In this article Rob and Jan Fryer, of FuturEcology, provide practical advice on choosing the best plants for riparian margins and on establishing a weed control regime. 

This is part two of a two part series of articles to be published on this website. Part one discusses the reasons why landowners resist riparian planting and how councils can help to resolve these issues. Click here to access the first article.

What types of plants do you recommend being used for riparian planting?

Each site is different so a range of factors need to be considered, such as the questions listed here.

  • Geography — where is the site located and what plants thrive in that ecosystem?
  • Topography — what are the landforms of the site and how do they influence surrounding land use and planting. For example, is it very flat land prone to regular flood inundation?
  • What is the weed burden locally? Are there areas of exotic forest margins that tend to be seed banks for invasive weeds?
  • What will the maintenance regime be and what are the skill levels of the people doing this work?
  • How big is the waterway that we are trying to protect, and what is the particular value we are trying to enhance — is it shading, filtration, enhancing biodiversity (such as whitebait habitat), or a combination of some of these?

Generally each site will have a group of plants that will work well in that area and will do the job for them. There are some great examples around, where low growing plants such as rushes and sedges provide all the attributes we need, due to the small size or shape of the waterway.

We have found people want to plant a “forest”. You don’t get that in a five metre wide riparian margin. Diverse plantings are a nice idea but they are not successful in this context. For example, in Murchison, we planted a riparian margin with 5000 plants, of which 3000 were Carex secta. These are short but wide plants. They provide one metre of shade over a small waterway and will fold down in a flood. We included some taller species amongst them to provide aesthetic appeal. It’s very much “horses for courses”.

In another Murchison project we talked with the Department of Conservation about opportunities to add biodiversity value. The native plant Malecitis flexova is scrubby looking so farmers tend to get rid of it, but it provides great habitat for lizards and fern birds.

The benefits need to be highlighted to the landowner, who can then demonstrate to their community what they’re doing to contribute to New Zealand’s environment.

A riparian planting can be a great opportunity to increase local biodiversity, for example by including threatened species, and by including plants that are naturally occurring in an area. In Nelson, we refer to the Living Heritage planting guide, and are currently involved in a project to return two vanished plant species in the Maitai catchment — it’s simple to grow them and get them back in there as part of riparian planting.

We also plant species which are good for birds where appropriate.

Farmers and other landowners can benefit from a conversation about:

  • what has been here (naturally occurring vegetation in the area)
  • what would work here
  • how to achieve it.

Flood flows also need to be factored in, and this includes keeping flax out and having plants that fold down flat. Hoheria augustifolia is a great riparian species.

What weed control regime do you recommend for landowners?

A rock solid plan and budget for maintenance in the year following planting is vital to the successful establishment of riparian planting. Plant less and look after it better is our motto. There is absolutely no point in committing to planting hundreds or thousands of plants, investing time and money, only to have them swamped by pasture grass in the first spring.

Generally on farms, grass is king. Grass is what makes money, so landowners invest in strong grass species and fertilisers to optimise their growth. These vigorous grass species can easily smother riparian plantings.

That’s why having a clear methodology for the planting is so important. Here’s what we recommend.

  1. Weed-eat the area.
  2. Spray, depending on what’s there. (Perennials need to be dealt with before planting — it’s much easier to do this beforehand. These include: old man’s beard, convovulus, ivy and blackberry.)
  3. Always put a stake beside each plant so you can find it later.
  4. Follow up with maintenance in spring and summer.

At the very least we recommend allowing for follow up maintenance in the spring and summer of no less than three visits from a competent contractor, timed to prevent domination of grass.

The timing of the first visit is critical. This must be done before the first flush of grass in the spring.

In many places we find that our native plants appear to grow strongly at two times of the year — spring and autumn — with little growth over summer and winter. This means we need to time our maintenance regime to ensure plants are unchecked by grass and weeds at these growing times.

With good maintenance in that first year, follow up maintenance is reduced. However, if there is an existing perennial weed problem (with weeds such as blackberry, old man’s beard, gorse or broom) then the site will require ongoing maintenance.

We also note that the farming industry and even councils tend to under-estimate the skills, knowledge and experience needed to complete successful riparian plantings. Although landowners have a close connection with their land and experience in planting various trees and crops, this may not necessarily be helpful with riparian planting.

We recommend that landowners:

  • seek advice from experienced contractors before carrying out riparian plantings
  • be methodical, doing each section of a margin really well before moving on to planting a larger area.