Propagation of Colorado Native Plants

SUMMARY

Conditions for the growth of Colorado native plants were determined with the objective of developing methods applicable to the greenhouse and nursery industry and developing generalized methods applicable to native plants.

Germination conditions for over three dozen herbaceous species were determined. It was found that germination rates varied widely for the same species depending on seed source and other factors not determined but probably related to seed viability and dormancy. Protocols for seed germination were determined. Many species responded well to cutting propagation. Procedures for propagation by cutting were developed.

Two woody riparian species were studied, Rhus trilobata and Corylus cornuta.

Results generated showed the need to be flexible in propagating native plants. Methods used one year on one batch of seed may not work the next time they are used. Farmers and growers wishing to grow native plants must be aware of these vagaries and take steps to deal with them in their operations.

OBJECTIVES

The primary objective of this study was to increase the availability of native herbaceous species by generating practical knowledge about how to propagate native plants, grow plants in containers and winter them over.

RESULTS

Most native plants are grown from seed. There is extensive information on germination of seeds of ornamental and native species available in books, journal articles, the internet, government publications and even seed catalogs and suppliers, though sometimes this information is contradictory, which highlights the difficulties of germinating seed caused by their natural dormancy.

Seeds studied for this project exhibited five kinds of dormancy. The first is external or exogenous, where the seed is ready to germinate, but the seed coats are too hard and must be scarified. The second and most common type is endogenous or internal, with the seed embryo fully developed, but requiring some special environmental conditions to germinate. The third type is called double dormancy, being broken by cycles of warm followed by cold stratification. The fourth common type is called secondary dormancy, which can be induced by too high a temperature and can be broken by use of growth regulators or cold stratification. The fifth kind requires seed flats to dry out, either totally or partially, and soak before planting.

As seeding showed true leaves, they were moved no more than once a month to 128 cell plug flats and grown before potting in 32-plug flats or trays with 2 ½ in pots, 32 per tray.

During the spring of 2002, we had an infestation of aphids and during the summer an invasion of thrips as surrounding alfalfa fields were mown. Many native species appear to be very susceptible to these pests in the greenhouse, but do not appear to be bothered by them outside. Native plants, even the smaller sizes, should be placed outside as soon as possible.

Plants grew actively in the summer of 2002, some blooming, and were overwintered in a coldframe that was kept just above freezing. Many broke dormancy early and bloomed in advance of their season in May 2003. Columbine bloomed at the end of March and early Aril and bloomed out by May.

The best results were obtained with a sulfuric acid treatment for 45 minutes.

In our experience, the following plants can be propagated by cutting: agastache, Artemisia, callirhoe invoucrata, oenothera, penstemon, salvia, scutellaria and verbena.

BENEFITS

Native plants are increasingly in demand both for the home gardener and for commercial and municipal landscaping. Native plants are also used in restoration work. Except for wildflower meadows and areas to be restored by mass seeding, plants in pots or plugs are preferred for gardens and landscaping as they establish more quickly. With modest investment for mist benches, hand-seeding equipment and stratification and germination chambers, growers can produce a high-value crop in a small greenhouse. Native plants in Colorado mean low water, low fertilizer and low maintenance to the home gardener. The inclusion of native plants in the landscape can decrease water use and reduce the need for chemical fertilizers.

PRODUCER ADOPTION/REACTION FROM OTHER PRODUCERS

Other growers have shown interest in these results. Some results have already been shared with others informally at meetings and during conversations. A talk was scheduled at ProGreen Expo in Denver, the annual Green Industry Exhibition and Educational Show every January. A short article was submitted to Looseleaf, the monthly Newsletter for the Colorado Nursery and Greenhouse Association. More reactions from others are expected as a result.

CONCLUSIONS AND RECOMMENDATIONS

Farmers and growers wishing to grow native plants as a means of generating more income per square foot can do so relatively easily with a small investment in equipment. Native plants can be grown from seed using a simple protocol.

Obtain seeds from a reputable source. If they are collected from the wild, make sure not to collect more than 10% of any population and be sure to have permission.

The start times may be staggered so that all flats are ready at about the same time. Examine flats undergoing stratification frequently to check if germination has begun early. When roots have extended to the bottom of the plug tray, remove the flats from mist, if used.

OUTREACH AND EDUCATION

An article was published in Looseleaf, along with a paper presented at ProGreen. A poster will be erected at the Fort Collins New Gardens at the Spring Creek Horticultural Center. Discussions are underway with the Colorado Native Plant society to present findings.