Hemp Farming Resources
Why We Irrigate
If we were growing hemp for grain or fiber, irrigation wouldn’t be a big factor. Sow a field of regular (male and female) seeds and let nature take its course. However, growing a field of flowering female hemp plants is a different matter.
Since each plant is worth a lot of money, we want to be able to tend to each one. As in the medical marijuana industry, we strive to maximize each plant’s potential. Licensed marijuana growers in southern Colorado plant with some variation of a plastic mulch and drip tape irrigation system for large outdoor grows. Hemp growers should follow their lead.
Generally speaking, this isn’t a DIY project for anything over an acre or two. It would be smart to at least consult with an irrigation company or pay them to draw the field layout and provide a list of materials.
Basic Components of an Irrigation System
The Water Source
WATER FLOW – GALLONS PER MINUTE (GPM)
Water in sufficient quantities for the amount of acreage envisioned would be the basic calculation for setting up the whole growing plan. How much water can legally and practically be taken from the well, municipal water, stream, pond etc and at what rate? If your source doesn’t produce sufficient gallons per minute, you will have to either spend money or get creative.
How much water is needed depends on the climate, but you better figure two to three gallons per day, per plant at peak consumption. Can’t run out of water when the plants need it the most.
For a 10 acre example:
15,000 total plants to irrigate
2.5 gallons per day per plant at peak season
37,500 gallons per day
8 hour watering cycle
37,500 / 8 / 60 = 78 gallons per minute
At peak use, 78 gpm is called for. You could get around that number by increasing the watering cycle to 12 hours a day during higher use periods, then only 52 gpm would be required. Also pumping 24 hours a day into tanks or a pond will also alleviate problems with insufficient water flow.
WATER PRESSURE – PSI / FOOT HEAD
Besides having sufficient quantities of water, it must be delivered to the field at sufficient water pressure. Water pressure is measured in pounds per square inch (PSI) or feet of head. One foot of head equals .43 PSI. A 100 foot water tower will deliver 43 PSI of water pressure at ground level, size of the tank and pipe don’t matter. With irrigation, water pressure is provided by the pump(s) delivering it from the water source. Sizing of pumps, pipes, valves etc. is critical for proper installation and service. Professional guidance is recommended at this phase of the project because incorrect pressures can cause problems such as pump damage and irrigation system failure.
Pumping uphill drastically reduces PSI. A 10 foot vertical rise, or 10 head feet, will reduce PSI by 4.3, 30 PSI would be reduced to 25.7 PSI. When water flows through the system, friction from the pipes and fittings further reduce PSI. Water meters, water filters, valves and other equipment all put a ‘drag’ on the water flow and reduce the PSI even more.
The good news is drip tape irrigation only requires 12-20 PSI at the drip tape inlet, in fact Netafim’s literature shows full flow for their DripNet PC tape at 6 PSI, here’s the graph. Lack of water pressure shouldn’t be a problem if the system is designed sensibly. Typically a 20 PSI pressure reducing valve is used in front of the drip tape to protect the system from being over-pressurized.
Getting water to the fields
Before water is sent to the fields it should run through a quality water filter and be provisioned with injection ports for fertigation and ph control. A water flow meter is also a tool necessary to intelligently operate an irrigation system. Expertise is required for proper setup and successful operation at this point, but from here it can be installed anywhere from a bare-bones low cost system to a high cost automated deluxe setup.
Water is typically sent to the fields through a PVC main pipe. From there the individual zones are fed with a flexible pipe that connects to the individual drip lines laid in the rows under the plastic mulch. Each irrigation zone is typically from 2 to 5 acres or more, depending on factors such as water source, field grade and contours, overall system size, irrigation materials, etc. Each zone is operated by a valve, automatic valves require running station wire to the main controller, or the system can be operated with manual valves.
Great video showing installation of Netafim drip line irrigation on a very large scale without the plastic mulch. Shows the whole irrigation setup from the well to the drip line.
Plastic Mulch and Drip Tape
The mulch is put down based on the designed field layouts. See our page on Hemp Field Layout for more information.
Wide, raised beds are recommended. The widest plastic mulch sold is 60 inches so a 6 inch raised bed ends up about 36 inches wide. Drip tape is laid 2 inches underground below the plastic mulch and then connected to the flexible manifold pipe at both ends. Each zone requires flush valves and air vents.
A typical drip line used is Netafim Dripnet PC with a flow rate of 0.26 gph. Normally the drippers are spaced every 12 inches. With one drip line per row, on 5 foot centers, that’s 5 drippers per plant for a total of 1.3 gallons per hour for each plant. Netafim sells all the easy fool-proof connectors to go with their pipe and drip line so its a real quality setup.
Mountain Mango is some of the sweetest hemp we've produced. It sets bud really quick. Great calyx development, frosty and sticky.
A classic cross of The Wife X Charlotte's Cherries. With a sweet terpene profile, it will produce a high quality flower.