Overseeding a lawn, advice & tips

Lawn overseeding is the process of sowing new grass seed into the existing sward on the lawn. In a turf care program there can be numerous reason why a lawn needs overseeding.

Lawns are overseeded for a number of reasons. Lets take a look in more depth at the main reasons for overseeding:

• Repair any bare or weak areas on the lawn - This is arguably the most common reason why overseeding is undertaken. Overseeding the lawn during the correct conditions can help repair and thicken up the sward density on a weak area of turf.
• Change the characteristics of the lawn - Lawns can suffer from a variety of adverse conditions, such as excess shade, extreme drought, wet conditions etc. It is possible to overseed with grasses that will perform better with the inherent conditions of the lawn, thus improving the quality of the lawn.
• Improve the wear tolerance of the lawn - Lawns that receive a lot of traffic through people, machinery etc. can suffer badly with weak grass cover. Overseeding with a hard wearing grass such as Rye grass can vastly improve the wear tolerance of a lawn.
• Encourage a luxury lawn - Maybe your goal is to have a closely mown luxury lawn with a high percentage of fine grasses (bents and fescues).

It can be quite difficult to get new grass seed to establish into an existing lawn for a number of reasons. Initially the seedlings are going to have competition from the existing grasses. The new seedlings also have to cope with the stresses of the current maintenance program, e.g mowing, lawn treatments etc. The weather conditions are not always conducive to successful grass seed establishment.

However there are a few things we can do to tip the balance in our favour and help the seedlings germinate and establish successfully.

• Aerate the lawn prior to overseeding - This task has a couple of benefits for lawn overseeding. Firstly aerating the lawn helps break up any soil compaction. Grass seed will not establish successfully on compacted soils, as the soil will be devoid of air and root development will be restricted. Secondly, lawn aeration creates holes into the soil, this helps the seed come into contact with the soil and helps get the new roots establish.
• Scarify the lawn prior to overseeding - Again scarifying has a couple of key benefits for overseeding. Scarifying removes thatch from the lawn, this is important because new grass will find it difficult establish properly on a lawn with an excessive thatch build up. Scarifying also leaves a nice seed bed, helping the seed come into contact with the soil and improving the chances of successful germination.
• Overseed the lawn at the correct time of the year - Grass seed establishes better if the soil is warm and moist. In the UK the best time of the year for overseeding is late summer or early autumn, when there is still plenty of growth remaining for successful establishment. During this period the soil temperatures will still be high (unlike the spring period). However overseeding during the spring is fine, however the results are unlikely to be good or consistent as during the autumn
  
  It is during this period that the autumn lawn program is carried out, this program also includes aeration, scarifying and top dressing. All of these operations are beneficial for grass seed establishment. It should also be noted after this program has been completed, the lawn will face less disruption and wear and tear from mechanical operations and additional lawn treatments.
• Ensure that there is enough moisture in the soil - It is important that the new seed receives sufficient moisture to help with both germination and establishment.

As we have already mentioned overseeding is best carried out after the lawn has been scarified and aerated. At the very minimum, scarify the lawn or areas of the lawn you intend to overseed, using a spring tine rake if necessary.

Once these tasks have been completed, mow the lawn a little shorter than you would normally. This will help the seed come into contact with root zone and will help with working in the top dressing.

Spread the seed evenly over the lawn (or areas of the lawn you intend to overseed). Using a spreader will yield the best results, however hand spreading is acceptable especially if you are only overseeding localised patches on the lawn. Apply the seed at the manufacturers overseeding rates, this is typically between 10 - 25 g/m.

Once the seed has been applied it needs to carefully worked down into the sward. There are many tools available for this task such as a drag mat, true lute, brush or back of a rake. However if you are top dressing afterwards as recommended, the seed can be worked in with the top dressing, using one of the tools mentioned.

Once the program is complete make sure that the soil receives adequate moisture for the seed to germinate.

Once the seed germinates and the lawn is ready for cutting, raise the height of the mower a touch before mowing. Make sure that the mower is very sharp, this ensures that the grass is cut cleanly. Blunt mower blades do not cut cleanly and damage the grass.

If necessary lightly feed the lawn once the seed has become established. Use a fertiliser suitable for the time of year i.e spring / summer or autumn / winter. When applying fertilisers to lawns it is important apply them evenly and always follow the manufactures instructions to avoid any damage to the lawn.

Fertilisers that have been applied incorrectly can scorch or even kill the grass. This is especially true on new grass. If necessary apply two applications at half rate, leaving a couple of weeks between the initial and secondary treatment.