Species for Wildflower Seed Production

Anne Marie Johnson and Ted Whitwell
Department of Horticulture, Clemson University

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Large scale wildflower plantings, such as in roadside beautification programs by state transportation departments, are becoming increasingly popular in the southeast. These highway plantings are usually established by direct seeding from seed harvested on site, or more commonly, purchased from growers in the western and southwestern U.S. Western states such as California have a climate conducive to quality seed production, but some species native to the southeast are not successfully grown in these major seed producing areas. For example, Bidens aristosa , a southeastern annual, is not available from any of the large wildflower seed companies, yet this plant is easy to grow in the southeast and is a very attractive roadside wildflower species.

Previous studies have presented information on germination and storage requirements for a limited number of wildflower species that are currently available in the seed trade. There is little information available on seed yields, germination capacities, seed maturation, and harvesting methods for species that may have potential for seed production in the southeast.

The objective of this study was to evaluate 29 wildflower species for commercial seed production in a southeastern environment. Wildflower species were selected for evaluation based on regional performance and potential for wildflower sod production (Johnson and Whitwell, 1994). Production potential for these species was based on seed yield, germination percentage shortly after harvest, and seed maturation rate.

Materials and Methods

Planting . Research plots were located in coastal plain region of South Carolina on a Goldsboro fine-loamy, siliceous, thermic Aquic Paleudults. Soil fertility levels were: pH=5.0, 0.0 N-105 P-84 K-lbs/A, and 0.8% organic matter. The planting area was cleared of existing turf and weeds by a non-selective herbicide application, and deep tilled (5 inches) and fumigated with methyl bromide. In December, plots received an application of 6.3 N-2.4 P-9.1 K lbs/A as a commercial slow-release nitrogen based fertilizer. Overhead irrigation was used during the study to maintain adequate soil moisture.

Seeding date was 7 Oct. Five (summer annuals) of the 29 species were planted the following March to improve establishment. Seedling rates were based on supplier's recommended rates for wildflower meadow establishment (Wildseed Farms of Eagle Lake, TX). Seeds were mixed with contractors sand at 2 parts seed: 1 part sand for even dispersal. Seeds were broadcast using jars with perforated lids onto respective 10.8 ft

Maturation, Harvesting, and Yields . For each species, data were collected for flowering date, seed maturation rate, seed number and weight, dates of optimum seed harvest, and germination percentage. Flowering date was recorded when the first inflorescence opened. Seed maturation was determined by observing the rate at which seeds matured over time. Species seed maturity was based on seed color, seed softness when pinched, and percent of mature seed structures present compared to immature seed structures present. The rating scale was 1=85 to 100% of seeds matured at one time, 2=60 to 84% of seeds matured at one time, 3=seeds matured over a period of weeks, seed heads remained intact until plant senescence, 4=seeds matured and shattered over a period of 2 to 4 weeks, and 5=seeds matured and shattered over a period of 1 to 2 months as inflorescence production continued.

The number of seeds produced was determined by observing the amount and maturation condition of seed-bearing structures present in each plot. Seeds in a square foot area per plot were collected, cleaned and counted, or sub sampled and counted, depending on the number of seeds present. Optimum date of seed harvest was based on maximum amount of mature seed present at a given harvest time. Seeds were stored for two weeks in paper envelopes at 78F at 58% RH to dry before counting. Total seed yields (lbs) were calculated based on seed germination and weight of 100 seeds.

Germination Tests . Seeds were cleaned, counted, and stored in darkness in paper envelopes at 78F at 58% RH. Undersized and green seeds were removed. Seed germination tests were conducted four to six weeks after harvest. Seeds were surface sterilized in a 5% sodium hypochlorate solution followed by three rinses in deionized water. Seeds were placed on moistened Whatman's #5 filter paper in petri dishes and sealed with paraffin wrap. All treatments were exposed to continuous fluorescent light for two weeks at 73F. Following germination tests, remaining seeds were stored in a sealed metal can at 45F and 33 % RH.

Due to poor initial results, a second germination test was conducted for Bidens aristosa . B. aristosa seeds were moist-stratified in damp, whole sphagnum moss and stored in plastic freezer bags inside sealed plastic containers at 45F and 33% RH for 120 days. Seeds were surface sterilized then sown in river sand at a 0.25 inch depth. Flats were placed under mist irrigation for three weeks. Average greenhouse high temperature was 82F and low was 63F.

Results and Discussion

An arbitrary categorization of species potential for commercial seed production was established based on seed maturation rating and percent germination. Germination and seed maturation habits varied from species to species. Species with the highest germination percentages and most even maturation period were Hesperis matronalis , Monarda citriodora , and Silene armeria (Table 1). These species were considered to have excellent seed production potential with seed maturation ratings of 1 or 2 and germination percentages greater than 75% and were given a category I rating.

Species placed in category II had moderate seed production potential based on seed maturation ratings of 1, 2, 3, or 4, and germination percentages between 45% and 75% (Table 1). These species were Bidens aristosa , Centaurea cyanus , Chrysanthemum leucanthemum L ., Coreopsis tinctoria , Gypsophila muralis
, Ipomopsis rubra , and Rudbeckia hirta . Though seed maturation rates varied from 1 (85 to 100 % of species mature at one time) to 4 (seeds mature and shatter over a period of 2 to 4 weeks) in this category, this was considered acceptable for harvesting purposes.

Species placed in category III had low seed production potential with a seed maturation rating of 5 and/or germination lower than 45% (Table 1). Those species were Achillea millefolium L., Coreopsis lanceolata L., Cosmos bipinnatus
Cav., Cosmos sulphureus Cav., Eschscholzia californica Chamisso, Gaillardia aristata Foug., Gaillardia pulchella Foug., Oenothera speciosa Nutall., Papaver rhoeas L., Phlox drummondii
Hook., Salvia coccinea L., and Verbena tenuisecta Briquet. Though several species in this category exhibited determinate flowering and had a seed maturation rating of 1 (85 to 100% of seeds mature at one time), germination percentages were extremely low. These species may require conditions for breaking dormancy other than those provided in this study, such as alternating temperatures and a longer germination period. In addition, species in this category with a maturation rating of 5; the best harvesting date was difficult to determine due to the extended shattering period.

There was no evidence of a correlation between the seed maturation rating and germination percentage.

Species which had acceptable germination for commercial seed production may indicate that seeds were non-dormant at that time and germinated well in moist conditions at 73F in light. Acceptable germination was set at greater than 45% to include native species with potential for production.

Seed yield varied from species to species. Species with the lowest yields were Chrysanthemum leucanthemum at 31 lbs/A, Verbena tenuisecta
at 42 lbs/A, and Papaver rhoeas at 55 lbs/A. Species with the highest yields were Ipomopsis rubra at 5112 lbs/A, Hesperis matronalis at 2658 lbs/A, and Monarda citriodora at 1426 lbs/A. From a seed production standpoint, high yields are desirable. However, low yield species, such as Verbena tenuisecta have potential for seed production because of high retail prices ($85 per lb.).

Several species were eliminated from the study due to poor establishment or insufficient flowers and seed development. Species eliminated from the study were Chrysanthemum maximum Ramond, Echinacea purpurea (L.) Moench., Lobularia maritima (L.) Desv., Oenothera missouriensis Sims, Ratibida columnaris (Sims) D. Don, Rudbeckia amplexicaulis
(Vahl) Cass., and Solidago rugosa Miller.

In a separate study examining seed cleaning techniques and machine harvesting of Silene armeria , Rudbeckia hirta , and Coreopsis tinctoria , machine harvesting resulted in significantly lower yields than hand harvesting. Also, in order to accommodate the variations of seed sizes and weights, adaptations to existing seed cleaning equiptment or specialized equiptment was required.

Results of this evaluation indicate that several species had maturation characteristics and germination percentages suitable for commercial seed production in our southeastern environment. Native species not typically found in the wildflower seed trade, such as Bidens aristosa , also have potential for commercial seed production.

A quality wildflower seed source in the southwest would be advantageous for Departments of Transportation and other organizations requiring wildflowers that are well adapted to regional conditions. A regional seed source would also provide purchasers with southeastern native species less commonly found in the seed trade and more easily grown in the southeast.

Last Updated 2/1/97