Mother Nature Writes A Prescription for Seeding and Renovation Failures In 2016

Posted on October 27, 2016

I cannot remember a late summer when weather extremes hindered so many seeding and renovation efforts.

 In mid-to-late August, thought to be a good time to seed if you have irrigation, resulted in sparse and lackluster seedling growth and vigor.  August was dry (< 0.5” rain) and we experienced above average temperatures in the high 80’s and low 90’s. Conversely, from 18 September to 9 October (about 20 days) there were few periods of sun and for many areas rainfall was in excess of 17”. During    a 7 day period (18-25 Sept.), nights were in the 60’s and low 70’s with extremely high humidity.  On several days, there were torrents of rain ranging from 3 to 5”. In one 48 hour period, over 10” rain came down in torrential sheets in some areas.

 

In renovations (i.e., no-till; no bare ground), the August heat and drought slowed germination and seedlings that had emerged in thatched sites struggled to survive and did not tiller. Subsequent torrents of rain sealed surfaces, causing   seed rot and promoted Pythium blight. Endless days of overcast weather further weakened seedlings and ensured water saturated and oxygen depleted soils. On some sod farms, water inundated fields, and large areas of newly seeded grass were killed. For renovated areas, rain washed dead organic debris in thick suffocating  ribbons.  Dead thatch acted like a gasket, smothering and killing many plants. Living plants struggled to survive and mostly appeared in sparse rows in a state of suspended animation. Long periods of overcast and wet weather also promoted algal growth. Bluegreen algae formed blackish scums on surfaces, usually in low areas were water puddled. Scums rendered soil impregnable to ingress of oxygen and egress of carbon dioxide, and prevented soil drying. 

When renovating areas with thick thatch (usually bentgrass and Kentucky bluegrass) it is essential to physically remove as much organic matter as possible prior to seeding. Vertical cutting units with thick knives are best at ripping through and tearing up thatch. They create deep channels for seed to make contact with soil. On the downside, vertical-cutters remove huge amounts of organic debris, and a nasty, laborious job follows to remove debris and cart it away. For bluegrass lawn renovations, I do not see the same benefits of coring as seen on golf greens where large tines   and close spacing keep holes open for much longer periods. In my view, it is best to devote time and labor to ripping-out dead organic matter with a vertical-cutter versus coring Kentucky bluegrass.  

 Using slicer seeders in heavily thatched areas may not get through to soil surfaces. Severely thatched areas resist penetration and when this happens unit knives run along the top of the surface, and don’t scour or otherwise penetrate thatch significantly. Where operators move too fast the problem becomes more acute and less seed is deposited. Seed placed in and on top of   thatch resulted in few seedlings emerged and those that did struggled to survive. At first the problem was due to heat stress and drought, keeping in mind that the best irrigation system cannot mimic the even distribution and penetration effects of water provided by rain. Later, the problem was compounded by endless periods without sun and excessive wetness. Damping-off pathogens or simply lack of soil aeration made matters worse.  Significant amounts of fertilizer also were trapped in or on top of thatch and did little to help stimulate seedling growth.

Sealed surfaces need to be spiked, sliced, hand-poked with a garden fork, or otherwise disrupted to allow for more rapid soil drying and movement of oxygen and fertilizer into soil.  On renovated lawns with weak or bare areas, a “touch-up” will be needed.  I found a slicer-seeder to be more effective in this situation  since they are far less damaging to existing young plants versus vertical-cutting. However, disks must be adjusted to penetrate through organic mats to open sealed areas and allow seed to make contact with underlying soil. Many sod farmers in our area experienced substantial losses due to rain washed seed and water ponding. Damaged fields will need to be plowed and/or disked and re-seeded.

- Peter H. Dernoeden, Ph.D