Production of Drought-adapted Intermountain Native Plants Through Low-cost, In-containers for Emerging Western Markets
A comparison of 15 perennial and 10 shrub species under two irrigation regimes, drip and overhead sprinkler with two different growing media, was completed. A masters thesis from the work was written and defended. Based on results showing that sprinkler irrigation and commercial media achieved the best growth, a pot-in-pot production system could recover all investment costs within two years. A follow-up study was started in 2003 comparing conventional above-ground production to in-ground, pot-in-pot production to determine if pot-in-pot is more cost effective than conventional production in terms of growth and number of production cycles during a season.
The goal of this study is to develop a model nursery production system, with an economic analysis, for drought-adapted native woody and herbaceous perennial species using an alternative in-ground container method in the rural Intermountain West (IMW) to encourage adoption by small entrepreneurs. The specific objectives of the project in 2003 are a revision of the original objectives, such that we are investigating whether or not pot-in-pot production of IMW native perennials results in improved growth, thus more production cycles, than conventional above-ground container production.
- 1. The graduate student working on this project, Amy Croft (maiden name Howa), wrote her masters thesis based on the results from 2001 and 2002. These two years of field studies showed that a more expensive organic (composted bark and peat) growing media resulted in significantly greater growth than a locally produced, more inorganic media for most of the species. We found that species native to wetter or higher elevation habitats were particularly affected by the locally produced, lower cost media because the inorganic component, a fired clay that goes under the commercial name of Utelite, is derived from lacustrine sediments that are high in salts that clearly affected salt-sensitive species. We are confident that lower cost local media can be created that is as effective in growing plants as the commercial media. Initial studies show that pumice may be the answer, as it has very low salt levels and is locally abundant.
There were no consistent differences in sprinkler-irrigated versus drip-irrigated plants. Edge rows in the sprinkler plots were often under irrigated due to the effect of wind on the spray pattern. Another disadvantage of sprinkler is that the entire plot area is irrigated, resulting a great deal of wasted water. While growth of the drip-irrigated plants was not consistently different from the sprinkler-irrigated plants, it may have been confounded somewhat by the lack of a subsurface drainage system in the very silty soil in which the study was conducted. Because species were mixed within the study plot for statistical purposes, slower growing species with lower water requirements received much more water that faster growing species with higher water requirements. Thus the slower growing species were exposed to saturated soil longer than would be desirable, due to the slower soil drainage, and their growth may have been affected. Installing subsurface drain pipe would eliminate this problem by allowing excess irrigation water to effectively leach, thus irrigation of drip-irrigated plants would not be affected by wind, and more rapid growth may be realized. However, as the project was set up where drip emitters were punched in for every plant, the sprinkler irrigation is much cheaper to install. Consequently, even if growth of drip-irrigated plants were to be enhanced, it may not be enough to offset the increased installation cost. However, using in-line emitters can substantially reduce installation of drip irrigation. In-line emitters eliminate the labor needed to punch in individual emitters for each plant, and thus, becoming more competitive with sprinklers, could reduce installation costs. Initial studies with in-line emitters showed excellent plant growth. However, because in-line emitters have a fixed spacing, pot installation would require very careful installation to ensure they are aligned with the drip tubing.
Economic analysis of these results showed installing a sprinkler-irrigated, commercial media pot-in-pot production setup to produce Intermountain West native plants could recover all initial costs in two years, and would be profitable over 10 years.
2. Scaling up. Chelsea Nursery in Grand Junction, Colorado, cooperated in scaling up pot-in-pot production to a commercial level. The owners of the nursery chosen were only able to establish three native tree species, bigtooth maple (Acer grandidentatum), mountain mahogany (Cercocarpus ledifolius), and gambel oak (Quercus gambelli). Our original intention was to look at two methods for controlling root circling inside the container: a lining paint impregnated with copper to cause root-tip abortion, and a geo-fabric liner that also causes root-tip abortion, as well as untreated control pots. The experiment was installed in July 2002, and due to a mix up at the time of planting, all control pots, as well as the designated copper-treated pots, were treated with the copper-infused paint, thus we did not have a untreated control. In mid August 2003 shoot elongation and stomatal conductance were measured on all the plants to evaluate treatment effects on growth and photosynthesis. For mahogany, there were no detectable differences in growth and conductance between the copper-lined and fabric liner pot treatments. However, maple growing in the fabric liner treatment had less elongation than those growing in the copper-lined pots, but there were no differences in conductance. This result suggested that the fabric liners negatively affected growth early in the season, possibly by limiting drainage, but that the trees had recovered. Oak growing in fabric liners had substantially reduced shoot elongation, as was stomatal conductance, compared to trees growing in the copper-treated pots. From these results, we are recommending that potential pot-in-pot growers of larger plants use the copper pot treatment, as the fabric liner is somewhat risky, as certain species may be negatively affected. Overall, the growth of the three tree species in the pot-in-pot system with the copper treatment was excellent, far surpassing the growers production with conventional above-ground production to the point that Chelsea Nursery is expanding their area in pot-in-pot production.
We are conducting a followup study with a new graduate student to directly compare pot-in-pot production to conventional above-ground production. Potential nursery entrepreneurs interested in growing Intermountain native plants need this information to make an informed decision as to the most cost effective approach. We have set up a field study comparing the two production systems using three wildflower species, desert 4 o’clock (Mirabilis multiflora), western columbine (Aquilegia caerulea), and palmer penstemon (Penstemon palmeri) in one gallon containers. Each production block consists of 49 plants with two border rows along the W, E, and N sides. The three inner treatment rows consisted of five plants arranged N-S including the southmost plant at the edge of the plot. We chose this approach to evaluate the effect of above-ground exposure on edge plants. Species were randomly assigned to a row, and each paired treatment block was replicated six times. During this first season two production cycles were run, and for each five-week production cycle the graduate student measured total plant water loss once a week by weighing plants at predawn on two consecutive days, root zone temperature once a week, and stomatal conductance one time late in the production cycle. Initial results showed that the above-ground plants had much higher root zone temperature, upwards of 20 C, than those in the pot-in-pot system, with slightly higher water loss and lower conductance. The experiment will be repeated in 2004 with three new species run for three production cycles.
Croft, Amy. 2003. The Production and Native and Adapted Plants for the Intermountain West Using the Pot-in-Pot Nursery Production System. MS Thesis, Utah State University.
Impacts and Contributions/Outcomes
This project is already having an impact, as one of the larger native plant nurseries in Utah, Wildland Nursery in Joseph, is converting production over to pot-in-pot. As mentioned, our collaborator, Chelsea Nursery in Grand Junction, Colorado, is expanding their area of 10-gallon pot-in-pot production. Already the graduate student working on this project, Amy Croft, is planning on starting a native plant nursery, and two other graduate students in the Plants, Soils, and Biometeorology at Utah State University are partnering to also create a native plant nursery. As both nurseries are very influential, we anticipate that they will become opinion leaders to other nurseries and potential nurseries, increasing the production of Intermountain native plants. Since most of this production will occur in rural areas where land is cheaper, the rural economy of the Intermountain West will directly benefit. The results of this study will indirectly benefit the consuming public desiring a naturalized low-water landscape by making Intermountain West native plants more available and affordable. Due to the drought of the past five years, the demand for drought-tolerant plants is exponentially exceeding supply, so the more rapidly these plants can be produced, the more water-conserving landscapes can be installed in the Mountain West.