are available in various sizes depending on flow rate.
Y-Filter Lakos Twist II Clean
| "Y" Filters |
Lakos Twist II Clean |
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| Size | Max GPM |
Max GPH |
|
Size |
Max GPM |
Max GPH |
| 3/4" | 9 | 540 |
3/4" |
20 |
1200 |
|
| 1" | 18 | 1080 | 1" |
30 |
1800 |
|
| 1 1/2" |
50 | 3000 | 1 1/2" |
60 |
3600 |
|
| 2" | 100 | 6000 | ||||
Pressure regulators are used on greenhouse irrigation systems to maintain consistent pressure and to prevent damage to system components such as tubing, misters and sprinklers. Sprinklers and misters perform best between 30-40 psi. Pressure regulators are available in various output pressures and flow rates. The most commonly used pressure regulators are 40 psi and are available in low and medium flow.
Pressure Regulator
| Pressure Regulator Flows |
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| Regulator Model |
Size |
Flow Range (GPM) |
Flow Range (GPH) |
| Low Flow 40 psi |
3/4" |
0.1 - 8 |
6 - 480 |
| Medium Flow 40psi |
3/4" |
2 - 20 |
120 - 1200 |
Use the charts below to correctly size tubing or pipe based on the flow of your system.
| Tubing |
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| Size | Max Flow (GPM) |
Max Flow (GPH) |
Max Pressure (psi) |
| 16mm (5/8") |
4 |
240 |
60 |
| 20mm (3/4") |
7 | 420 | 50 |
| 26mm (1") |
13 | 780 | 45 |
| PVC Pipe, Schedule 40 |
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| Size | Max Flow (GPM) |
Max Flow (GPH) |
| 1/2" |
4 |
240 |
| 3/4" | 9 | 540 |
| 1" | 12 | 720 |
| 1 1/4" |
22 | 1320 |
| 1 1/2" |
30 | 1800 |
| 2" | 50 | 3000 |
