CHECK YOUR EMITTERS

There are two main types of drip emitters: dripline emitters and point emitters.

Dripline (built-in) emitters have drip emitters located at regularly-spaced intervals along a distribution pipe as in Fig 1. Dripline systems are best suited to linear features such as hedges or areas of high-density planting of plants that all require the same amount of water such as a vegetable garden. Dripline emitters formed into a circle are useful for watering large pots or trees. Dripline emitters are available in a variety of spacings from 6” to 24”+ and a variety of flow rates from 0.25 gal/hr to 1 gal/hr.

Point source drip emitters are more versatile and useful for most xeriscape designs which feature plants spaced out in informal, natural looking patterns. The emitters generally come in 3 flow rates: 0.5, 1.0 and 2.0 gal/hr. Fig 2 shows an example. They can be tapped directly into larger-diameter flexible supply lines (polyethylene tubing), or they can be run off ¼” spaghetti line that is tapped into the larger supply line. Knowing how many individual emitters can operate off larger or smaller diameter pipe sizes, can be determined with some simple math. Flow charts and irrigation distributors can help you find out how much water can safely flow through whatever size of tubing you are working with. As you add individual emitters, keep a tally of how much water they require in total. Make sure that the total water required by the emitters, does not exceed the water available through your supply line. For example, a typical black poly distribution pipe with an inside diameter of ½ inch should have no more than 300 one gallon per hour emitters to ensure the zone will operate properly.

It is nice to have a detailed plan showing the location of all the distribution lines, emitters and flow rates. This makes it easier to check and maintain the system. Most information is available online or through an irrigation distributor, to determine what kinds of emitters have been used in your garden and roughly where they are located. Point emitters are often colour-coded for their flow rate and have a number stamped on the plastic (small print and may be in gallons or liters). Dripline emitters are generally not marked with flow rates.

Understanding the flow rates of your emitters or built-in dripline, is required information for matching the amount of water delivered, to the plant water needs. There is a lot of variety on the market. I have attached a short video “Drip Emitters in Action ” that shows 5 emitters in action. The three point emitters are colour-coded: red, black, and blue for 2.0, 1.0, 0.5 gal/hr. flow rates respectively. There are also two dripline emitters in the video. The one in the middle is 0.25 gal/hr. and the one on the right is 0.5 gal/hr. For dripline emitters, there is generally no way of telling what their nominal flow rate is unless you have this information from when the product was purchased The two in this video look identical but one is half the flow rate of the other. If you do not know the flow rate, schedule as if the emitters have a 0.5 or 0.6 GPH rate and monitor the soil moisture and plant material.

Almost all the point emitters on the market at this time are pressure regulated which means that regardless of being at the beginning or the end of the line, or at the top or bottom of the hill they will drip at a constant rate. The same is not true of built-in dripline. Many of these are not pressure regulated and so their rates can vary quite a bit from the specifications depending on where they are located.

Generally, you should keep your emitters above the soil level to avoid roots getting in and clogging the flow. For aesthetic reasons, the supply lines are often placed under mulch which is less likely to create issues and generally allows for easy access to “expose” and check the tubing from time to time.

CHECK YOUR ZONE FLOW RATES

As mentioned above, it is a good idea to know the flow rate of each emitter and then by adding up all emitters within a zone, you will know the flow rate for each zone. Zone flow rates matter because the total amount of water flow you have available for each zone, is restricted by how much your house water supply can provide, and by the size of the supply lines you install. If the emitters on a zone require more water than you have available, the zone will not perform well. Once you have established the total zone flow(s), you can write it down beside the controller and periodically check the rate (at least once a year). If the flow rate is higher than normal you should look for a leak. If it is lower you should clean your filters, check for kinked lines, and check for plugged emitters.

Checking the flow rate is easy with modern water meters. Pick a time when none of your other appliances is using water and then shine a flashlight on the meter. The rate should be showing 0.0000 cubic meters m3/min. It may be slightly higher if you have a slow leak inside your house such as a leaking toilet. Then go and turn on your drip zone and wait for a couple of minutes for the flow to stabilize. You should see a rate of approximately 0.0150 m3/min which equates to 15 liters/min for your drip zone depending on how many emitters you have. Note that if you have a flow rate of more than 20 liters/min and you are using a single ½ inch poly line, you may have too many emitters on your line.

If you have an older water meter you must calculate the flow rate yourself, but it is not too big a deal. Meters in Canada are all set in cubic meters, and mostly they have an odometer type numeric readout. There is some variation in the precision of the numeric readout. Sometimes it shows two decimals, or three, or four. Note carefully where the decimal point is on your meter. Use a watch with a second hand or the timer on your phone. Turn the zone on and then wait for a couple of minutes for the flow to stabilize. Take a reading of the numeric readout and then take a second reading one minute later. Subtract the two numbers and you have your flow rate in m3/min.

ADJUST CONTROLLER TIMING

This is where you can save money and conserve water.

Irrigation frequency, start times, run times, and seasonal percentage are the four main adjustments to most irrigation controllers. Some controllers have a rainfall adjustment, but these are not particularly useful in the Okanagan because most of our effective precipitation tends to happen in the months when the irrigation is off or at a low setting.

Irrigation frequency (weekly, daily, etc.) is mainly controlled by your soil texture and plant types. It can also be controlled by local watering restrictions. Good loam soils can often be watered just once a week for a relatively long run time. Clay soils will need shorter, more frequent watering so that the water does not pool and run off. Very sandy soil will also need more frequent watering (perhaps every second day) because much of the water will tend to go straight down below the normal root zone. Plants with deep root systems will be okay in this scenario. Containers also tend to need more frequent watering because of their limited storage capacity.

Start times are relatively straightforward. Except for special situations, irrigation is generally set to run at night when evaporation is lowest. Again, this may be influenced by local watering restrictions.

Run times per zone are the primary controls for how much water you use. If we could get everybody’s run times optimized, it would make a huge difference to water bills and water usage. This topic can get complicated and so I am going to give a couple of guiding principles here and then create a separate blog article to address some of the complexity.

If you have point emitters, then use the fact that a single small shrub or large perennial that is a moderate water user, and is well established, will need about 2 gallons of water per week in Kelowna in July. Larger shrubs will need 4 gallons. This means that you should be running each drip zone for a total of two hours per week if you are using 1 gal/hour emitters. That could mean twice per week for 60 minutes per zone.

If you have a dripline system, then it makes more sense to use a square foot rule of thumb. Moderate water use plants that are well established will generally need about 0.6 gallons of water per square foot per week in Kelowna in July. This means that if you have a dripline with 1-gallon emitters built-in and the emitters are spaced 1 foot apart and the lines themselves are spaced 2 feet apart then you only need your zone to be on for a total of 60 minutes per week in Kelowna in July.

Seasonal percentage is an important parameter that is often neglected. Fig. 4 shows the variation of evapotranspiration (soil moisture evaporation plus plant transpiration) in Kelowna as a function of the time of year. This is measured in mm of moisture per day, and it relates directly to how much water is being used. This actual evapotranspiration varies a bit from one year to the next, but the overall pattern is very strong. July is the highest month for water use whereas September only requires 55% of the amount of water used in July. The averages for the main irrigation months are:

April – 55%
May – 75%
June – 90%
July – 100%
Aug – 90%
Sept – 55%

It is interesting to compare the rainfall chart for Kelowna for 2020 (Fig. 5). Note that the scale is the same between this chart and the previous chart for evapotranspiration. There were only 8 days with over 3 mm of rain in the late spring and summer in Kelowna whereas every day lost more than 3 mm of water to evapotranspiration. 2021 has been even worse. This is why we are so dependent on irrigation and why installing efficient irrigation and maintaining and scheduling correctly, matters so much.

Fig. 4  – Daily Evapotranspiraton for 2020 and seasonal percentages

Fig. 5 – Daily precipitation for 2020 in Kelowna

Hopefully this article will provide some knowledge to help properly maintain your drip irrigation system and provide a beautiful garden without wasting water.

Article and Photos by Mark Godlewski

A good understanding of your soil is one of the keys to successful gardening, especially if you are committed to following xeriscape principles. In Part I, I provided some general information about soils in the Okanagan. Here in Part II, I will suggest some methods for evaluating your own particular soil.

From a gardener’s perspective there are three key soil parameters: pH, nutrient level, and texture.

The pH of soils: in the Okanagan basin soils are almost invariably alkaline. This is typical of areas of low to moderate rainfall. Even if you somehow had neutral or acidic soils, our water is alkali so the soils will soon change. This alkalinity is not generally a problem. It gets reduced to some degree by the addition of organic material. The plants that really like acid soil such as azaleas and blueberries also love moisture and so are not good candidates for a xeriscape garden.

The nutrient level of soils: in the Okanagan is variable. The glacial silts and sands of many of our subsoils are low in nutrients and organic content. As a result, most gardens have a fair bit of variability within themselves with respect to nutrients and, in fact, while some xeriscape plants like rich soil, others really prefer poor soil. For plants that like rich soil it is a good idea to constantly add organic material. More about that below.

Soil texture: is an important topic for gardeners. Examples of soil textures are sandy loam, silty clay, etc. There are 13 of these terms and they are shown on the soil texture triangle Fig 1. It is worthwhile for every gardener to know their soil texture because it has a strong impact on how you handle the soil, how you irrigate the soil and how well your plants perform. Generally, you would like your garden soil to plot in the parts of the texture triangle that contain the word “Loam”. For example the soil you see in the cover photo of this blog is a sandy loam (Gammil type) in Kalamoir Park. 

Fig. 1 – Soil Texture Triangle

To gauge your soil texture, one of the first things you can do is to select a couple sample areas that are representative of your garden. For example, I live in a house with a walkout basement. The elevation of my back garden is lower than the front and the soils are quite different between the front and back because of this elevation difference. Also, after the foundation was finished some sandy fill was brought in and used around the foundation in the front garden. Often backfill just uses the subsoil from digging the basement but it is not uncommon for some of the backfill to be brought in. Although I requested a thick layer of topsoil, it is a bit of a rare commodity in these parts. There are quite a few areas where the landscaper only put in 4-6 inches of topsoil over the subsoil. For my representative sample areas, I have chosen a location in the front garden and one in the back. They are located far away from the foundation, from the hardscaping, and away from any large trees or shrubs that required a lot of digging when they were put in.

In each sample area you want to dig a hole at least 8” in diameter. Do your best to dig down to a depth of about 12”. As you dig note the thickness of your topsoil. There is usually a marked difference in colour and texture between the topsoil and subsoil. The topsoil is almost always darker and more organic. Take a representative sample of the topsoil and subsoil and put it in a plastic bag marked with the location.

Glass jar method for texture – If you look on the web you will find several different sites that explain how to find your soil texture by mixing soil and water in jar and watching how it settles. Although this method is clean and effective for some soils, it has a couple of serious problems. If there are a lot of fine particles (fine sand, silt, and clay) and if they are all similar in colour it can be exceedingly difficult to see the sediment/water contact or the silt/sand contact in your jar at any given time. The bigger problem is that in parts of our valley the glacial clays tend to easily mix with and coat the glacial silts so that they settle together as a single unit in the mixing jar. This means you cannot use this jar method to reliably distinguish between clay and silt and therefore you cannot determine the true texture of your soil. The jar method is somewhat useful, however, in terms of providing a measurement of the quantity of sand and organics in your soil. The sand sinks to the bottom in about 30 seconds and the organics form the darker material that floats on top or settles gently on sediment after a day or so.

Handheld method for texture – This is a better method for estimating soil texture, and it involves getting your hands dirty by playing your soil. The method is well demonstrated in this link from  Australia . It is quite effective at estimating relative clay and silt percentages which people often struggle with. Silt can be mistaken for clay, but it is generally more benign. You can get an idea of what the results from this method look like from Fig 2. If you are careful with your observations, you can locate your topsoil and subsoil quite nicely on the texture triangle.

Fig. 2  – Soil Extrusion Textures

Percolation tests for texture – Percolation tests are strongly correlated to soil texture. In many ways, they are the most useful measurement because they are simple and direct. You can perform one easily using the same holes you dug to get the topsoil and subsoil samples. Make certain that the hole has relatively straight sides, is about 12” in diameter and 8”-12” deep. Carefully fill the hole with water and leave it overnight to saturate the soil. The next day fill the hole again and lay a straight edge across the top (see Fig 4). Measure the level of the water down from the straight edge in inches. Come back in an hour and measure how much the water has gone down. You can come back again after two hours and measure again to get the average number of inches per hour for your Perc test. Generally, a rate of between 1 and 4 inches per hour is considered acceptable for most plants.

One thing to keep in mind about percolation tests is that they are affected by shallow water tables. If the water table is within about 20 inches of the bottom of your hole, then it can slow down the percolation flow appreciably.

The effect of texture on irrigation – Your soil texture controls how water permeates your garden. A nice illustration of this (Fig. 3) comes from a particularly useful publication from the University of California Santa Cruz

Fig. 3  – Water Movement in Soil

UnH2O garden – It is interesting to apply these texture analyses to the UnH2O garden. I performed this analysis in two different locations in the garden (Fig 4 and Fig 5) and got similar results. We know from Part I of this blog that the garden is in an area where the subsoil texture should be a loam (sandy loam, loamy sandy, silty loam) which is popular with most plants. On the other hand, the percolation tests in the UnH2O garden gave a drainage of just 1.5 inches per hour which is on the low side of the preferred range. While the texture of the soil is reasonable the problem is that the water table is quite shallow in this part of the city. You can contrast that with my “vegetable garden” in West Kelowna 100m above lake level where I measured a drainage rate of 11 inches per hour. I clearly have a problem with my subsoil in that part of the garden and have plans to fix that immediately.

Fig. 5 – Water filled percolation hole

Improving your soil – It turns out that the recipe for improving your soil is remarkably similar for most of our soils in the Okanagan. In almost all cases you should be adding organic matter. If the soil is too sandy add composted organic matter to slow down drainage and improve the nutrient level. If the soil is low in nutrients, again adding organic matter will help considerably. It is a good idea to work some of the organic matter into the soil and lay 3” of organic mulch on top.

Clay soils also benefit from the addition of organic matter to improve the drainage. These soils are difficult to work with, however, because it is hard to effectively incorporate materials such as coarse sand and organics into clumps of clay. Clay soils will hold moisture for longer, but it is hard for many plants to access. Irrigation water can run off instead of penetrating, and walking on wet clay soil leads to over compaction.

If you suspect that you have a problem with a high water table then the best solution may be to build raised beds of loam. This will allow your plant root systems to penetrate as far as they want to get the moisture level that they prefer.

Get to know your own soil characteristics and you will find that your knowledge will pay big dividends in success of your gardening.