Even if you don’t live in a drought-prone area, water retention is advantageous for any growing space. Vegetables require copious amounts of water to grow to their ideal eating size, and even in humid climates where moisture is plentiful farms must use surprising amounts of water for irrigation to achieve ideal results.

No matter where you live and grow, there are steps you can take to increase your garden or farm’s capacity for water retention. Ultimately, these management techniques will help you save both resources and time – and your plants will thank you, too. The following are some basic steps you can take to increase water retention. 

Till Less.

Good Heart Farmstead in Worcester, VT uses permanent raised beds for their production, avoiding the use of heavy machinery to till their fields. Each bed must be prepared by broadfork before planting. Photo courtesy of Good Heart Farmstead.

Water retention is directly related to the porous space in a soil’s structure: the more porous the soil, the more capacity it has to retain water. Tilling facilitates lots of temporary porous space in the top layer of soil, but also decimates any soil structure that was in place prior to tilling. Because tilling is achieved with heavy equipment, this repeated compaction actually leads to structural breakdown of soils resulting in a highly dense base soil layer topped by loose soil with no structure – thus, when heavy rains occur, water is more likely to runoff and result in erosion, nutrient loss, flooding, pollution, and, of course, less retained water for future potential drought conditions.

According to the Natural Water Retention Measures project put together by the Environment Directorate General of the European Commission, “Intensive tillage can disturb the soil structure, thus . . . decreasing water retention capacity.” On the other end of the spectrum, “No-till farming (also called zero tillage or direct drilling) is a way of growing crops or pasture from year to year without disturbing the soil through tillage. No-till is an agricultural technique which increases the amount of water that infiltrates into the soil and increases organic matter retention and cycling of nutrients in the soil. The most powerful benefit of no-tillage [sic] is improvement in soil biological fertility, making soils more resilient.”

Many growers choose “low-till” production methods, which involve some precise and timely tillage in combination with cultivation to suppress weed pressure. In these cases, soil disturbance for the purposes of cultivation can be done thoughtfully to avoid compromising the soil structure. Shallow, gentle cultivation of row crops, whether manual or mechanical, can successfully eliminate weed pressure while maintaining healthy soil structure and water retention capacity.

On a commercial scale, decreasing your tillage may be achieved by incorporating some no-till or low-till practices. Careful planning and dialing in the timing of your tillage can also help you decrease the number of times you must till to achieve ideal soil conditions. On a small scale for home gardeners or market gardeners, tillage may be eliminated all together by using innovative tools designed for the small scale like a broadfork or a tilther.

Apply Compost.

Well managed compost piles at Vermont Compost Company in Montpelier, Vermont. Photo courtesy of Vermont Compost Company.

 

In addition to boosting overall fertility and organic matter in your soils, compost itself has an impressive water holding capacity as compared to topsoil. However, because no two composts are created equal, Michigan State University Extension has put together an article that focuses on how to choose composts that increase the soil’s water holding capacity. Before applying any amendment to your soil, it is important to know your key nutrient levels to be able to determine what kind and how much to apply. Just like any other soil amendment, there is such a thing as too much compost.

Check out our blog post on how to master the art of soil nutrients to get a sense of how to balance intuition with science to create an optimal soil nutrient plan, including how to choose annual amendments and incorporate soil building practices.

Increase Your Soils’ Organic Matter.

In 2015, the Natural Resources Defense Council delved into the claim that a “1 percent increase in soil organic matter helps soil hold 20,000 gallons more water per acre” and found that yes, it checks out. Adding organic matter to your soil will help improve its overall structure, giving it healthy porosity and the ability to not only filter water more effectively during periods of heavy rain, but also retain more moisture for plants to access during droughts.

For a crash course in building soil organic matter, check out one of our previous blog posts on the subject.

Consider How and When You Irrigate.

Thoughtful irrigation can go a long way in maximizing your use of this essential resource. The best way to get water directly to the plants’ roots is to use drip irrigation lines that literally drip water onto the soil at the base of the plant. This technique minimizes evaporation and requires less water overall since every drop is going directly into the plants’ roots. Overhead irrigation (i.e. sprinklers) can be appropriate in some instances, like watering in a newly broadcast cover crop – however, overhead irrigation should never be used during the hottest hours of the day, since much of the water will evaporate into the air before it even reaches the soil. Because of the risk of evaporation, all irrigation – even drip irrigation – is best applied in the early morning or evening.

Minimize Bare Soil.

The High Mowing trials field uses annual rye in between beds of peppers and eggplant to minimize the amount of bare soil between their crops. Here, Paul and Taylor are standing on the pathways of annual rye which are mowed periodically for maintenance.

 

When soil is exposed to the sun, the moisture held within the soil will evaporate. If your plants are close enough to each other to throw shade on the areas of bare soil between them, the area of exposed soil can be reduced, saving you water and resulting in fewer weeds. However, when attempting to optimize plant spacing keep in mind that many cash crop plants like tomatoes, peppers and eggplant enjoy some space and need airflow to grow without risk of disease. To retain moisture in the soil between plants that need wide spacing, techniques include using a weed barrier like plastic mulch, landscape fabric, or a biodegradable alternative. Alternatively, sowing dwarf clover or another ground cover that won’t grow tall and compete with the vegetable plant will reduce areas of exposed soil while minimizing weeds at the same time. This is called under-sowing and can help with water retention; before utilizing under-sowing techniques, research the nutrient needs of both your vegetable plant and the ground cover plant to ensure they will not be directly competing with one another for nutrients.

Additional Resources

Natural Water Retention Measures: http://nwrm.eu/measure/no-till-agriculture

Michigan State University Extension’s Study on Adding Compost to Increase Soil Water Holding Capacity: http://msue.anr.msu.edu/news/compost_increases_the_water_holding_capacity_of_droughty_soils

Rodale Institute’s Rainfall Simulator to Compare Soil Health: https://rodaleinstitute.org/rainfall-simulator-compares-soil-health/

Natural Resources Defense Council’s Study on Organic Matter Improving Soil Water Holding Capacity: https://www.nrdc.org/experts/lara-bryant/organic-matter-can-improve-your-soils-water-holding-capacity

Science Advances’ Study on Organic Agriculture: http://advances.sciencemag.org/content/3/3/e1602638

. . . and The Ecologist’s Review of the Study: https://theecologist.org/2017/mar/23/we-need-more-organic-farming