Already established in the US as a proven means of maximising the survival rate of new seedlings on golf courses, fine lawns and other grassed sports surfaces, this method of over-seeding also works in the UK and can help UK greenkeepers to combat the loss of newly established plants as a result of cutting heights being reduced too soon after establishment.

The traditional late-August or early-September ‘renovation week’ is widely accepted as the most appropriate time for UK golf clubs to introduce new cultivars to their greens as a means of out-competing undesirable species such as poa.

While this traditional over-seeding window has its advantages – warm soil temperatures, rapid germination and long daylight hours during which seeding and top-dressing work can be completed – it also has its drawbacks, not least poor survival rates of new plants as a result of cutting heights being reduced soon after new growth has been established.

Cold-seeding addresses this problem by delaying over-seeding until the winter (November to February). Traditionally, UK greenkeepers have been sceptical of this strategy, largely due to the misconception that harsh winter conditions will harm the seed. In fact, the opposite is true: the colder conditions will break the dormancy of fresh seeds by inducing the vernalisation process.

For species such as bentgrasses, which have an in-built period of dormancy after ripening or harvest, this results in excellent germination rates in the early spring with two key advantages: the new plants can mature for several weeks prior to being put under the stress caused by low cutting heights; the newly introduced plants will be able to prosper when the species they are trying to out-compete – notably poa annua – are still lying dormant.

Cold-seeding is also less reliant on irrigation, and the winter freeze-thaw process can help to tuck the seed into the soil where it will vernalise and be ready to germinate upon the arrival of warmer spring conditions.

Proof by trial

Trials carried out by Germinal over the 2017/18 winter proved that putting seed down in November can produce new growth as early as late February or early March, with fresh growth still clearly visible up to eight months later.

Cold seeded with Germinal’s ForeFront Greens mixture in November ’17, a trial at Sweetwoods Park Golf Club in Kent produced its first visible lines of new growth in late-February, with fresh growth still visible in July.

Subsequent trials carried out on golf courses across the UK during the 2018/19 winter supported this evidence with Germinal’s AberMajesty seed mixture responding well to a variety of drilling techniques and seeding timings:

“We disc and dimpled seeded on January 21st and saw the first new seedlings appear as soon as three weeks later. Cold-seeding was very effective, even more so this year given the slightly warmer, settled weather in January. We have been cold-seeding for three years and, despite not using any fungicide in that time, have noticed much less anthracnose in the autumn thanks to reduced sward disturbance in the disease period and stronger, more mature plants being fully established in the sward.”

Peter Roberts, Hart Common Golf Club, Bolton

“We cold-seeded our greens at 5g/m2 using a disc seeder in two directions on 18th February. The first seedlings were visible after eight weeks, and instead of coming through as a lime green colour like they normally would, they were much darker green in colour. We hand-seeded bare areas at the same time and saw new growth just four weeks after sowing. Despite the drilled seed taking longer to establish I was very happy with the results, especially as we had a thick coverage of new growth before the new season got underway.”

Scott Newton, Greenway Hall Golf Club, Stoke-on-Trent

“Cold-seeding our greens in November produced new growth in late-February and provided the benefit of allowing the new plants to establish and mature before lowering to spring cutting heights. Fresh growth throughout the spring and into July helped us to keep our greens in the best possible condition.”

Allan Tait, Sweetwoods Park Golf Club, Edenbridge, Kent