Watering – it’s complicated

Like Goldilocks, Kentucky Bluegrass Lawns Need Things Just Right! Not too hot, not too cold, not too dry, not too wet.

The easiest way to describe proper watering is to visualize the “layers” that make up turfgrass and soil; leaves/blades, crown, thatch, stolon, rhizome, root system, topsoil, lower topsoil (6-8″ depth), and subsoil. Focus must be placed to all and not simply to “wet” the surface. Attempts to protect the water bill with frequent, short cycles of watering will almost always cause more harm than good and often it’s better to let the lawn go dormant than to water incorrectly.



To establish deeply rooted turfgrass, irrigate heavily so that water moves past the root system into the lower topsoil. Soil dries from the top down so this drives the roots deeper as the plant’s roots seek moisture deeper in the soil. Keeping the topsoil constantly moist prevents root growth and the turfgrass will become weak and vulnerable. Shallow rooted turfgrass happens when watering is too frequent. Shallow rooted turfgrass will be vulnerable to all types of pressure, particularly drought/heat stress as a trigger to fungal disease. It is best to water turfgrass heavily (deep) but infrequently, allowing leaves and thatch to dry between watering cycles, approximately every third day.

The next variable is the subsoil. Subsoil moisture is much harder to manage because the conditions must be recognized far in advance. Adding difficulty, subsoil moisture levels change so much due to soil type, topography, and seasonal changes. In the spring, the subsoil is usually moist, but moisture levels vary from year to year depending on the climate conditions experienced in the previous year, especially fall and winter. The subsoil helps to protect the topsoil from below, when subsoils are moist there is insulation protecting the topsoil. However, when the subsoil is dry it will be near impossible for water to accumulate in porous soil, like sand, when enduring 90-degree temperatures for more than a couple of days. When speaking of sand, subsoil moisture provides important insulation in terms of temperature. Dry sand gets extremely hot and is the reason why drought stress to sandy soil presents as a significant and pronounced burn to turfgrass, the root system literally gets scorched from this excessive heat. Unless one understands all these variables, this condition is almost always associated with a chemical injury.

Lawns become problematic in the summer season when the subsoil begins to dry. In new lawns (less than 20 years established) it is extremely important to water the turfgrass before it shows stress. Watering should begin in a supplemental fashion as soon as the summer weather patterns begin. If you wait for the turfgrass to show stress before irrigating, it’s already too late! A simple indication that it’s time to begin watering is when depressions in the turfgrass are left when walking across the lawn. If the grass blades do not spring back up but stay compressed, it’s time to water. If you wait for discoloration, it’s too late.

It is extremely important to maintain health and vigor throughout the season, once problems are realized it is often too late for easy correction. Once the subsoil dries it takes so much more water to bring life back to dormant turfgrass. The saturated soil displaces oxygen, and the plants will suffocate. These issues usually correspond with high temperatures in the summer season and fungal disease is almost always the outcome, causing additional injury and requiring expensive fungicide applications and possibly re-seeding to cure. Timing is also important and can either help of hurt turfgrass. Watering should be done in the morning, not at night. Watering in the morning will allow the turfgrass, leaves and thatch, to dry quickly near the surface. Conversely, irrigation in the evening will prevent surface drying and the prolonged wetness coupled with warm summer nights will allow fungal diseases to bloom and spread quickly.

The best practice for watering is to be proactive, begin irrigating before you think you need to. If you are reacting to problems, it will be more costly and take more time to resolve issues. Water heavily to saturate the soil approximately every three days, allowing the topsoil to dry between watering cycles. This will drive the roots deeper into the soil, making the plant stronger and more drought tolerant. Conversely, frequent, short periods of watering will cause shallow roots and compounding problems. Water in the early morning so the surface can dry, preventing additional pressure from fungal disease. Be mindful of microclimates present in your property, recognizing that southern exposures will need water whereas the north side may not. Radiant and reflective heat from structures can be significant and require additional attention. Be mindful of other hard surfaces, especially the ratio of lawn to concrete. Small areas of turfgrass surrounded by concrete (parkways, sidewalks, patios, etc.) will come under stress quickly and will require additional attention. In my experience, most problems in the landscape are preventable without extraordinary effort or chemical/pesticide treatments; an ounce of prevention is worth a pound of cure. Use common sense and appreciate the fact that the modern home lawn is not a natural environment, it’s a harsh, manipulated environment where we humans expect natural things to happen by some miracle.