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MMWD Blog: Think Blue Marin

Welcome to our blog! Written by staff at MMWD, “Think Blue Marin” explores all things water in south and central Marin—water supplies, conservation, new projects, watershed management, and more.

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Apr 20

How Much?

Posted on April 20, 2018 at 10:30 AM by Ann Vallee

by Charlene Burgi

Irrigation season is approaching. When it comes time to turn on your irrigation system, our Weekly Watering Schedule is an amazing tool. It provides guidelines for how much water to apply to the garden based on the current evapotranspiration—or ET—rate. (ET is the amount of water lost into the air through evaporation from soil and transpiration from plants.) The watering recommendations take into account the type of irrigation you are using, as well as if your garden is located in the south, central or north part of MMWD’s service area. It also breaks down watering times for lawns, high-water and low-water-use plants. 

potatoes in plastic tote container
 Potatoes in plastic tote container
But what if you are watering vegetables? What category do they fall into? Do some vegetables need more water than others, or require extra water at certain times of the growth cycle? In general, for watering vegetables you’ll want to follow the “high water use” guidelines in the Weekly Watering Schedule. But as with all gardening, there are many factors that come into play, and so you’ll also want to monitor and adjust if needed to achieve maximum production in your garden. Yes, veggies have microclimates, too!

For example, how well is the soil prepared? Are we talking about hardpan clay with the purchase of a four-inch nursery plant planted in that ground? Or are you planting in well-worked soil with good drainage and optimum sunlight? Is the soil rich in nutrients? Optimum growing conditions along with the recommended amount of water will help you achieve the best results. 

During their growing season, and under good growing conditions, beets, broccoli, Brussel sprouts, tomatoes and carrots will all require about 1-2 gallons of water per week. For a drip system using 2-gallon-per-hour emitters, this would mean about 30-60 minutes of water each week. With these vegetables, it’s best to avoid allowing the soil to dry out. 

Some vegetables require more water, up to 2-3 gallons of water per week. These include cabbage, cauliflower, lettuce and spinach. These are also cool season vegetables and prefer more shade for optimal growth. Because they like similar growing conditions, they make great companion plants. Along with these plants, squash and cucumbers also prefer more water.

Some vegetables need more water during certain periods of their development. Beans and peas need at least two gallons of water per week during their flowering and pod development stages. Corn will need that same amount of water during the time of tassel development and when the kernels begin to swell. Potatoes’ water needs increase to two gallons when the potatoes are the size of marbles. 

Gardening is fun. It can be a challenge or similar to working a puzzle. But for the most part, I have found plants to be forgiving. Enjoy the planning, planting and harvesting. No matter, the reward is the joy when you bite into that first ripe veggie!

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