Tuesday, February 5, 2013
5 Drip Irrigation Mistakes to Avoid
Drip irrigation systems are very user-friendly, but the potential for costly mistakes is always a factor for the do-it-yourself installer. Here are five common mistakes and some tips on how to avoid them.
Mistake #1 – Over-Watering Your Plants
Probably the hardest adjustment when converting to drip irrigation is getting past the expectation to see a large wet spot on the ground or even puddling of water at the base of the plant, much like you see when watering by hand. Drip irrigation is a very efficient way to get water to your plant's root zone, so you don't need as much water as other watering methods. In fact, you should only see a small spot of water on the ground surface (about 3” diameter) at the dripper. The water gets to your plant's root zone by traveling vertically through the soil due to gravity and horizontally through the soil due to capillary action within the soil. To see exactly how water is permeating your soil, first run your system for 30 minutes, then shut it off. Wait another 30 minutes, then dig down below a dripper and around the plant to see the wetting area and if there are any dry spots. If necessary, you can either adjust the placement of your dripper or add another dripper. Sometimes it's best to start with a lower volume of water, monitor your plant's health frequently to see if it needs more or less water, and adjust the water volume and/or watering time accordingly.
Mistake #2 – Not Matching Your Drippers to Your Plants' Watering Needs
Different types of plants have different watering needs. If you're watering different types of plants on the same zone, you'll need to make sure you're not giving too much water to some plants and not enough water to other plants. Ideally, you would want plants with different watering needs on separate zones. When that's not feasible, you can adjust your system accordingly. For example, if you have two plants on a zone, and one plant needs twice as much water as the other, you can put a dripper with double the flow rate at the plant that needs more water. If you only have drippers with the same flow rate, you can put multiple drippers at the plant that needs more water to double the flow rate. Side note: Space your drippers at least 6 inches away from the base of established plants to avoid fungal infections and other types of diseases. Try using two drippers per plant positioned at opposite sides of the plant to promote even root growth, and if one dripper gets clogged, the plant will still receive water from the other dripper.
Mistake #3 – Exceeding the Tubing Capacity of Your System
This mistake occurs commonly when you are not aware of the system's capacity. For example, the capacity for 1/2” poly tubing is 200 feet (single run length) and 200 gallons per hour (flow rate). If you have a 1/2” tubing single run length of over 200 feet, you may have inconsistent water flow at your drip emitters due such factors as friction between the tubing walls and the water flow. If you are using drip emitters with flow rates exceeding 200 gallons per hour with 1/2” tubing, you'll also get inconsistent results. This concept is referred to as the 200/200 Rule for 1/2” tubing. For 3/4” tubing, use the 480/480 Rule, and for 1/4” tubing, use the 30/30 Rule. Of course, there are always exceptions. For example, if you have a run length of 300 feet of 1/2” tubing and you have drippers on that line with a total flow rate of only 50 gallons per hour, the low flow requirement will usually offset the friction loss in the longer run lengths.
Mistake #4 – Inadequate Water Supply Flow Rate
The flow rate (usually measured in gallons per hour or gph) from your water supply must be equal to or more than the flow rate required by your drip irrigation system. For example, if you are using 200 drip emitters rated at 1 gph each on 1/2” tubing, that equates to a total of 200 gph required by your system. Although you are within the tubing capacity, if your water supply is not producing at least 200 gallons per hour, you will experience inconsistent water flow from your drippers. For this example, you can either decrease the required flow rate of your system by decreasing the number of emitters, or you can use drippers with a lower flow rating, or you can split your system into more than one zone.
We have an easy flow rate calculator available at http://www.dripdepot.com/drip_irrigation_tools/flow_calculator
To calculate the flow rate of your particular water source, fill a bucket with the water source fully open. Time how long it takes to fill the bucket to the top. Then, enter your figures into the calculator. The results will tell you how much water is flowing out of your source over a period of time, and the maximum size drip irrigation system that your water source can service.
Mistake #5 – Water Supply Pressure is Too High or Too Low
A typical drip irrigation system needs about 25 pounds per square inch (psi) of water pressure to function optimally, but many emitters rated at 25 psi will work well at pressures as low as 15 psi. The flow output will be slightly less than at 25 psi but any difference can be made up with longer watering times. With too little pressure, you will experience inconsistent water flow from your drippers. With too much pressure, fittings may pop off and/or drippers may squirt rather than drip. For drip tape, do not exceed 15 psi to avoid rupturing the tubing.
By installing a pressure regulator rated at the desired pressure, problems with over-pressure can be avoided. Problems with under-pressure are a bit more complicated. Please note that most municipal water supplies are at least 40 psi. Where we see the low pressure issues are mainly with wells and water tanks. If you have concerns that your pressure is too low to properly support a standard drip irrigation system, you can always consider a system specifically designed for low pressure water supply applications, like rain water catchment or other containment systems.
Many of these mistakes can be avoided by spending a little bit of time planning your system. We have compiled all our planning resources in one easy location for your convenience. http://www.dripdepot.com/article/drip_irrigation_online_classroom.
We love getting feedback, so please feel free to share your experiences on this topic, whether or not you found this article helpful, and if there are any specific topics you would like us to cover in the future.
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