Overseeding of Cool-Season lawns

In the Auckland City area it is not uncommon for cool-season lawns to look less than perfect after the stress of a hot dry summer.  Disease, drought, weed encroachment heat, poor soil or just plan old neglect may mean that it's time for overseeding.  In the Auckland City area cool-season grasses should be treated almost as though they are hardy at some times and at other times delicate perennials. In other words, to keep a lawn planted to cool-season grasses looking good it will probably need at least some overseeding each year.

The optimum time to overseed cool-season turf grasses in the Auckland City area is during the autumn.  This is when nature establishes cool-season grasses; therefore, the best results with the least amount of work occur at this time.  Do not delay seeding or the grass may not establish sufficiently before winter allowing winter growing weeds to become a problem.  

If you wish to completely eliminate existing vegetation because of large infestations of weeds in particular weed grasses such as Paspalum Species Roundup can be used.  Make sure you complete your last application at least five days prior to seeding. 
Do not use broadleaf weed killers one month before seeding or on new grass until it is well established this will take on average three months. 

Choosing the grass variety to be planted
In the Auckland area the most frequently planted grass planted in full sun situations is perennial Rye grass. Perennial Rye grass (Lolium perenne) is winter growing, winter hardy turf grass capable of withstanding temperature and moisture extremes. During hot, dry periods it tends to become dormant and lose colour. If high quality is desired during the summer period, lawn irrigation is often necessary. Perennial Rye grass performs best in full sun, for shady areas a mixture of perennial Rye and chewings Fescue (Festuca nigrescens) usually give the best results. Bent or common bent (Agrostis capillaris) also known as browntop is to be found in many cool-season grass mixes planted in this region.

Make sure the grass variety chosen meets your lawn's sunlight requirements.  Grass varieties that thrive in full sun may not grow well in part-shade. Shade tolerant grasses may wilt and die in sunny areas.

Preparing the Seedbed
Mow the area to as low as possible without scalping to reduce competition from established grasses.  Short mowing helps prevent the seed from lodging in tall grass and lets light reach the new seedlings.  Use a grass catcher on the mower or sweep up excess clippings.  Do not scalp off all the existing turf - some is needed to protect the germinating seed from wind, hot sun, and heavy rain.

Planting

Fertilizing, Watering and Mowing
Apply a slow release nitrogen fertilizer over the lawn and water it in completely.  To ensure proper germination you will need to keep the seeds moist.  This means watering three to four times daily.  Light, frequent watering will yield the best results.
Perennial Rye will germinate depending on the temperature in approximately 1-3 weeks.  Five weeks after germination, apply a quick release nitrogen fertilizer at a rate of 500g/100 square metres.  Repeat this procedure at six weeks intervals until the lawn is fully established, thereafter follow the recognized fertilizing practice for established lawns.

Mow your new cool-season lawn as soon as it is 70 mm tall with the mower set at 50 mm. Continue to mow at that height until the lawn is well established, thereafter the cutting height can be lowered gradually to between 25 and 40 mm.

The root system of your new turf will continue to grow and strengthen even if the grass blades have virtually stopped growing for the season.  In the spring you will be rewarded with a quick thickening, healthy lawn.