Overseeding a lawn

Overseeding a lawn is an essential task in the lawn care program that is often carried out annually. The optimum time of the year for overseeding a lawn is late summer - early autumn. However overseeding is often undertaken in spring particularly if the lawn has been left thin and weak following moss killing treatment and removal.

Why overseed a lawn

There are numerous reasons for overseeding a lawn including.

• Improve the lawn characteristics - such as shade tolerance, drought tolerance, disease resistance by selecting the correct mixtures for your requirements.

• Repair the lawn - Increase the sward density after renovation has left the lawn looking thin and weak.

• Encourage a harder wearing lawn - that will withstand an increase in traffic and wear and tear.

• Encourage finer grasses - such as bents and fescues if your goal is to have a fine luxury lawn.

Timing of overseeding a lawn

The best time of year to overseed a lawn is during the late summer/early autumn period as part of the autumn renovation program, preferably after scarification and aeration have been carried out. However it is important to do these tasks when there is plenty of growth remaining, this gives the seed time to establish before the onset of winter. It can also be undertaken in the spring time after moss removal, again after scarification has been carried out. However the autumn period is preferred because:

• The soil is warmer in the autumn which encourages better grass seed germination. In the spring the soil temperature can still be quite cold. This period is not always ideal for grass seed to germinate and can lead to very poor results. The last couple of springs are prime examples of this. It has been slow to warm up with very mixed results regarding grass seed germination.

• Generally speaking there is more chance of rainfall and less chance of a drought later in the autumn.

• After the autumn program has been completed the lawn receives little or no maintenance or disruption (such as chemical weed killer applications) which can hinder grass seed establishment.

How to overseed a lawn

Overseeding is best carried out after aeration and (or) scarification as both of these operation encourage the seed to come into contact with the root zone (create a seed bed).

Prior to overseeding mow the lawn a little shorter than normal, this helps the seed make contact with the soil and will also make the following task of top dressing a little easier.

Spread the seed to the lawn, ideally using a spreader (there are many different types that are suitable for this task). Apply the seed at the manufactures recommended rates for overseeding this is usually between 10-25g/m2 depending on the grass seed mixture.

The next task is to top dress the lawn, working it in to the sward with a brush or lute. This will help protect the seed and may also help retain some moisture for the seed.

Overseeding aftercare

To get the best results from your overseeding it is worth noting a few simples points that will help with establishment.

• After the program is complete it is important to keep the soil moist to encourage germination.

• Keep off the area as much as possible.

• If the lawn has not been fed recently it would be beneficial to the new seedlings to apply a suitable feed. Feeding after germination is more beneficial than it is prior to overseeding. Feeding after germination helps reduce the competition from the existing grasses.

• Mow the lawn as normal raising the height of cut a little, just make sure that the blades are sharp so that they cut the grass cleanly (blunt blades tear and pull at the grass causing damage). Allowing the new seedling to grow too long before mowing them puts them under unnecessary stress.

Further tips for successful overseeding

• Soil compaction - New seedlings will find it difficult to establish on a soil suffering from compaction as root development will be impeded, the soil will lack oxygen, drainage will be poor, all to the detriment of seed establishment. This can be remedied by suitable aeration prior to overseeding.

• Excessive Thatch Accumulation - Sowing seed into a layer of thatch is most likely going to yield poor results. Although the grass may well germinate it will find it difficult to establish. Ideally seed needs to be in contact with the root zone for optimum results, this is difficult to do with excessive thatch. If thatch is a problem, a removal program prior to overseeding by scarification would be beneficial. Scarification also leaves a nice seed bed to aid germination.

• Soil temperature - Grass seed needs a warm soil for successful germination, overseeding when the soil temperatures are too low will most likely yield disappointing results. This is the main reason overseeding later in the season is preferred to spring time.

• Soil moisture content - Grass seed needs moisture to germinate and establish. Aim to keep the soil moist, not too wet or too dry.

• Using the correct mechanical operations prior to overseeding - As previously mentioned scarification and to a lesser degree aeration help to create a seed bed which will help with seed germination.

• Choosing the correct grass species for you lawn - It is important the you choose the correct grass seed for your lawn. Although most grasses will germinate, long term establishment may suffer if the grass species does not adapt to your lawn conditions and maintenance program.