(Turf Business, June 2008)
At this time of the year seeding without irrigation can be hit or miss. Hot dry spells once the seedlings have sprouted can prove fatal and in addition, this is the time when weeds germinate in profusion. Still, this comment is of no help when this just happens to be the time when new grass cover is to be established. This situation arises due to setbacks in planning and associated construction. There is also the narrow window when football pitches must receive all the renovation possible in time for the new season often barely eight to ten weeks after the end of the last season.
Whether it is a new establishment or over-seeding an existing sward there are a few vital considerations
- Seeding undertaken in a properly prepared seedbed must be adequately covered with soil and/or mulch and rolled to make good contact between seed and soil so as to reduce evaporation losses.
- At least at the time of seeding there should be negligible weed growth – this may necessitate a pre-emergent weed spray with glyphosate.
- Where over-seeding is undertaken the existing grass sward must be severely set back by scarifying so as to reduce early competition with emergent grass seedlings
- A good phosphorus supply should be available in the soil at the time of seeding but nitrogen is more beneficial once there are at least four new leaves in the new growth.
- Any weed spraying immediately the grass seedlings have emerged is in most cases out of the question
While these factors are of concern it is the timing of the operation and the existing soil conditions that will determine the best method to produce the desired results.
Though weed growth can be a major problem with spring and summer seeding, it can be beneficial and cost effective at this time to allow weed germination after soil preparation is complete – and then spray with Glyphosate prior to seeding. The importance of decompacting the subsoil is often disregarded and yet it is essential to encourage rainfall penetration instead of promoting water run-off. Whether broadcasted, drilled or sown with a ‘brillion’ type seeder (incorporating two offset rib-rollers) seed placement and good contact with the soil by rolling remain the vital concerns. In hot dry conditions specialised drilling equipment, able to bury seed deeper below the soil surface, can produce good results. The use of pre-germinated seed with good moisture at this depth can also be worthwhile.
Overseeding into existing cover
Grass swards weakened by disease, overuse, drought or encroachment by foreign species can be over-seeded with success. However, without the opportunity of properly ripping and preparing the seedbed, seed placement must be guaranteed. Without disturbing the existing grass cover, seed must be placed at determined depths. Being an exacting process there are degrees of success with different equipment – some being better able to place the seed at the required depths than others.
With all the sophisticated equipment now available the basic principles in establishment from seed still determine the success of the operation. Besides scarifying to reduce competition from the existing grasses spraying all grass cover with Glyphosate followed by drilling into the dead grass cover can produce the desired result in less time. Developing seedlings must be allowed to develop and not mowed to the desired cutting height of the existing sward. Allowing new growth to develop leaf growth and tiller is vital for proper establishment. Where these essential requirements cannot be achieved the overseeding process becomes a waste of money. A factor often overlooked too is the time needed to achieve the desired result.
The timing of fertiliser treatments too is vital in all overseeding operations. Applied early the response in existing grass cover can quickly dominate and suppress new seedling growth. Left until the seedlings have established, fertilisation becomes far more beneficial to the new growth.
Haste in final soil preparation and seeding is seldom successful particularly in the summer. However, seasonal change can force the issue and make unorthodox methods of seeding productive in limiting situations. Hydromulching on unstable ground enables grass seed to be temporarily protected against rapid water loss from the surface. When no irrigation is available the use of straw mulch as a temporary protection significantly reduces water loss during hot dry weather in the critical establishment period. At the end of the summer the use of germinating netting can add an extra month of warm soil temperatures if not left too late. Grass turfing is only an option if adequate water supply is available two to three times a day in the first critical three weeks. Nevertheless with special care, nutrition and moisture control, newly seeded areas in warm weather develop rapid growth and can be playable within six to nine weeks.
Seeding by whatever means in hot dry summer months can only be successful if a holistic plan is followed. Adequate soil preparation, especially deep ripping of the subsoil, and deep seed placement aid in establishment at this time. Furthermore, the application of high phosphorus prior to seeding, weed control and the promotion of tillering is important. Lifting the mowing height and reducing the frequency also help in reducing water use rate. Failure in providing any one of these conditions will limit the results.