STRI Tech Notes - Issue 13 - Spring overseeding advice
Spring success for over seeding
Following the protracted cold winter, with snow lying for weeks on end in some areas, many turf grass swards are looking less than impressive. A weak, open sward, with residual disease scars and heavy infestation of moss, is not uncommon at this time of the year, writes leading sports turf agronomist, Dr Ruth Mann, of STRI.
Therefore, it is time think about preparing for spring and renovating the turf to bring it back to tip-top condition. However, the first thing to note is that this process cannot be rushed - it all depends on the weather producing good growing conditions so the turf surface can heal as quickly as possible. Moss should be controlled at the first available opportunity, with the residual dead matter scarified out of the sward.
Over seeding may be necessary to aid recovery of the turf from disease and renovation work. If the soil temperatures have increased to around 8 - 10 ºC consistently, an application of Primo Maxx should be considered to hold back the top growth of the existing sward, allowing the new seedlings a better chance of establishment.
Research at STRI has shown that applying Primo Maxx five days before a June over sowing operation allowed significantly better seedling establishment in a bent/annual meadow-grass sward. Using Primo Maxx may also allow the height of cut to be raised slightly without affecting playing quality, which will also be beneficial to the establishing seedlings.
We typically see greater success from over sowing with fescue grasses in spring, and fescue/bent mixes in late summer/autumn.
Once seedlings can be seen, it is important to apply some fertility to encourage establishment. Seedlings need a balanced fertiliser to allow root and shoot growth. A liquid fertiliser or seaweed product will allow the seedlings to obtain enough nutrition to encourage strong establishment. Following establishment, Primo Maxx applications will encourage further root development and tillering in the new seedlings.
For most sports turf surfaces organic matter also needs to be managed in the spring, which turf managers may be able to integrate with an over sowing programme. For seed to germinate and establish, it needs to be in direct contact with the soil, which can prove difficult through a layer of thatch; removing this organic matter improves the chance of seedling establishment.
Removal of organic matter can be done by hollow coring or deep scarification, for example with the Graden. The surface impact will depend on the tine or blade size, which should be determined by the amount of organic matter that needs to be removed. The depth of hollow coring or deep scarification should be just below the base of the thatch layer. If organic matter removal is not required, solid tines or verticutting could be used to form a seedbed, depending on seed size and required depth.
Following organic matter removal any holes of slits should be filled with dry sand to dilute the organic matter present and encourage an aerobic rootzone, allowing the beneficial microbes to proliferate and naturally break down thatch. The Graden sand injection unit enables this process in one pass. Depending on the level of organic matter present, the removal process may take longer than one year.
Seed should then be applied. It is important to ensure the seed is worked into the surface to achieve soil contact, rather than sitting in the thatch. This can be done by broadcasting the seed and manually brushing or dragmatting to work the seed in. Alternatively a seeder attachment on the Graden can place the seed directly into the lines where organic matter has been removed. Another option would be a drill seeder, such as the Charterhouse vertiseed, to place the seed directly into the soil profile at the predetermined depth.
Whatever over seeding process is used, and providing the weather has obliged, after a few weeks the new seedlings should have established and management can resume as normal, hopefully on a top quality grass surface free from imperfections!