Summer overseeding: Bentgrass can outperform Poa annua
If we purely consider germination, the fact is that if you have a comprehensive, efficient irrigation supply, then the warmer the soil the better. The challenge of summer overseeding is maximising the survival of subsequent seedlings while cutting heights are low and abiotic stress is at its peak.
In the past, this was a barrier to successful summer overseeding. However, the correct selection of species and leading new varieties of bentgrasses coupled with unobtrusive overseeding methods now mean overseeding in summer can be a gamechanger.
For any greenkeepers cutting down to 3mm in summer, it can be challenging to establish new plants. Therefore, you need a variety that can cope with a closer cut, with species selection critical to the success of proactive seeding in summer.
Germinal Creeping bent cultivars 007 DSB and TourPro GDE are bred specifically for close mowing and can establish fast enough to cope with peak season stress. They are also aggressive against Poa annua while it's vulnerable and struggling to colonise a seedbed.
007 DSB has a strong gene pool and adapts to a broad range of climates, even excelling in Siberia and the Middle East. Meanwhile, TourPro GDE scored highest for summer stress and drought tolerance in the NTEP trials and has also thrived in diverse climates. Both plants are also resistant to Dollar Spot, a fungal disease on the rise in the UK. Dollar Spot is encouraged by high humidity, warm days and cool nights.
A chance to outwit Poa annua
At the height of summer, you have the chance to outwit Poa annua. Poa seed germinates most readily at soil temperatures between 10°c and 20°c. Once temperatures exceed 20°c, germination is inhibited quite markedly. Although not applicable to all parts of the UK, July and August soil temperatures in southern counties of England can exceed 20°c in a typical year. Meanwhile, in extremely hot years like 2018, they can rise far higher. Thankfully, you can use this fallibility to your advantage to increase your bentgrass population while Poa is least able to colonise the seedbed.
How to overseed
007 DSB and TourPro GDE can be incorporated into the sward in summer by disc seeding or using a Dynoseeder with two passes of 2.5g/m2 at a depth of 5mm – these methods cause minimal surface disturbance. Pot seeding can also be used by making small holes across the greens to a depth of 5mm before spreading the seed with a drop spreader at 5g/m2. Although slightly more intrusive by requiring sand spread close to the holes after seeding, it’s a useful alternative to disc-seeding equipment. For the best results, choose a time of warm but not unusually high temperatures.
Avoid intrusive maintenance such as verticutting or grooming for a couple of weeks after seeding so the plant roots gain some anchorage. Also, try to relax cutting heights to aid plant survival. Once the plants have established, normal maintenance practices can resume. However, be mindful of any aggressive processes that could impact the plants long-term. While overseeding regularly throughout the year in winter or in spring is beneficial, we recommend a minimum of six weeks between overseeds.
Proactive summer overseeding
Germinal bentgrass seed varieties 007 DSB and TourPro GDE are bred specifically for peak season conditions and can help you overcome colonies of Poa annua. Efficient management decisions at this time can avoid disrupting a hectic peak-season maintenance schedule while securing a great outcome with a sound investment. Try exploring our other helpful golf grass guides.