With summer in full swing and mother nature beginning to work against the turf, it's a good time to discuss rooting depth and plant stress tolerance on greens. This has been an exceptionally challenging summer so far with more than 8" of rain in the last 6 weeks and saturated turf becoming the norm. The excess water and constant saturated turf conditions, presents many challenges for the grounds staff and the overall health of our greens. We simply have not been able to dry out the rootzones and let the roots breath properly with the continuous rain events and lack of consistent sunshine. The greens remain in fantastic shape this summer, despite the challenging environmental conditions Mother Nature has thrown at us so far.
The rooting depth of Turfgrass plants in a putting green is very important to their overall health and stress tolerance throughout the summer months. The quality of the root systems below ground ultimately dictates the plants overall health and ability to withstand traffic (golfers, mowing, rolling, etc.) on the surface of the green. We spend the majority of the year preparing the rootzones to withstand the harsh summer months, through Aerification, Deep Tining, DryJect, Needle Tining, Topdressing and providing the plants the correct nutrients at the precise times.
Poa & Bentgrass Plant Comparison On Green Surface
The greens here at Gull Lake Country Club were renovated back in 1994 by Art Hills, going from an old style "pushup" native soil greens to sand based rootzones. After the renovation, the greens were seeded with bentgrass but over the years annual bluegrass (Poa) has invaded and pretty much taken over. This is a perfectly normal progression for putting greens in Michigan as Poa is extremely invasive and a very opportunistic plant. We currently have about 40% Bentgrass and 60% Poa.
We are forced to manage two different kinds of grass in our putting greens that have two distinctly different growth habits and nutrient requirements. Poa is much less heat/traffic tolerant compared to Bentgrass. Over the years Michigan State along with many others have provided us superintendents with the knowledge and tools to help Poa battle through the stressful summer months.
In the below pictures you will be able to see the impact this summer has already had on the root structure of both types of plants and the difference in rooting depth of plants virtually next to each other in a green.
Annual Bluegrass (Poa)
The annual bluegrass plants are very tender and fine in texture compared to bentgrass plants as you can see in the above picture. The rooting depth of the Poa is currently 2" - 2.5" on average across the course. While that doesn't seem like much, the root structure that we do have is very white and healthy at this time. During the spring and fall growing season we typically have 3" - 5" roots on all Poa plants and you can really see how the summer stress begins to negatively affect rooting depth.
Bentgrass
Bentgrass thrives in the summer months with very good stress tolerance and fantastic rooting depths. The average rooting depth of bentgrass patches in the greens is between 3" - 4" with beautiful white healthy roots. With the exception of the heat of the summer, bentgrass roots are generally 5+ inches deep.
Take Home Message
Deeper healthier roots allows us to put more stress on the surface with daily maintenance and cultural practices, ultimately resulting in firmer/faster greens. In the heat of a stressful summer, we are basically managing "sod" with the poa plants lack of roots. Its very important to continue to aggressively remove/dilute organic matter within the rootzone. Annual deep tine aerification and routine needle tine venting during the summer months,allows the soil to breath better and rid itself of excess water. With the lack of roots during the heat of the summer, we are forced to do more syringing and cooling of the greens during the afternoons as the top inch of the greens surface dries out. The greens here at Gull Lake Country Club are in wonderful shape and rolling beautiful. The grounds staff will continue trying to stay ahead of Mother Nature as we finish battling though the heat of summer and a wonderful golfing season.
