Direct seeding

The technique of direct seeding involves planting seeds where they are to grow, rather than planting them in a pot and transplanting the resulting plant as a seedling. There are many different ways to place the seeds in the field where they are to grow including:

 

  1. Hand planting - the site is prepared with hand implements and the seed is placed by hand or by simple implements onto the soil
  2. Mechanical planting - the seeds are placed by machine into a prepared site, or the machine prepares the site as it plants the seed,
  3. Brush mulching - branches with seeds present (usually as ripe fruits) is cut and laid across a prepared site, where the seeds fall out as the fruit opens, and.
  4. Hydromulching - a slurry of mulch, water, fertiliser and seed is sprayed across bare ground.

Direct seeding is often quick and cheap to carry out and results in very healthy plants with good root development. Its main disadvantages are that it uses a lot of seed compared to tubestock transplanting, can be slow to get results and is difficult to maintain weed-free after seeding.

 

As with natural regeneration, the basic principle is that healthy seed must fall onto bare mineral earth that is moist and warm, then be protected from competition (weeds) and predation until it grows into a mature plant. To achieve bare mineral earth, some form of weed control and soil preparation is necessary, either before, or during, the seeding operation. As for all revegetation, a long weed-free period prior to establishment allows the soil to build up a reserve of soil moisture that the growing plant is able to tap into later. See the chapters on weed control and site preparation for more information.

 

For all direct seeding, it is essential to use healthy seed, with a high level of genetic diversity collected from plants that are well adapted to the conditions at the site of establishment. This means following the basic principles of seed collection and storage that are espoused throughout this site. See the Florabank Florabank Guidelines for more information.

 

 Get the taxonomy right first

  • Make sure you are dealing with the same species/subsp/variety or cultivar
Get the physical and genetic quality right
  • Collect from 20-100 plants.
  • Collect from plants at least 3 plant-heights apart
  • Only collect from large populations or pool multiple collections from smaller populations.
  • Store seed under best conditions from collection right through to use.
 Match the site conditions between collection and planting sites
  • Soil (texture and origin)
  • Altitude
  • Aspect
  • Slope position
  • Latitude (use bioregions as the boundary)
 Then worry about proximity between collection and revegetation sites (local provenance).

 

 

Like all revegetation, maintenance is critical to success. Weeds should be controlled until the plants are well established. Because of the irregular spacing that results from direct seeding, it can be difficult to spray around individual plants, but row sprays, over-sprays with selected herbicides and non-chemical methods can be effective. The developing plants should be protected from grazing until they are large enough to resist the local grazers and browsers. For seeded site, fences built prior to seeding, time-controlled grazing and control of grazer/browser populations are the best options.

 

Hand planting

 

The extensive sugar gum (Eucalyptus cladocalyx) shelterbelts of western Victoria are a great example of what can be achieved by hand direct seeding. In the early part of last century, these sites were ploughed with a mouldboard plough, then seed of sugar gum was broadcast by hand or with hand-cranked seed spreaders. This technique was highly effective before thistles and other weeds became too widespread and is responsible for many thousands of hectares throughout this region.

 

Usually hand seeding is used for small sites, to fill in under existing trees or shrubs (niche seeding), or to add seed to a site primarily established through seedling transplant.

 

Niche seeding

 

A small area (from a few centimetres to a metre in diameter) is prepared before seed is placed on or in the soil. The spots, or niches can be prepared in advance by spot spraying with herbicide (also builds soil moisture) or mulching heavily (old carpet or newspaper is good). Alternatively, a spot can be scalped immediately prior to sowing with a mattock, rake-hoe or spade. At seeding the soil surface can be roughened with a hand tool, to allow seed to be buried or sit on the surface. The seed is sprinkled onto the surface and pushed in with the hand tool or boot. Seeds can be mixed with sand in a jar with holes in the lid (like a salt-shaker), sprinkled by hand or applied using custom-made tools.  After seeding the seed can be watered if necessary and niches can be marked with stakes so they can be located for maintenance and monitoring. A bamboo stake with a strip of plastic tape is good for this purpose. A tree guard could also be placed around the niche to protect the seedlings after germination and to allow shielded spraying for weed control.

 

Broadcasting

 

Also known as 'feeding-the-chooks' for obvious reasons, seed is spread by hand onto previously cultivated ground. The width of the throw should match the width of the prepared site. Sites can be prepared for seeding by long-fallow weed control usually followed by some form of cultivation. Mouldboard ploughing, scarification or rotary hoeing are effective techniques. 

 

Broadcasting results in 'natural' looking revegetation, with no obvious rows of plants. The density of plants can be controlled by mixing the seed with a bulking agent such as coarse sand, chicken pellets or sawdust.

 

For more detailed information on hand direct seeding see the fact sheet produced by Greening Australia.

 

Machine planting

 

For larger areas, a direct seeding machine (direct seeder) can be used to reduce the time taken. There are three main seeder types commonly used:

 

  1. normal agricultural or horticultural machinery,
  2. purpose-built, 3-point linkage seeder,
  3. purpose-built towbar-drawn seeders.

Mechanical seeders usually incorporate weed control, ground preparation, seed application and sometimes seed treatments, water and fertiliser. A typical seeder may have:

  • a disc or blade that 'scalps' the soil (this removes the soil weed seedbank),
  • a tyne or coulter that cuts a slot in the soil,
  • one or more seed boxes to hold the seeds,
  • one or more hoses to deliver the seed to the soil,
  • finger tynes to cover seeds placed in the slot,
  • a press-wheel to firm down the soil and to ensure good contact for seeds placed on the surface.

Mechanical seeder fitted with hopper for applying Wattle Grow and a tank for spraying smokewater.

 

Seeders may also have: multiple tynes; multiple seed boxes; spray equipment to apply residual herbicide to the soil or smokewater to the seed; separate boxes and hoses to apply Wattle Grow (a Bradyrhizobial inoculant); mounding discs; and harrows.

 

Different seeds require different depths of planting for successful germination. Soil moisture is usually more reliable at depth, so if possible it is better to sow seeds a few cm below the surface. Some seeds are unable to germinate at depth as the new shoots are not strong enough to push through the soil to reach the light. Other species, such as Eucalyptus require light for germination and must be sown on the surface. The seeder must be set up so that light requiring species are sown on the surface (and then pressed in with a press wheel) and more robust species are planted at the appropriate depth. This is achieved by having different seed types in separate boxes, and controlling the depth of the scalp and cultivation slot using mechanical or hydraulic adjustments available on the seeder.

 

Some common seeders

 

There are a wide variety of seeding machines in use but not many in commercial production. Many seeders have been designed and built in small quantities in home or small commercial workshops. Some of the seeders listed below are no longer commercially available, but may be available second-hand or for hire or loan. Unless you are doing very large areas of seeding every year, it would be best to hire or borrow a direct seeder, or to purchase one in conjunction with other revegetators through a landcare or farm trees group. Regional organisations should investigate the option of using commercial direct seeding contractors before purchasing their own machinery. Direct seeding is a skilled art, and success is usually dependent on the experience of the operator, especially in marginal years or regions.

 

Machine

Manufacturer/ Designer

Comments

Burford Tree Seeder (formerly known as the Rodden III)

Rod Burford from South Australia.

Burford Seeder website

Saltbush Seeder

David Millsom, Brett Boyd and Bob Cleland Victoria

Sowing saltbush in heavy, saline clays

Rippa Seeder

Barry Stirling, South Australia.

Best machine for rocky, steep sites.

The Hamilton Tree Seeder (now out of production)

Keith Cumming from Hamilton, Victoria.

3 pt linkage, best on basalt soils in high rainfall areas.

Eco Tree Seeder

Richard Weatherly, Mortlake, Victoria

Best on basalt soils in high rainfall areas. Prepares a good seed bed.

Green Tech Tree Seeder

Green Tech Australia, South Australia

Similar to Rodden, but lighter

Kimseed direct seeder

Kimseed machinery, Western Australia.

Kimseed website

 

Shelterbelter

John Cory, Gidgegannup, Western Australia.

 

Mallen Direct Seeder

W. Diamond, Maya, Western Australia.

 

Chatfield Seeder

Denis Chatfield, Tammin, Western Australia.

 

Soil flow seeder

Richard Meyers and Lester Thearle, Gunnedah Research Centre, NSW

2 tyne seeder for trees, shrubs and pasture grasses.

10 tyne units produced and sold in Wellington, NSW

Shelter Seeder

Bill Sharpe, Tasmania

Single-tyne seeder drawn by 4WD motorbike.

 

 

Weed control for direct seeding

 

Scalping is a technique that has proved to be very effective for weed control in direct seeding. After seeding it can be difficult to apply herbicides, so the better the weed control before seeding, the better the long term result. Scalping removes the weed seeds stored in the soil and reduces the number of weeds that germinate after seeding. Scalping can be done either by a separate machine in advance of the seeding, or by a disc or blade on the seeder.

 

Residual herbicides are also commonly used in direct seeding as they confer reasonably good post-seeding weed control for up to 12 months. Residuals are sprayed onto the surface of bare earth, where growing weeds have been sprayed with a 'knockdown' herbicide such as glyphosate. Residuals work by preventing seeds from germinating. Most direct seeders use a tyne or disc to remove the residual herbicide from a small strip on the surface allowing the tree an shrubs seeds being sown to germinate without encountering the herbicide.

 

Herbicides can also be sprayed over the top of the germinating seedlings after sowing, but great caution must be exercised as some herbicides will kill or damage native species. A trial and error approach should be adopted and it is best to discuss oversprays with experienced operators in your district. A trial in WA found that many species tolerated dilute applications of glyphosate and that fluazifop and haloxyfop were tolerated by a wide range of WA species. These herbicides are designed specifically for grass weeds, and will not affect non-grass species that have been sown and will reduce vigorous grass weeds. They are commonly used in agriculture to control grass weeds in non-grass crops. For more information on the appropriate herbicides for use in direct seeding see the Pest Genie website.

 

Brush mulching

 

In this method, branches of trees and shrubs containing ripe fruits are cut and laid across the site to be seeded. Sometimes, just fruits are cut and spread around the site. Sites need to be prepared in a similar way to other seeding methods (weed free, bare earth). This method is commonly used on eroded or degraded sites as the cut branches form a protective layer. They also increase surface roughness and will trap soil, seeds and litter washing across the site. Branch mulching is usually only viable for small sites or for seeding patches in existing native vegetation. It is a very inefficient use of seed, but has advantages when the additional benefits of the rough mulch are needed.

 

It is essential to have a healthy population of the source plants nearby, as many species quickly shed their seeds once cut, so cannot be transported very far. When cutting material from existing plants you must comply with relevant State and Federal legislation. As a guideline, you should remove no more than 20% of the biomass from any one plant.

 

This method also works well for some native grasses such as Themeda australis (kangaroo grass). The whole flowering  stem of the grass is cut and the stems are laid across the ground. Eventually the grass seed releases and drills itself into the soil.

 

Hydromulching

 

In this method, seed is mixed into a slurry with water and a mulch material (such as cellulose or wood or paper pulp) and fertilisers and soil conditioners, then sprayed onto bare soil using a high pressure pump. A binding agent in the mix sets and holds the mulch in place until the seeds germinate and form more permanent cover. This method is commonly used on steeply sloping sites, particularly batters and cuttings associated with civil engineering works. Specialised equipment is required for hydromulching, but there are commercial operators available in most major centres throughout Australia.

 

Further information

Greening Australia has produced a handbook of Revegetation Techniques for Victoria. This book has a chapter specifically on direct seeding. Although written for Victoria it is directly relevant to most of temperate Australia and much of it is also relevant for the whole country.

 

Probably the best and most well known direct seeding manual is Direct seeding of trees and shrubs: A manual for Australian conditions (Dalton, 1993). This book covers a range of issues related to direct seeding: site preparation, seeding methods (hand and machine), timing, weed control, seed treatments, sowing depth, seed coating, mulches, machinery, pests and diseases, maintenance and planning. There are useful tables to help calculate how much seed to use and how to treat different seeds. This book is considered the main text on direct seeding and is widely used as a reference by many people undertaking direct seeding.

 

Two conference proceedings (Greening  Australia Ltd, 1990; Venning, 1985) also set out many of the techniques used in direct seeding, with some regionally specific recommendations included. These conference proceedings include many reports of experiments or monitored direct seeding, with valuable lessons for direct seeders in the successes and failures.

 

Greening Australia Victoria has also produced a series of case studies on different revegetation techniques, called the Footprints fact sheets. Many of these are directly concerned with direct seeding under a variety of conditions.

 

Apart from Victoria, other States have produced books, kits or guidelines for direct seeding, that cover State-specific issues (e.g. (Holt & Bicknell, 1998).  Scheltma (1994) produced general guidelines on direct seeding in WA and specific recommendations for six regions. There are also very good summary notes available as an introduction to the technique in WA (Holt, 1998), Northern Territory (Anon., 2003) and NSW (Curtis, 1998). These publications are likely to be available in the libraries of State agencies or regional organisations.

 

Different species will prefer to germinate at different times of the year. Understanding which species to sow can increase the success of direct seeding. A RIRDC-funded research project has some specific recommendations in this final report.

 

The Australian Journal Ecological Management and Restoration, often features articles and research on direct seeding.

 

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