Water is essential for plant growth, but I see plenty of people get carried away and overwater their crops, doing more harm than good. Not only is water flowing off their gardens, but overwatering can lead to stunted plant growth and disease. 

Being the good environmental stewards that we are, knowing how to manage our irrigation is critical. The first step is allowing water to infiltrate our garden while maximizing the soil’s water-holding capacity. 

We can measure our soil’s water-holding capacity by weighing out 100 grams of dry soil and placing it in a coffee filter in a funnel. Slowly wet the soil by adding 50 ml of water, then add another 150 ml. Let the water drain from the funnel into a jar and measure how much water comes out. 

If 150 ml of water comes out, the soil can hold 25% water (50 ml retained divided by 200 ml poured in). 

Follow these tips to improve your soil and test it again next year. 

• In the desert Southwest, it’s common to plant crops in small depressions so when irrigation comes, it is held near the plant. Terracing and swales are also popular ways to keep water in the field by sloping the land into several flat areas or sunken spots.

• Compaction is counterproductive to infiltration, so don’t work in the garden when the soil is wet and never leave equipment in the field for days. If the garden has been rototilled repeatedly, watch out for sub-soil compaction as the irrigation may seep into the topsoil without reaching the plant roots. Aeration or subsoil tilling with a broadfork may be necessary for better water infiltration. 

• Organic matter is king. Compost or aged manure can hold up to twice its weight in water and act like little sponges in your garden. 

• Mulch helps, too. Studies show that soil mulched with straw can absorb two to four times the amount of water as bare ground. Additionally, mulch reduces soil crusting and softens the impact of rain or sprinklers so that water more gradually infiltrates the soil.

• Lastly, deep-rooted crops also hold more water than shallow roots, so interplanting crops within a row is a great way to take advantage of additional water holding capacity.

THINK ABOUT WINDBREAKS

Since our climate is hot and dry, water evaporates from soil more quickly. Keep in mind plants transpire moisture, too. 

In farming, we call this evapotranspiration (ET)—the water loss occurring from evaporation and transpiration due to temperature, humidity, windspeed and light intensity on any given day. Growers can look up the daily ET and factor in soil texture to calculate the exact number of gallons of water needed for their crops to grow.

Windbreaks like trees and shrubs can help shield plants from light intensity and wind speed. Tucking small plants next to taller crops can help too. Some growers use a misting system to limit transpiration. Others use shade cloth. 

HOW TO WATER RESPONSIBLY

Efficient irrigation is the best way to conserve water. Sprinklers put water into the air— which isn’t where the roots are! Drip tape or weep hose are best as both deliver water directly to the soil. 

Spray stakes have also gained popularity because they can be cracked open early in the season to get the plant growing, then opened fully for mature crops and turned off after the crop is harvested. 

A moisture probe is a sure way to not over- or underwater your crops. Expect to pay $100 for a good one. Anything cheaper is designed for house plants and won’t be accurate enough or have a deep enough probe. Each crop has a preferred moisture range, but a good quality moisture probe can pay for itself in a season.

If tomatoes get too much water, the skins of the fruit crack. Too little and the plant can suck moisture from the fruit, creating blossom end rot. 

The ideal moisture range for tomatoes is 40-70%. When the moisture probe reads 39%, irrigate up to 70% and stop. 

Smart-farming moisture probes can tell the irrigation system when to turn on and off based on the crops being watered. Water consumption can also be monitored on our smart phones, which can save city-water users a lot of money. 

Send your gardening questions to Bryan in care of the BEACON, or email him at [email protected]