Home Irrigation Primer - Help!

Q. Some advice on watering please. This is my first Las Vegas summer in a new to us house about 12 years old. Lots of lantana, Texas rangers, bottle brush, small short palms and other desert shrubs.  Everything is on a drip systems, no lawn.  I am not sure how often, how long to water.  How many days, once or twice a day, how long each time. My drip are adjustable.

Valve box with valves

A. There are 3 things you need to know to use any irrigation clock or controller; the time of day to water, the days during the week to water and the number of minutes to enter for each station or valve. 

Irrigation controller or timer. Three pieces of information are entered: days of the week on or off, how many minutes to run each valve and the time they begin.

Most drip irrigation systems are a mess because the person who installed them didn't know what they were doing or, if they did, they have been altered over the years by landscape maintenance companies or the owner. You have what you have... unless you are willing to go in and totally redo the system ....which most people aren't.

 

Each colored wire connects to a separate valve. The white one is "common" to each valve as well.

Your irrigation clock requires you to set each irrigation valve separately. Your irrigation system might have lots of different plants on the same irrigation valve. That's very common. If that's the case, you have to find a happy medium for everything on that valve or redo the irrigation system. Most plants are quite adaptable to an irrigation schedule. The biggest plant problems occur when homeowners water daily on everything either because they are lazy or nothing seems to work for them.

 

Irrigation emitters, drippers, should be distributed under the canopy of a plant to supply their roots with water. Lots of emitters are needed to keep large trees upright so they don't fall over.

Time of day. If any part of your irrigation system sprays or "sprinkles" water into the air where the wind can move it around, this should be set for early in the morning and end by sunrise. If it's drip irrigation, it can be done anytime but is usually best if it comes on during the day as it is getting warm and, if a 2nd irrigation is needed that day, to come on late in the afternoon or early evening.

Days of the week. The days of the week depends on how shallow or deep the roots of plants are growing.

Shallow rooted: lawns, vegetables, annual flowers. Daily when it's hot. Vegetables and annual flowers might require a 2nd irrigation later in the day on days it's really hot and windy. Lawns should never require a 2nd irrigation on the same day. If they do, then they should be aerated with a lawn aerator and encouraged to grow their roots deeper.

 

Gasoline driven core aerifier

Rooted to a medium depth: woody shrubs up to 3 to 4 feet tall, woody vines and woody groundcovers. Examples might include roses, lantana, mock orange, etc. Every other day to every 3rd day when it is hot. When it is really hot you might have to irrigate every other day but try to avoid watering daily if possible. Under some circumstances, you might find it necessary.

Deep rooted trees and shrubs: These are trees and large shrubs that provide shade or beauty. Whenever possible, trees and shrubs that originate from desert climates should be on a separate valve. This almost never happens. Examples include Mulberry, Olive, ash trees, Purple leaf Plum, Fruit trees, etc. Once or twice a week during the heat of the summer. In some cases, 3 times a week. When fruit trees are producing fruit they should not be water stressed and require an extra irrigation per week when fruit is being produced. Most landscape trees and shrubs can be water stressed a little bit between irrigations.

Desert trees and shrubs: In an ideal world these should be on a separate irrigation valve but that may happen one out of every 20,000 homes. Examples include Palo Verde, Mesquite, Texas rangers, Texas ebony, cacti but usually not most succulents like aloe and the like. These plans can be irrigated less often than non-desert plants. The volume of water applied to them may be the same as above but more days between irrigations. During the summer they might be irrigated once every 7 to 10 days for instance.

How many minutes for each station = valve. Somehow you have to translate minutes to a volume of water. Also, the volume of water delivered to each plant is dictated by the number and size (gallons per hour) of the drip emitters. 

Here are some general guidelines.

1. Each plant should have a minimum of 2 drip emitters in case one of them fails.

2. Larger plants require more drip emitters. The smallest plants require two drip emitters. Medium-sized plants require four drip emitters. Larger plants/shrubs require 6 - 8 drip emitters. Trees may require 10 – 20 or more drip emitters depending on their size. If other plants are planted close to trees, under their canopy, the trees will require fewer drip emitters because trees are "drinking" from these other emitters.

3. Wet at least half of the area under the canopy of trees and shrubs.

The number of minutes should be enough for water to penetrate at least 18 inches deep in the soil next to the emitters used for large trees and shrubs.  For small and medium shrubs, vines and groundcoveres, 12 inches is deep enough.

Remember there are two types of overwatering: watering too often and watering using too many minutes. It is far worse to overwater the first way than the second.