Colorado has the fourth fastest-growing population in the United States.1 At the same time, Coloradans use 208 gallons of water every day, while the average national per capita water use is 179 gallons per day.2 In Denver, landscape irrigation accounts for 55% of residential water use, and the EPA estimates that more than 50% of water used in outdoor landscapes is wasted due to poor irrigation practices.3,4 Because of the enormous potential for improvement, water conservation programs often target outdoor water use.

Denver Urban Gardens encourages community gardeners to take water conservation into their own hands by watering smarter.

The first step is becoming aware of how we use water and how water is used by the soil and plants. In the vegetable garden, we can follow a few simple guidelines and become experts at reading our plants and environmental indicators so that we use just the right amount of water, no more and no less.

Water when the plants and soil need it, not out of habit.

With the exception of the beginning of the season when young plants and seeds are establishing themselves, vegetable gardens should only need to be watered 2-3 times per week. Even in the heat of summer, gardens do not need to be watered daily. Though it may not be intuitive, we are actually watering the soil, not our plants. Plants absorb water through their roots in the soil, and plant roots grow towards water in the soil. When a gardener provides smaller amounts of water on a frequent basis, the roots have no reason to expand into a strong, expansive system. This practice can be very detrimental to plant growth and is an ineffective use of water. The smarter technique is to water less frequently, but deeper. This practice, especially employed early in the growing season, encourages plants to grow deeper roots that will help them to maintain strength during the hotter, dryer periods later in the growing season.

In the heat of the day, plants may look droopy, and soil often looks dry from the surface. Before going straight to the hose, take a moment to dig into the soil to determine if the buried soil is as dry as the surface. If so, it’s time to water. Before doing so, use a hand tool to lightly break up the crusty surface of the soil between plants so that water can easily penetrate. This can be done on a weekly basis to encourage soil health throughout the season.

Get to know your soil.

Water must first be able to enter the given soil, and then the soil must have the capacity to hold the water so that it is available for the plants. Clay soils are dense which makes it difficult for water to enter the soil. Once water does percolate into the soil, clay soils will hold water much better than sandy soils. Water percolates through sandy soil very quickly, but also dries out faster, so plants will require more frequent watering. Learn more about how to determine what soil texture your garden has here.

Whether you have clay or sandy soil, adding compost breaks up dense clay soils making it easier for water to penetrate and improves the water holding capacity of sandy soils. Soil enriched with compost can result in a 20% decrease in water usage. Add 1-2 inches of compost to the garden in the springtime.

Water by hand.

The EPA estimates that gardeners who water by hand use 33% less water than those who use automated irrigation systems.5 Hand watering allows gardeners to respond to changing soil moisture conditions as watering occurs. For instance, when water begins to pool on the surface, stop watering. Wait for the pool to disappear and then try watering again. If the soil accepts the water, then continue watering until water has penetrated just beyond the root level. You may need to dig around with your hands initially to get a sense of how much water is needed for your soil. This practice uses water more efficiently by getting water into the target area, which reduces fugitive water and is more beneficial to plant health. Be sure to target water towards the soil at the base of the plants, being careful not to water the plant’s foliage.

Reduce water loss.

Evaporation is water loss from the soil surface and transpiration is water loss from the plants’ foliage. To limit evapotranspiration (ET), plan your garden so that the leaves of mature plants are just barely touching. This limits the amount of exposed soil that is susceptible to evaporation. Mulch so that you have little to no soil exposed on the surface. Mulch reduces the amount of soil exposed and in turn reduces the amount of water needed, particularly in sandy soils. Newspapers, straw (my personal favorite), dry grass clippings that have not been treated with chemicals are all relatively inexpensive and free mulch options. As mulch decomposes, it increases the organic content of the soil, which provides a consistent source of nutrients throughout the season. ET is highest during the heat of the day. Watering before 10am or after 6pm allows plants to better access the water provided to them, opposed to the water evaporating before it gets down into the plants’ root zones. Water loss can also occur from loose hose connections. Make sure to tighten your hoses and use o-rings in the base of the hose so that water isn’t dripping unnecessarily. O-rings can fall out of hoses or dry up in our climate, but replacements can be purchased at any hardware store.

So this summer, push your plants to their limits. It will make them stronger in the long run. Water deeply, only 2-3 times each week. Challenge your fellow gardeners to model responsible gardening practices by collectively using as little water as possible. For example, set up a watering schedule for common areas in your community garden so that overwatering does not occur. Water conservation will help your garden have less weeds, lower water bills, and help to maintain a positive image of community gardens across the city. Every drop saved is one more drop saved for a time when we may need it even more than now.

Sources:

1 http://www.census.gov/popest/data/state/totals/2011/index.html

2 http://wwa.colorado.edu/western_water_law/docs/CO_WatandGrowth_NRLC.pdf

3 http://denverwater.org/SupplyPlanning/WaterUse/

4,5 http://www.epa.gov/greenhomes/ConserveWater.htm#landscaping

Click here to read DUG’s general guide on water conservation in gardens.

Click here to return to the Spring 2012 edition of The Underground News.