Although in the Charlottesville area we get a good amount of rain throughout the year, still there are dry periods during the growing season when our plants may suffer if they don’t receive additional irrigation. For the reasons explained below, there are many advantages when home vegetable and landscape gardens are irrigated using drip irrigation rather than hand watering or spray-irrigation methods. Please note that this article is intended as a general guide for home garden irrigation only, which excludes home lawns or commercial agriculture, because they have different system requirements. Detailed information on the topics discussed here are available on the websites listed in the reference section at the end of this article. Also, the Piedmont Master Gardeners Help Desk is available to answer any questions that you may have. The best way to send your questions to us is by email at albemarlevcehelpdesk@gmail.com.
I installed my first drip irrigation system when I lived in California. At that time, local water conservation regulations limited landscape irrigation to twice a week during certain days and times. I decided to convert my lawn to a garden of mainly native plants that could be irrigated by a drip system for water conservation. During my research I became aware that, in addition to water conservation, drip irrigation (also called micro-irrigation) had many other advantages. Although professional installation of drip systems is available, most home gardeners should be able to plan, install, and maintain their own drip irrigation system after doing some research.
Benefits of Drip Irrigation
A drip irrigation system with a timer can be programmed to automatically deliver water from a suitable water source through a network of plastic tubes and emitters to the root zones of landscape plants. The timer can be programmed for start time (say 6:00 AM); run time (say 15 minutes); and frequency (say once every 3 days). Having full control over the time and amount of water delivered to each plant, the gardener will benefit as follows:
- Water is delivered directly to the root zone, eliminating runoff, overspray, excessive evaporation, and over-watering. Significant water conservation is achieved by this method.
- Full control over watering amounts and frequencies result in consistently uniform soil moisture, and therefore healthier plants.
- Flowers, leaves, and stems of plants stay dry and are less susceptible to fungal diseases.
- Weed growth is minimized in bare areas of the landscape beds because they are not watered.
- Very early in the morning is the best time to irrigate plants, and this is easily achievable by setting the start time on the timer.
- Drip irrigation is very versatile and can be configured to water a variety of landscape shapes and sizes. A single potted plant, a vegetable garden, annual and perennial beds, and young trees can all be connected to a drip irrigation network. You can start with a small project and as you gain experience, and when needed, the same system can be gradually expanded as necessary.
- Drip irrigation pipes are typically laid on the ground and don’t require digging. They can easily be re-configured as needed to accommodate any changes. Repairs are also very easy due to the same reason.
- Timers with multiple outlets allow for zoning of plants with differing watering needs. Each zone can be programmed for its optimum frequency and run time.
Drip Irrigation System Components
A wide range of materials and equipment from simple to very sophisticated are available on the market. Here I have briefly described what I used for my garden, and I think will sufficiently serve most home gardens. Details, photos, and specifications of each component are readily available on the internet for interested gardeners.
Components are connected together either by hand-tightening of screw joints; pushing together of compression joints; or punching a hole in the tubes and inserting emitters. Not many tools are needed and most of them you probably have. The only tool that you will probably need to buy is a tube hole-punch.
The basic components of a typical home garden drip system are:
- A reliable water source with clean water at a pressure of at least 25 PSI (Pounds per Square Inch), such as a regular wall hose bib. Municipal water is generally suitable for use in drip irrigation. If you use well water, special attention should be paid to suspended or dissolved elements that can cause clogging of small pipes and fittings. These elements may include minute suspended particles that can pass through the filter (such as in murky water); algae; or dissolved compounds of calcium and magnesium that have a tendency to get deposited within the system.
- A brass 2-way Y connector with shut off valves. One branch is used to connect the drip irrigation control assembly and the other is for a regular hose connection in case needed for other purposes.
- A battery-operated timer. A timer is used to automatically start irrigation and run for preset times and frequencies. Timers are available with up to four outlets, each for a different irrigation zone.
- A backflow preventer. This device prevents any potentially contaminated water left in the drip system from reentering the house water supply system, and is necessary for health reasons.
- A pressure regulator. This device reduces the source water supply pressure (which is typically between 40 to 60 PSI) to 25 PSI, which is the recommended safe water pressure for most drip irrigation components and joints.
- A filter. A filter captures any small particles that may be present in the water supply lines and prevents the clogging of dripper holes. Filters need to be inspected and cleaned periodically.
- A tube adapter. All the above parts have screw type joints which are hand tightened. The tube adapter has one end as a screw joint and the other end as a compression joint, which allows a drip tube to be connected.
- Distribution tubes. Distribution tubes consist of a combination of various size tubes commonly made of polyethylene. They convey water from the control assembly (items 1 – 7 above) to points near each plant. Mainline tubes make up the backbone of the network and may be made up of ½ or ⅝ inch diameter tubes. They are laid on the soil surface along the perimeter of the garden or snaked through it to reach the maximum number of plants without having too many elbows or sharp bends. The ¼ inch tubes, also called microtubes, can branch off from mainlines to deliver water to plant root zones. Emitters (as described below) can be installed at any point along mainlines or microtubes. The length of each mainline from the control assembly to the farthest end of that mainline should not be more than 200 feet; the total flow rate should not exceed 120 GPH (gallons per hour). Microtubes should be limited to 25 feet in total length (measuring from its connection with a mainline to the farthest end of the microtube), and its flow should not exceed 12 GPH.
- Driplines are ¼ or ½ inch diameter tubes with embedded emitters at equal spacing. They are used for row crops such as vegetable gardens or around trees. Soaker tubes are made of porous rubber and discharge water all along their length. Their rate of discharge is not predictable and therefore are not widely used; however, they may be useful under special circumstances.
- Emitters. Emitters deliver water to plants at a pre-set rate. They are small plastic parts that are inserted into mainlines and/or at the end of microtubes and discharge water at the point of delivery. Emitters of different sizes are identified by their GPH ratings, and some common ratings are 0.5, 1.0, and 2.0 GPH. I personally prefer to use 2.0 GPH emitters as much as possible because they are less prone to clogging than smaller ones. There are two types of emitters, i.e. pressure compensating and pressure sensitive. Pressure compensating emitters deliver the nominal flow rate irrespective of changes in water pressure caused by elevation changes or friction losses in the mainlines. Pressure sensitive emitters do not have this ability. There are many other types of emitters on the market such as spray emitters and adjustable flow emitters, which may be useful in special situations.
- Fittings. The availability of many fittings for mainline and micro tubes makes the drip irrigation system very versatile, and allows for easy repairs. Such fittings include elbows, tees, couplings, end caps, and adapters of different sizes.
Setting the Timer
The goal in establishing a watering routine is to keep the soil uniformly moist (not too dry and not too wet) during the dry season in such a way that plants don’t show any signs of under- or over-watering (wilting, scorching, yellowing leaves, or leaf drop). A simple method for setting the timer is to estimate an initial frequency and run time on the timer and observe the results in the garden. Then adjust the timer and/or number of emitters until you find the optimum setup after a few iterations. As a rule of thumb, watering 2 or 3 times a week totaling about 1 inch of water is enough to keep most plants happy. However, several factors, including atmospheric conditions, soil type, plant type, plant maturity, etc. make this method approximate. A more accurate method is to follow the step-by step procedures described in the Appendix at the end of this article.
Drip Irrigation System Maintenance
Drip irrigation system components are delicate and can be easily damaged and lose their proper function. Regular inspection and timely maintenance, which are easy to do, will ensure delivery of adequate water to your plants. Maintenance at the beginning of each growing season includes putting new batteries in the timer; setting timer parameters; checking the filter to make sure it is clean and not damaged; flushing the main lines and checking for any leaks along the main and micro tubes; and checking all emitters to identify and replace clogged ones.
During the growing season, occasionally check the timer battery and filter; periodically check soil moisture and make timer adjustments if necessary; check plants for any signs of inadequate or excessive watering; check for any damaged main or micro tubes and make necessary repairs; and cover main lines with mulch to protect them against the elements.
At the end of the growing season, remove the control assembly and store it in a dry and clean location for the following year; remove timer batteries; clean the filter; flush the main lines after removing the end caps; drain the main lines and replace the end caps.
Final Thoughts
My own experience with installing and using a drip irrigation system was very positive, and I hope it will be just as positive for other gardeners. In view of growing concerns about plastic pollution in agriculture, it should be noted that the polyethylene tubes used in drip irrigation systems can be recycled at the end of their lives. See “The Basics of Micro-Irrigation,” (2023) (“Drip tubing is typically made from polyethylene plastic that can be recycled. Some drip tubing manufacturers offer recycling of tubing, hose or tape.”)
APPENDIX:
For the most accurate method of setting the timer, use the formulas set forth below, which take into account the loss of moisture to the atmosphere:
Moisture is lost to the atmosphere from soil surfaces and plant leaves. Rain replenishes some of the lost moisture but during periods of draught soil moisture should be maintained at the optimum level by irrigation. The following paragraphs explain how to estimate and supply the correct amount of irrigation water in the absence of rain during the growing season. Plants should receive enough water to compensate for the loss of moisture to the atmosphere through evaporation from soil within their root zones, and by transpiration from their leaves. The sum of these two quantities is called evapotranspiration (ET). ET depends on many factors, including solar radiation, temperature, humidity, wind, and plant type, and varies throughout the year. Calculating ET for any given situation and time requires processing large amounts of data and is very complicated and time consuming. However, we can make educated estimates. These estimates can then be verified by periodically measuring soil moisture and adjusting the amount of water supplied. This method can provide an accurate and practical tool for home gardeners. The best available study for ET that can be used for Albemarle/Charlottesville area was done by the Northeast Regional Climate Center (NRCC) and its results are available on the Cornell University’s website at the following link: https://www.nrcc.cornell.edu/wxstation/pet/pet.html . The study area does not cover Virginia, however, the proximity of Washington DC to Albemarle County and the similarity of climates can justify using the DC numbers as the best estimate for Albemarle county.
—-Estimating Evapotranspiration (ET) – According to the Cornell study, the highest potential average ET for Washington, DC occurs in the month of July and is 4.66 inches per month, or 0.15 inch per day. We can use this number for Albemarle County as well.
—-Estimating daily water demand – The daily water demand for any given planted area is equal to its daily evapotranspiration (ET) and can be calculated by the following formula:
Note: In the following formulas, the number 12 is to convert inches to feet, and the number 7.48 is to convert cubic feet to gallons.
Daily water demand (gallons per day) = (0.15 ÷ 12) x Area* (in square feet) x 7.48
Thus, for a 32 square foot vegetable garden, the daily water demand will be:
(0.15 ÷ 12) x 32 x 7.48 = 2.99 gallons per day.
∗ For plants spaced closely together such as vegetable gardens, “Area” is the total planted area; while for individual shrubs or trees spaced apart, “Area” is the surface area under the plant canopy. It is not necessary to calculate areas for each individual plant; rather, plants should be divided into different categories of approximately equal drip-line area such as annuals and perennials, shrubs, trees, etc., and an average area designated to each category.
Controlling water supply – Water supply can be controlled by adjusting settings on the timer and/or selecting the size and number of emitters. Timer settings control water to the whole zone, while the size and number of emitters only affect an individual plant or a section of the planted area. In order to ensure that the water supply adequately meets the water demand, follow the procedure described below, paying attention to units of days, hours, or minutes:
—-Zone flow rate – Multiply the number of emitters in the zone by their nominal flow rate (in gallons per hour) and convert to gallons per minute. For example, if there are 32 emitters with a flow rate of 2 gallons per hour, the zone flow rate will be (32 x 2) ÷ 60 = 1.07 gallons per minute. If there are several emitter sizes in one zone, repeat the same operation for each size and add all together.
—-Watering frequency (how often) – Decide on how often you want to water your plants. Typically, shallow rooted plants such as vegetables and annuals require more frequent watering (daily or once every two days), while deeper rooted plants such as established perennials, shrubs, and trees can do well with less frequent watering (once every two to three days or even more). In the following formula, for “watering frequency“ use 1 for everyday watering, 2 for once every two days, 3 for once every three days, etc.
Run time or watering duration (how long) – To calculate the run time, use the following formula:
— –Run time (minutes) = Daily water demand (gallons per day) x watering frequency ÷ Zone flow rate (gallons per minute)
——In the example above for Estimating Daily Water Demand, the daily water demand was calculated to be 2.99 gallons per day, and let’s say watering frequency is 2, with zone flow rate of 1.07 gallons per minute.
The run time will be: (2.99 x 2) ÷ 1.07 = 6 minutes.
— The calculations above provide an estimate for the initial setting of the timer. With the help of a soil moisture meter, and periodic observations, determine if your plants receive enough water or not; and if necessary, adjust your timer settings and/or the number and size of your emitters. Also remember that plant daily water demand changes with climatic conditions throughout the year. For example, the NRCC study referenced above shows that ET for Washington, DC during April and October are 2.73 and 1.89 inches per month or 0.09 and 0.06 inches per day respectively. These numbers should be used for ET instead of 0.15 if we want to calculate the daily water demand for April and October respectively. ET for the months of May to September, inclusive, are fairly constant, around 4.66 inches per month.
SOURCES:
Featured Photo: Khosro Aminpour
“Drip Irrigation,” University of Rhode Island
“Drip Irrigation for Home Gardens,” Colorado State University Extension
“Drip Irrigation for the Yard and Garden,” Washington State University Extension (free download)
“Drip Irrigation: The Basics,” University of Arizona Cooperative Extension
“Agricultural plastics as a potential threat to food security, health, and environment through soil pollution by microplastics: Problem definition,” www.sciencedirect.com, Science of the Total Environment (Vol. 892, September 2023)
“The Basics of Micro-Irrigation,” (University of Wisconsin 2023) (“Drip tubing is typically made from polyethylene plastic that can be recycled. Some drip tubing manufacturers offer recycling of tubing, hose or tape.”)
