How Much, and How Often Should I Water My Garden?
If you are here to learn how to work the mysterious dial and buttons and outdated analog screen of your irrigation clock, please take a photo of the make and model, plug that information into a YouTube search prefaced by “how to use a” and once you have figured out how to use the device, return to this blog post. Here, I am going to cover how often and how long you should be watering your yard. Any specific recommendations are based on experience working California’s San Francisco Peninsula (roughly Mountain View to South SF.)
Before jumping into the specifics, an important caveat: Irrigation is, unfortunately, not a “set it and forget it” system. In gardening, there is often what should work and what does work, not to mention that conditions change over time. Plants grow, weather is unexpected. Use the information in this blog as a starting point, but the key is to continue to monitor and make adjustments as needed. In fact, here’s a little gardening secret (and perhaps this applies to many things in life.)
Gardener's Secret: There is no such thing as a green thumb.
Those often mistaken for having a “green thumb” actually just possess a healthy combination of caring, diligence and a willingness to make, and learn from, mistakes. Expert gardeners kill way more plants than the average person. But the second time around, they make better, more informed choices, and this is what makes them "expert."
Step 1: Inspect Irrigation System and Repair as Needed
A beautifully programmed irrigation system will do your yard absolutely no good if the system itself is not functioning properly. Nature is rough and ever-changing, humans are careless, pets and children are clueless, which can all lead to a wide variety of obstructed, broken, poorly performing irrigation systems issues. In defense of all the maintenance gardeners out there, do not hold them solely responsible if the system isn’t working – things happen. However, do hold them responsible if they fail to be observant and if they do not regularly check the system. You or your gardener should be performing a whole-system review annually (at least a month or so before the typical hot weather comes, not 2 weeks into a record heat wave) and regularly monitor for leaks or dry spots.
Check entire irrigation system annually, before hot weather, to identify leaks, blockages and other irrigation shortcomings
This is something your gardener should be able to do. If you’d like guidance or advice and live on the SF Peninsula, feel free to contact us.
Step 2: Identify Zones and Label Them
If you are lucky, your landscape contractor or a former resident left you with a priceless document that is an easy-to-read explanation of which areas (or “zones,” or “stations”) of the yard correspond with the arbitrary numbers assigned by the clock. You might have something that looks like this:
Or if you have a wi-fi controlled clock perhaps it looks like this on your computer or phone screen:
If you are not as lucky, it is worthwhile to take the time to turn on the stations one by one and write down or mark on a paper map the location of the various zones. This becomes immensely helpful when issues arise and you need to adjust “that sunny strip by the driveway that’s always dry.” Instead of turning on all 12 stations to find the right one, you know from your template it is, indeed, Zone 12. I recommend placing this in a plastic sleeve and keeping it in the clock itself if you have a traditional clock (not wi-fi.)
Step 2: Evaluate the Planting
The two most important pieces of information you need for each station are
1) How old are these plants?
2) What are the water needs of these plants?
Age: If you have relatively young plants (less than 1 year in the ground) or are trying to establish a new garden, you will want to water more frequently with less water. Older, established plantings will need longer waterings, but less frequently. This is all based on the size of the roots. Watering a whole stretch of freshly planted 1 gallon plants for 1 hour will be a hearty contribution to the water table (if it’s drip irrigation) while only about 20% of it actually is used by the small and undeveloped rootball. The opposite would be true with larger shrubs. If the roots penetrate deep into the soil (or are trying to), a quick spritz every day will not come close to satisfying their hydration needs, nor will it allow the plant to grow more roots. This can actually limit overall growth.
Same plants, same planting, one year apart. Plants on the left watered 3 days per week for 10 minutes, the plants on the right 2 times per week for 20 minutes.
Water requirements: Are your plants water hungry, or are they drought tolerant? If you're not sure, use this fabulous resource to find out. In California, especially our region, we use irrigation roughly 8 months out of the year when we receive no rainfall. Though some can survive this length of time with no water, all plants will look better with some irrigation, and many will need regular supplemental drenches. Hopefully, all the plants in a particular zone have similar water needs. It is worthwhile to note that plants in containers will need more water than if they are planted in the ground. If a station has a mix of plants with different water needs, for example lavender (low) and roses (high), you have two options.
Option 1: Water to the most thirsty plants. The truth is, although plants are considered “drought tolerant”, this does not always mean that they despise water, per se. If there is good drainage, they should do fine, though you’re “wasting” water, of course. (Some California natives, namely Ceanothus or Fremontedendron species, will die with summer water, so do not follow this guideline if these are in the zone in question. In fact, you should remove the irrigation entirely on these plants once they are established.) Do watch out for soggy soil. This is a sure way to kill all plants, except for ones that grow in bogs. If this is the case, go for option two.
The majority of drought tolerant plants will still perform well with extra water
Option 2: Water to the least thirsty plants, and supplement the thirsty ones with a hose or watering horse. This is much more time consuming and risky if you don’t have a gardener you can trust to do this for you, or if you plan to be out of town for a summer vacation for more than a couple days.
Lawns, which are also technically “plants”, will always fall into the category of frequent, shallow waterings.
Step 3: What type of irrigation do you have
The two basic options are drip or overhead spray. But within those categories, there’s variation. The most important piece of information about the irrigation is the flow rate: how much water will it put out in a given amount of time? This will be a value measured in gallons per minute, or gpm (most overhead spray), or gallons per hour, or gph (most drip emitters.) Below is a chart that features the most common components we use and their respective flow rates, but this by no means covers the extent of what’s out there.
Step 4: Just Tell Me How Long to Water, please!
Ok, now that you understand the logic, I’ve got the easy answer and the hard answer. I’m nice, so I’ll jump to the easy answer first.
If you live on the SF Peninsula, these are the good starting points for scheduling your irrigation clock based on plant type, sun exposure, and irrigation type. The assumption is that this is for “peak water use”, typically July. Most clocks have the option to program monthly, so the watering times should be lower in, say, March, or completely off during the rainy season. This is, unfortunately, not the magic number that works for every property. Monitor and make adjustments as needed for your particular garden’s exposure, microclimate, irrigation efficiency, and drainage.
The number of minutes represents the TOTAL for the week. In most cases (where you’re not doing very deep watering) the total should be broken down into 2 or 3 watering days. Refer back to Step 2 to decide how to break-up the total.
For example, I have a bed of roses (high water) with fixed spray in a full sun exposure, so I’m going to be watering for a weekly total of 46 minutes. They are well established, so I’m going to water twice a week, 23 min each day*.
For the science nerds out there, here’s the hard answer to the question. To calculate the weekly run times using the exact requirements and conditions of your garden, go to this website and follow the instructions. For the weekly ETo, select July. All other months can be calculated as a percentage of your peak (see the chart at the bottom of this post.) Once again, this is still just a starting off point – only careful observation and regular tuning will deliver flawless results. (A smart controller helps, too.)
STEP 5: When To Water
Once you’ve got the total amount of water figured out, there’s still the final step of programming it. This is where that question of long, deep watering vs. short, shallow watering becomes especially relevant (See Step 2).
First, divide your stations into clusters of similar types, which will become your programs. Programs should all have the same type of irrigation. Here’s a simple way to divide your stations:
· Program 1: Lawn
· Program 2: Shrubs & Planted Areas
· Program 3: Containers, Pots, Veggie Garden
Next, choose start times for each program. The best time of day to water is early morning. It’s like putting on sunscreen – apply before it gets hot, instead of doing damage control once the sun is high in the sky. Watering late at night means leaves are wet and more susceptible to disease. Just before the sun is up is the sweet spot. I also suggest watering during times when you’ll be likely to notice the system in action, so you’ll see if anything is leaking or broken.
*HOT TIP: Run fixed spray nozzles for several short bursts, instead of one long run time.
Most fixed spray nozzles put out a lot of water in a short period of time. Water needs time to percolate into the soil, so running this type of irrigation for more than a few minutes will often lead to runoff, especially with clay soils and sloped areas. To avoid wasting water, I recommend multiple run times of 5-7 minutes for each watering day. To use the rose example from above that requires a daily run total of 23 minutes, I’d program the rose zone to run 5:00am for 7 minutes, 6:00am for 7 minutes, and 7:00am for 7 minutes, for each watering day. Leaving an hour between each run time gives the water time to percolate down into the soil. (Yes, I know that only totals 21 minutes, not 23. Lucky for gardeners, the engineering is much more flexible than for other sciences.)
Programs should not be scheduled to run simultaneously. Most properties have irrigation running from a single main line, so having multiple programs running at the same time can alter pressure and interfere with the functioning of the system. Instead, choose different days.
Next comes days of the week. When it comes to a lawn, the best day to water is the day after it is mowed. The worst day to water is the day before it is mowed. People who use
lawns (often families with young children) are most often using them on weekends, so opting for a weekday lawn watering keeps the cleats and frisbees from tearing up the wet grass. For other programs, think about usage. Do you like veggie gardening Sunday mornings? To avoid getting muddy, consider any day other than Sunday. Other than that, pick any day, as long as they’re spaced out evenly.
The best day to water a lawn is the day after it is mowed
Here is a sample irrigation schedule.
If your clock has the capabilities to program individual monthly percentages, you can use these values:
If you’d like to use my template for your own scheduling needs, download it below, or use this link
to download it from Google Docs.