Grass seed for golf greens

High-quality routine maintenance and renovation must be carried out by experienced greenkeeping staff if a course is to be kept in prime condition.

Golf grass varieties

Plant breeders continue to put greater efforts into the development of new golf grasses and have produced many modern varieties that meet the needs of today’s greenkeepers. A good example of this is the development of the modern Creeping Bentgrass variety, 007 DSB.

This variety retains all the advantages of Creeping bentgrass (high shoot density, prostrate growth, etc) but also has lower fertiliser and water requirements, thereby addressing some of the traditional management issues associated with this species and making Creeping bents an option for a greater number of courses.

Care should be taken to ensure that the varieties in the mixture are well-rated in recognised trials and are of high purity and germination. Time set aside to talk to your local seed representatives and research what is best for you is never wasted.

Golf greens preparation

The golf green is one of the most important areas on a course. It could be argued that a course that gets a reputation for a smooth, fine and even-textured putting surface will be forgiven failings in other areas of the course, whereas a course with great fairways and poor greens will not be granted the same leeway.

Good drainage is important on a green and consists of well-laid clay tiles or plastic pipes usually placed in a herringbone pattern in trenches with adequate falls conforming to a recognised design. The trenches should be backfilled with an approved gravel or stone carpet to a depth of 100mm and a binding layer of sand to a depth of 50 mm spread evenly over the stone. Finally, a good root zone mix that has been laboratory tested should be applied to 250/300 mm depth and a good fine tilth obtained.

Choosing the best golf green grass seed

Traditional fescue/bent mixtures are still the choice of many greenkeepers, and while there is a case for these mixtures where a proportion of fescues and bentgrasses are being maintained within a green, it should be pointed out that there is a paradox in the golf green seed mixture itself. Because of their differing sizes, fescues and bentgrasses should ideally be sown at different depths (10-12 mm for fescues and 2-5 mm for bentgrasses) in order to achieve uniform germination.

There is, therefore, a risk that one or other of the species in a putting green grass mixture is sown either too deep or too shallow. More often it is the more expensive bentgrass component of the seed mixture that gets buried too deep.

Thus, careful consideration should be given to the makeup of one's greens: if a traditional fescue bent mix has been sown for years but only one or other of the species is persisting, then either opt to sow only that species or consider if one is not establishing at all. Increasingly, greenkeepers are opting to sow with 100% of one of the bentgrass species, especially on parkland courses or in instances where mowing heights of down to between 3-4 mm are preventing the persistence of fescues.

The advantage to this golf seeding approach is twofold: firstly, all of the bentgrass seed can be sown at the correct depth of between 2-4mm which ensures a greater chance of a successful establishment of all of the seed.

Secondly, there can also be an economic advantage – typically, bentgrass is more expensive per kilo but if we assume an 18 hole course has 10,000 m² of greens, then at a recommended overseeding rate of 5 g/m² for a pure bentgrass they will need 50 kg, which at £22.50/ kg for a Browntop bentgrass mixture such as AberMajesty equals £1,125. To overseed the same area with a traditional fescue bent mixture such as A11 Golf Greens at a recommended 20 g/m² would require 200 kg, equivalent to ten 20 kg bags costing a total of £1,425.

Overseeding golf courses

Overseeding a golf course with bentgrass cultivars such as AberRoyal and AberRegal is essential to halting the spread of annual meadow grass and improving the visual appearance and disease resistance of hardworking golf greens. With Browntop, Creeping and Velvet bentgrasses to choose from, Germinal has one of the most extensive bentgrass portfolios on the market. To maximise the benefit that these varieties deliver, follow these simple guidelines when planning next season’s overseeding regime.

Planning

Set enough time aside for your golf course overseeding work to be carried out properly and thoroughly. Realistically evaluate what you want to achieve and draw up a schedule of how to get there. Included in this schedule should be an ongoing and comprehensive appraisal of how the bentgrass performs after it has been introduced.

Timing

Throw away the general rule of thumb for overseeding: that it is best carried out in early Autumn. Overseeding can work well whenever the soil temperature is favourable – the perceived minimum soil temperature for bentgrass germination is 10^oC with the optimum range being 16-22^oC. So considering average UK soil temperatures this gives us the range of April – October to work with.

However, increasingly we are seeing benefit from sowing earlier at lower temperatures, an adequate percentage (more than 50%) of some bentgrass cultivars can be seen at temperatures as low as 7.5°c. when weighing up the advantages to seedlings of emerging early in the season when other pressures such as playing pressure are lower, there is a case for sowing earlier as although germination rates are lower, overall seedling mortality can be good.

This range of temperatures typically means that overseeding work in the UK should be carried out between April and September, although in some areas and in some years this season will be extended. Where a comprehensive and efficient irrigation system is in place, it is better to work at the upper end of the optimum soil and air temperature range as this will give better seed establishment and early-stage growth. Alternatively, seeding in advance of warm weather or moisture allows you to utilise a potentially quieter time and then wait for germination.

Frequency

Closely allied to timing is the question of frequency. We all know that sometimes, following a renovation, the planets line up and the weather works in our favour to produce a fantastic result. With that in mind, it can be beneficial to hedge your bets and try to overseed twice or maybe three times in the season. This does not necessarily mean buying twice as much seed: for instance, if you only have the budget to overseed your greens once with pure bentgrasses at 5 g/m², you could split that seed and do two light overseedings, each at 2.5 g/m². One of these treatments could be done early in the season, from late March to early April. As long as this first treatment is followed by a spell of mild weather, the results can be very good and can restore the population of desirable grasses in a green right at the beginning of a busy playing season.

Overseeding more than once does not therefore mean you have to commit to a potentially disruptive full renovation on each occasion: as long as a good root zone is available for new seeds to be sown into, it is feasible to stitch new seed into an established green via linear grooving or even after a light barrel rolling.

Preparation

Evaluate thatch levels, irrigation coverage, wear patterns, drip lines, tree roots and every other possible biotic cause for poor performance of the grasses on your green. This completed – or at least recognised – you are able to proceed with the preparation.

Application: ensure good seed to soil contact

There is no right or wrong way to create the correct environment for germination. Broadcasting or drop seeding into linear grooves, hollow cores or tine holes can all work, and of course, there are many good seed drills available.

The most important thing is to ensure that the seed has good contact with the soil and is sown at the correct depth (not too deeply) and that it remains adequately and consistently moist.

A grass seed only has a small store of energy for the emerging plant to use during the germination period. The coleoptile, therefore, needs to be able to push through the soil surface as quickly as possible so that the first leaf can emerge and begin photosynthesising. The seedling can then start to process its own energy and will be much more able to establish itself strongly.

The correct depth to sow bentgrass to is between 2-5 mm deep. If overseeding takes place following surface disruption – such as hollow coring – it is essential that cores are top-dressed to within 2-5 mm of the surface before either top-dressing or broadcasting seed and then applying a light top dressing of between 2-5 mm.

Watering

Assuming all the points above have been achieved, germination can take as little as seven days – although 14-21 days is more likely. During this period irrigation is really the only controllable resource you have. Ideally, the surface should be permanently damp and as soon as the surface feels dry and no material particles stick to your hand, the surface should be covered with a light sprinkling of water.

Establishment

When seedlings start to appear and the sward is forming, applications of water should become less frequent but heavier. The grass sward should be allowed to dry between applications in order to prevent damping off.

With regards to the first cut, it is an advantage to raise the height of cut. In an ideal world, the cut height would increase up to 6 mm. However, if commitments to play mean the most you can get away with is an increase of 1 mm from your current mowing height (e.g. an increase from a summer mowing height of 3.5 mm up to 4.5 mm) for a period of a week, this would be the next best scenario.

Most often, successful overseeding is thwarted by poor survival rates of new seedlings rather than poor germination. You can be confident that any seed lot you purchase from a reputable source will adhere to minimum germination rates.

The important thing is to consider establishing seedlings within the grass sward during every operation you undertake. Aggressive management of the sward should be avoided while seedlings are becoming established: sensible grooming of the sward – such as brushing and light rolling – and only light aeration if required should be the only management techniques used while the root systems of the new seedlings are becoming established.

A11 Golf Greens Mixture

View A11 The following Bentrgrass Varieties can also be specified:

In recent years, the use of creeping bents on greens and tees has increased as they provide an exceptionally smooth sward. Top-quality cultivars provide good dark colour and are less likely to thatch, having a more upright habit of growth. Creeping bents, if used in well constructed and maintained greens, will give a far better hard-wearing and true putting surface than a traditional fescue/bent mixture. Creeping bent is sown at 8 g/m².

Thatch Control

The accumulation of dead thatch on the surface of a golf green should be avoided as this can quickly build up over a season’s close mowing to create a soft spongy surface. Such a fibre can affect the desirable effects of both drainage and irrigation. Fibre will retain moisture leaving a soft surface that is susceptible to fungal disease. However, when dry, the fibre can act as a water repellent hindering the penetration of moisture to the soil. Under these conditions, grasses such as annual meadow grass will colonise weaker areas when moisture becomes available.

Where there are serious problems of deep thatch, this should be tackled before any overseeding programme is started entertained. Deep coring or verti-cutting followed by topdressing with coarse grain sand is required to punch through and remove the thatch layer and improve the structure of the underlying soil over a period of time. This should be combined with regular, light scarifications throughout the year.

The success of this can be measured over a period of time and should continue until the desired minimum of 1-2mm of thatch is achieved. In order for this to be assessed properly, accurate records need to be kept with the thatch content measured at the beginning of the campaign and measurements taken and recorded on a regular (quarterly) basis to record progress.

Aeration

Soil compaction and the loss of soil porosity leads to a lack of oxygen and moisture in the vital root zone area. This will quickly cause the grasses to die back and thin or bare areas will appear particularly on greens and tees. There are now a large number of automatic machines on the market that are capable of spiking the surface using hollow coring, slitting or solid tines. Solid tines are useful when the ground is very hard and difficult to penetrate.

Slitting tines break up the surface thatch as well as allow the entry of moisture and air into the soil. Where there is serious compaction on a golf green or tee, the greatest effect will probably be achieved by a hollow tining to a depth of at least 100 mm. There are several more spikers on the market that will give an even greater penetration of up to 225 mm. The hole should be filled in with sand of a uniform rounded profile or a good open compost to ameliorate the soil.

Top Dressings

All fine turf areas benefit from a top dressing which will help to preserve a true and level putting surface and reduce the build of thatch. Normally an application of 2 kg/m² is applied two or three times a year during the summer season, although it is important on thin swards not to smother the grasses otherwise dieback will occur.

The type of top dressing to be applied will depend on the original root zone mixture as a similar material should be used so as to maintain a continuity of profile. On well-established golf courses, where the greens were built on local soil, it may well be necessary to apply a top dressing containing high-quality sand, particularly when applied after hollow coring.

For advice on selecting the best golf course grass seed for your greens and fairways, please contact Germinal's amenity experts.