Planting farm drains helps protect downstream water quality

Restorative planting by Wayne Bennett at Ngaruawahia - about 10 years to create a narrow strip of native bush, free of weeds, a home for wildlife and shelter for stock.

As farm waterways are fenced off to protect downstream water quality, maintenance of those fenced off areas becomes one more issue to deal with.

Planting native plants along these areas is popular but the results can be variable. The benefits from having a site specific design for planting adjacent to farm drains can usually be expected to outweigh the costs.

However, for those who would prefer to do the planting themselves a simple guide is offered.

In order for planting along farm drains to achieve its potential and avoid compromising environmental or production values there are several things to be considered.

1. The planting should be long lived preferably with the potential to self-regenerate.
2. The planting should establish quickly.
3. The project should not affect the maintenance or effectiveness of the farm drains.
4. The species planted should reflect what naturally grows in similar habitats in the same area.
5. The opportunities for weeds to establish in the planted area should be minimised.
6. Species chosen should be either commercially available or able to be specifically produced for the project.

With these considerations in mind a combination of tree and shrub species selected to achieve these objectives is proposed. The range of species is deliberately kept as small as possible.

Understanding the role of each plant is important to those selecting species and placing them in position on the site so here is a brief explanation of the role of each species.

Establishment of tall canopy trees where possible will significantly contribute to the longevity of the project. Totara (Podocarpus totara) is more tolerant of dry and kahikatea (Dacrycarpus dacrydioides) copes better with wet soil.

Two early establishing species are suggested and others with an expected lifespan of less than twenty years are avoided. Kanuka (Kunzea robusta) on drier ground and cabbage tree (Cordyline australis) in wetter areas.

Planting an understorey of shrubs will speed up establishment, help exclude weeds and if the right species are chosen, reflect and protect local character.

For this, a selection of four coprosmas; (Coprosma propinqua, C.rigida, C.rotundifolia, and C.areolata) are proposed. These understorey species will tolerate shade so have the ability to regenerate under taller trees, giving resilience to the project.

There are many understorey shrubs typical of Waikato riparian margins but these species alone, are all quick to establish, tolerate well frosts, drought, flooding, wet feet and wind. Source as many of these four species as possible.

Many native plants not naturally found in this area are commonly planted along waterways and in forest remnants because they are widely available for landscaping purposes. It is good to use the local species to maintain the special local character of this area.

If choosing the right species is essential, arranging them in the most favourable way is also important. Spacing between plants should be between one and two metres. The closer spacing will form a closed canopy more quickly and not need as much maintenance.

Wider spacing will require more weed control until the plants grow and replacement of any losses will be more important but of course the cost of plants will be much less.

The tall trees should be spaced well apart so that they do not compete for sunlight. Due to their size they should also be placed back from the water, but at least a metre from any fences.

Understorey shrubs should be evenly spaced between these trees.

The faster growing colonising species should be planted in between to fill the gaps until the others reach their ultimate size.

With this combination of trees and shrubs most potential weeds will ultimately be shaded out but control of species which can become pasture pests may be needed until this happens.

Otherwise very little maintenance is needed.