Winter Irrigation Schedule

by Nicole Wires

It is finally beginning to feel like fall. With cooler days here, you’ve likely made the final harvest of your summer plants and have planted your winter garden of peas, broccoli, cauliflower, kale, chard, collards, lettuces, spinach, bok choy, tatsoi, mustards, herbs, garlic, onions, beets, arugula, and so much more!

With the cooler weather and the change in crops, it is time to adjust your irrigation settings to conserve as much water as possible!

Long story short:

The best, most water efficient strategy for your garden now that we’ve had a few heavy rains is to turn your irrigation system off entirely, and to only water when your soil dries out. The top six inches of soil is the active root zone of most of your vegetables. If you are able, come out into your garden every morning to check the soil moisture in this zone. Dig down with a trowel, and touch the soil to see if it feels wet or moist. Grab a handful of soil and make a ball in your hands. If it stays together easily, the soil moisture is sufficient. If not, it is time to water! Run your irrigation system one time for approximately 15–19 minutes, and then turn it off until your soil dries out again.

If you are unable to monitor your garden and its water needs on a regular basis as suggested above, you can set your automatic irrigation system to run once per week for 15–19 minutes, in the morning. Always monitor your soil moisture and plant well-being as much as possible, and if things seem dry increase the number of minutes your irrigation runs. Look for characteristic signs of water stress — extreme signs include wilting, leaves dropping, and plants dying. Less extreme signs are harder to notice. Limited water availability will cause plants to reduce photosynthesis and grow less. Slow plant growth can be caused by many sources (for example nutrient deficiencies and insufficient sun), but if you’ve applied compost and have decent sun exposure, if your plants are still growing very slow they may not be getting enough water. Check the soil moisture more often, or increase your irrigation timing.

If you have a simple egg timer drip irrigation system installed by Planting Justice, you can turn your irrigation off by pressing the off button in the bottom left corner of your timer. You will know your system is off because you will see an icon in the bottom right corner with an image of a valve and a circle and line through it.

Other water saving strategies:

Accompany a reduction in your irrigation schedule with the following regular practices to help your garden thrive with minimal additional water:

  • Regularly add compost to your soil. The organic matter in your compost helps to build the water retention capacity of your soil, encouraging water to stick around longer in the root zone of the soil without running off or seeping through the soil.
  • Mulch over your soil with a 3–4 inch layer of straw to protect your soil from insolation and minimize evaporation directly from you soil.

The nerdy details:

Many different factors determine how much water your vegetable garden needs. Evapotranspiration is the rate of water lost due to evaporation from the soil and transpiration from plants, who take up water through their root zone, and lose water through their stoma when they open them to uptake carbon dioxide as part of the process of photosynthesis. Evapotranspiration rates vary based on temperature, wind, and humidity, which means they vary significantly based on your local climate and the time of year. This handy map shows reference evapotransipiration (evapotranspiration from a short green crop like grass) for different zones across California. For most gardens in the East Bay, you will find yourself in Zone 1 (foggier areas) or Zone 5 (sunnier areas). During the cooler winter months (November through February), average reference evapotranspiration in Zone 1 is approximately 1.04 inches/month, and in Zone 5 average rate is 1.26 inches per month. Most annual vegetables will evapotranspire at rates higher than this reference rate, because they have large leaves and are bigger and taller than grass, so these numbers can be rounded up to 1.5–2 inches/month in foggier/sunnier zones.

This means our gardens need 1.5–2 inches of water (either by rainfall or supplemental irrigation) per month, or 0.4–0.5 inches of water per week, in the winter months.

One inch of water is equivalent to 0.623 gallons of water per square foot. In most our PJ-installed gardens (my garden included!), we use a ¼” drip tape with in-line emitters every 6 inches, which each emit 0.5 gallons of water per hour. It is safe to estimate that in every square foot of your garden, there are at least 2 emitters. Given this, if you were to run your irrigation for a full hour, you would expect to irrigate 1 gallon per square foot.

If your garden is in a foggier zone, and needs only 0.4 inches/week, you’ll want to irrigate for only 9 minutes per week.

0.4 inches x 0.623 gal/sq ft x 1 hour x 60 min = 15 min/week

week 1 inch 1 gal/sq ft 1 hour

If your garden is in a sunnier zone, and needs only 0.39 inches/week, you’ll want to irrigate for only 15 minutes per week.

0.5 inches x 0.623 gal/sq ft x 1 hour x 60 min = 19 min/week

week 1 inch 1 gal/sq ft 1 hour

As you can imagine, with sufficient rains and such low evapotranspiration rates, it is likely to go the entire winter without needed to do much (or any) supplemental irrigation. However, with unpredictable weather and a changing climate, it is always best to monitor your garden and give your plants what they need!

Trust in water.

I have the wisdom of one condemned…
By: Mahmoud Darwish, Palestinian poet
I have the wisdom of one condemned to die,
I possess nothing so nothing can possess me
and have written my will in my own blood:
“O inhabitants of my song: trust in water”
and I sleep pierced and crowned by my tomorrow…
I dreamed the earth’s heart is greater
than its map,
more clear than its mirrors
and my gallows.
I was lost in a white cloud that carried me up high
as if I were a hoopoe
and the wind itself my wings.
At dawn, the call of the night guard
woke me from my dream, from my language:
You will live another death,
so revise your last will,
the hour of execution is postponed again.
I asked: Until when?
He said: Wait till you have died some more.
I said: I possess nothing so nothing can possess me
and have written my will in my own blood:
“O inhabitants of my song: trust in water.”

If you found this post helpful, click the little green heart so more people can find the irrigation answers they need!

Like what you read? Give Planting Justice a round of applause.

From a quick cheer to a standing ovation, clap to show how much you enjoyed this story.