Watering Your Plants in Hot, Dry Summer Conditions

After last year’s record rainfall, it’s hard to believe that this year we’re getting virtually no rain. Watering my poor wilted plants this morning, I remembered that I hadn’t had to get out my garden hose last year. Looking at historical weather data, this is not abnormal. Like many other things in life, time is cyclical.

However, with triple digit temperatures all week and no rain, our plants are definitely suffering. The first line of defense is to use mulch around your plants to prevent evaporation of soil water and to keep the soil cooler around the roots.

Some plants, like vegetables, need more water while others, like succulents and natives, need less. Additionally, the amount of water required by plants varies with the stage of plant growth, temperature, and time of year. Longer, hotter summer days require more water for most plants.

The next line of defense is supplemental watering. The rule of thumb is to apply 1 inch of water per week. The best practice for watering during a drought is to water deeply and less frequently to encourage deep root growth.

Roots are usually found in the top 6 centimeters of soil. Allow the soil to dry out between waterings to prevent shallow roots, weed growth, and fungal diseases. Drip irrigation in garden beds is ideal to help prevent excessive evaporation and deliver water directly to the roots.

How do you know what an inch of water is? Well, it can be a bit complicated and there are many variables. To make it as simple as possible, there are a few things you need to know about your garden hose: the diameter, the PSI rating of the water valve, and the length of the hose. This will help determine the water flow in gallons per minute or gpm.

A typical garden hose flow has an average of 12 to 14, but this can vary. Many garden hoses are 1/2 to 3/4 inch in diameter. The smaller the diameter of the pipe, the lower the gpm it will deliver.

The next thing to consider is the pound per square inch, or psi, which determines the rate at which water passes through the pipe. The average pressure from a household water faucet is around 40 to 60 psi, but can be higher. The last thing to consider is the length of the pipe. As the pipe gets longer and you move the water over greater distances, the flow rate decreases.

To get an estimate, use a 5-gallon bucket and a stopwatch. Open the faucet fully with your hose connected and let the hose run outside the bucket until you are ready to start timing. Start your watch and fill the bucket to the brim. Record the time it takes to fill the bucket.

Let’s say it took 45 seconds to fill our 5 gallon bucket. Take 5 gallons divided by 45 seconds multiplied by 60 seconds (seconds in a minute), and we get 6.66 gpm. This is a rough estimate, but gives you a starting point. You can also find garden hose flow rate calculators online. Try this one from Washington State University at https://bit.ly/3nccAx7.

Another very important factor is when to water. The best times to water are early in the day when temperatures are cooler and at or after sunset. Between 8 p.m. and 6 a.m. is better. As the day gets warmer, water evaporates faster, making watering less efficient.

Lawns may require irrigation up to three times a week, with water penetrating 6 inches deep. Annuals and perennials should be watered twice a week during prolonged droughts. Water these plants long enough to penetrate 8 inches into the soil. For shrubs, irrigate twice a week, getting 12 to 16 inches of moisture, and trees once a week at a depth of 18 to 24 inches. Use a long screwdriver to test the depth of water movement in the soil.

Don’t worry if your lawn begins to sleep in excessive heat. Most lawns can survive two to three weeks of dormancy and will green again as temperatures cool and the rains return. You could enjoy the mowing break.

One way to combat future weather extremes – whether drought or excessive rain – is to choose native plants that are tolerant of our climatic fluctuations. They can handle it better than highly grown plants. Keep them zoned into special spaces to limit the area you need to water.