Ecological ideas

When you hear “native plants,” what comes to mind? Maybe it is the perception that they require less water and fertilizers than non-native landscape plants. Perhaps it is pollinators. Rain gardens? Regardless of whever they bring to mind native plants can be an important greenhouse crop.

Greenhouses are most commonly used to produce ornamental plants that have aesthetic appeal. More recently, we have seen an increase in greenhouse food production, as edible crops gain in popularity. However, there is a third category of crops that can be well-suited for commercial greenhouse crop production — ecological plants. In addition to aesthetic and edible crops, ecological plants are a crop where there may be opportunities for expansion in production.

What are ecological plants? They are crops that are grown that have the intention of serving some purpose beyond simply looking good. It could be to provide habitat for pollinators or a restoration, or maybe a LEED-certified landscape or buffer strips in agricultural fields. For many of these ecological purposes, the materials grown will be native plants.

This article is designed to serve as an introduction to native plant production. While it cannot serve as the complete guide to native plants, it will be an introduction to three important aspects of native plant production that you should consider before planting any crops: use, genetics and propagation.

What will the plants be used for?

First, consider your market. What will the native plants be used for? There are a number of different reasons that native plants are utilized. Restoration and revegetation projects are one of the biggest drivers of the native plant market. These types of projects vary widely, from river bank erosion control to prairie establishment to forest understory rehabilitation. While some of these projects can be accomplished by sowing seed directly into the landscape, there is also a need for containerized plant material.

The type of container and finished plant that are used for restoration and revegetation projects vary widely. For instance, it is not uncommon for herbaceous native perennials to be grown in containers ranging from small plugs and liners up to gallon-sized containers. In fact, smaller finished plants are generally used in favor of large containers. One factor that contributes to this is the planting density at the outplanting site. For many restoration and revegetation projects, a common goal is to establish vegetation and form a plant community that will resist invasive species establishment. The establishment of plantings is usually expedited by using higher planting densities (Fig. 1). If large containers were used for planting, it would not be an economical option.

The other market for containerized native plants is going to be a more traditional landscape market, i.e. quarts and gallons of herbaceous perennials. These plant materials are grown more like traditional ornamental herbaceous perennials because they are used more for projects such as residential or commercial designs that are smaller scale, and perhaps require larger plants for a more instantaneous appeal for ornamental appearances (Fig. 2).

What type of genetics should be used?

What type of genetic material should you use? This can be a large part of the planning and preparation for native plant production. Generally, most people think of native plant genetics as originating from within a specific distance or proximity to the site they will be used. A distance of 100 to 200 miles from the source of the plant genetics (seeds or cuttings) to the outplanting site is common. In some instances, genetics may be collected from the actual site itself; this type of project requires extra planning between clients and producers with a much longer lead time to allow for production.

Many species have a large geographical distribution. When species have a broad distribution, especially across latitudes, it is good to consider provenance when selecting genetics. For some plant species that respond to a certain photoperiod for flowering, dormancy or unique temperature regime, there may be local adaptation to these conditions that may result in different growth outside their location of origin.

Another type of native plant to consider are ‘nativars,’ or cultivars of native plant species. While some may consider nativars to include plants that are the result of two different, but native, species, I tend to only consider them when they are the results of a selection from or cross within a species. This may seem like somewhat of an arbitrary opinion, and this is where cultivated varieties of native species can spark some debate as to whether they are “native” or not. While this debate will not be settled here, it is something to think about.

How should the plants be propagated?

Since there is very limited commercial availability of young native plants (i.e. seeds or rooted cuttings), another consideration you will have to make is propagation methods for your different plant materials. Propagation is linked to genetics in that sexual propagation generally contributes to broader genetic diversity in plant material while vegetative propagation produces clones from the parent stock or material. While some genetic diversity can be maintained when plants are propagated asexually by collecting propagules from a diverse number of individuals within a diverse population or sampling across different populations, this does usually cannot match the amount of diversity that may be captured with seeds.

As a result of the potential for genetic diversity, many native plants are grown from seed. However, vegetative propagation can be very useful when trying to preserve specific genotypes, whether they are nativars or a plant that is challenging to propagate sexually. Aside from the genetics, some propagules are more well-suited to some container types. For small containers produced in high densities, it can be advantageous to use seed, as seedlings are generally smaller than vegetative propagated crops of the same age.

Take-home message

Native plants are crops that greenhouse producers should consider. What new markets might you be able to expand into? If you are interested in producing native plants, simplify your transition by focusing on what exactly you need to produce. First, what are the plants you are growing going to be produced for? Different projects can require very different materials. What type of genetics are appropriate for the project? How will you successfully propagate the species for production? The ecological marketplace provides expanded opportunities for producers as interest in native plants increases.

Christopher (ccurrey@iastate.edu) is an assistant professor of horticulture in the Department of Horticulture at Iowa State University.