Species Selection for the Development of a Field Grown Wildflower Sod

Anne Marie Johnson and Ted Whitwell

Department of Horticulture, Clemson University

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In recent years, wildflowers have become a popular choice for providing low maintenance color and diversity in the landscape. However, failure to achieve the desired effect of a wildflower meadow often occurs due to improper seed planting techniques and weed competition. Also, starting a wildflower meadow from seed requires at least two to three years for some perennial species to reach flowering maturity. Having the option of planting a relatively weed free wildflower sod, consisting of established young plants, would eliminate the risks involved in direct seeding and provide the look and color of a mature wildflower meadow in a much shorter time.

There are currently wildflower sod products available comprised of a soil-like media in which young plants are rooted, and it is shipped and planted in the landscape as a solid mat. However, they can be expensive to produce by sod standards, and few species are adapted to southeastern conditions.

The objective of this study was to evaluate 29 annual and perennial wildflower species for potential use in a field grown wildflower sod. Species were selected for evaluation based on the absence of a large taproot, adaptability to the southeastern climate, flowering period, attractiveness of flowers, and potential for survival after root undercutting.

As in turfgrass sod production, aerial shoot growth must be managed to reduce damage to plants when undercut, and to extend the harvesting window. Paclobutrazol (Bonzi), uniconazole (Sumagic), and daminozide (B-Nine) were selected for a preliminary greenhouse evaluation to determine their potential for control of stem elongation in eight of the most promising species used in this study.

Materials and Methods

Planting. All species were evaluated on their ability to withstand the stresses incurred from the undercutting and transplanting process. Fall (7 Oct) and Spring (16 Mar) plantings were done in order to determine optimum planting time for sod survival and harvesting based on appearance and sod stability. Procedures for soil preparation, planting, fertilizing, and irrigating were the same for the two planting times.

The field study location was on the coastal plain region of South Carolina. The research site soil was a Goldsboro fine-loamy, siliceous, thermic Aquic Paleudults. Soil pH was 5.0, 0.0 N -105 P--84 K lbs/A, and 0.8% organic matter. Three months after planting plots received an application of fertilizer at 6.3 N--2.4--9.1 K lbs/A.

The planting area was cleared of existing turf and weeds by a non-selective herbicide application, and deep tilling (5 inches) and fumigated with methyl bromide a month before planting. 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 ft2 plots, separated by buffers. Seeds were lightly raked into the soil to a depth of 0.25 inches, then rolled with a turf roller. To ensure dense plantings, individual species were sown at triple the supplier's suggested seeding rate (Wildseed Farms, Eagle Lake, TX). The experimental design was a randomized block with 4 replications of each species. Each planting date was a separate experiment. Overhead irrigation was used to maintain adequate soil moisture.

Undercutting and Transplanting. Sod undercutting was done at a depth of 2 inches with a Ryan walk-behind sod harvester. Plots planted 7 Oct were undercut 8 Mar, and plots planted 16 Mar were undercut 27 May. To evaluate plant responses to stresses incurred by sod pieces in a retail situation, sod strips were removed from the field and placed on transparent plastic sheeting under overhead irrigation for 7 weeks.

To determine differences between October and March plantings, leaf areas and root weights were taken prior to undercutting. Leaf area readings (cm2) were taken with an LI-3100 area meter. Root samples were collected with a soil auger at a 2 inch depth, and 100 in3 volume.

After 7 weeks on the plastic, wildflower sod pieces were replanted. Seven days after replanting, transplants received an application of fertilizer at 6.3 N--2.4P--9.1 K lbs/A. A final visual appearance rating for fall seeded sod was taken 49 days after replanting and a final appearance rating for spring seeded sod was taken 17 days after replanting.

Wildflower sod pieces were rated on appearance, root density, and sod stability when removed from the field after undercutting, and at the termination of the storage on plastic period. Appearance ratings were based on a scale of 5 = normal size, no damage to top growth, vigorous, healthy appearance, 4 = normal size, slight damage to top growth, vigorous appearance, 3 = normal size, slight damage to top growth, some yellowing of foliage, 2 = undersized, foliage damaged, at least half yellowing and brown, and 1 = undersized, foliage damaged, most foliage and stems yellowing and brown. Plants which were not undercut served as a rating comparison for appearance.

Root density and stability ratings were 5 = no separation, full and solid root growth, 4 = minimal separation, full and solid root growth, 3 = minimal separation, root growth less dense, 2 = minimal matting, slight loss of roots and soil, and 1 = no matting, excessive loss of roots and soil, damage to plants. All ratings were totaled for each species in order to determine species with the best potential and to compare spring and fall plantings.

Plant Growth Regulators . Paclobutrazol (Bonzi, 50 ppm), daminozide (B-Nine, 5,000 ppm), and uniconazole (Sumagic, 25 ppm) were evaluated for efficacy in controlling the top growth of selected species due to excessive damage from sod harvesting equipment. Single applications were applied as foliar sprays (2 quarts/100 square feet) to the following seed propagated, greenhouse grown plants: Achillea millefolium , Chrysanthemum leucanthemum, Coreopsis lanceolata, Coreopsis tinctoria, Gaillardia aristata, Monarda citriodora, Rudbeckia hirta, and Verbena tenuisecta.

Growth index measurements (main stem length from first true leaves to apical tip, plus the distance from leaf tip to leaf tip across the length and width of the pot, / 3) were taken prior to treating and weekly for a month following treatments. Aerial growth was harvested 30 days after growth regulator treatments, then dried at 104F for 3 weeks and weighed.

Results and Discussion

Fall and Spring Planting. After harvesting (undercutting), storage, and replanting, of fall planted and spring planted wildflowers, several species showed potential for further development based on the criteria of surviving undercutting, storage on plastic, and replanting success. Species which did not survive may have died due to excessive damage to aerial growth from the sod harvester, inability to survive simulated nursery stresses, or had poor seedling emergence (Table 1). Plant death from excessive damage to aerial growth was especially common among fall planted species which already had elongated stem and leaf growth by March.

Of the species planted October 1993, and undercut March 1994, Verbena tenuisecta, Achillea millefolium, Coreopsis tinctoria, Rudbeckia hirta, Chrysanthemum leucanthemum, Coreopsis lanceolata, Gaillardia aristata, Monarda citriodora, Oenothera speciosa Nuttall., Silene armeria L., Gaillardia pulchella Foug., Chrysanthemum maximum Ramond, Echinacea purpurea (L.) Moench., and Centaurea cyanus L. survived the undercutting, storage on plastic, and replanting (Table 2).

For October seeded survivors, an increase in ratings of root density and stability occurred from the removal of sod from the field (average rating 3.5) through the storage period (average rating 4.0) (Table 2). Appearance ratings generally decreased from the beginning (average rating 3.8) to the end of the storage period (average rating 2.9) (Table 2). Appearance ratings of replanted species taken 49 days (average rating 3.8) after replanting increased for most species except for the annuals Silene armeria, Gaillardia pulchella, and Centuarea cyanus .

Of the wildflower species planted in March, and undercut in May, Verbena tenuisecta, Achillea millefolium, Coreopsis lanceolata, Monarda citriodora, Coreopsis tinctoria, Gaillardia aristata, and Rudbeckia hirta survived the stress of undercutting, the storage period, and replanting (Table 2). These 7 species rating totals were significantly lower than the maximum rating total of 25.0. The average rating total for all 7 was 12.7 (Table 2).

For March seeded survivors, a decrease in ratings of root density and stability occurred for all 7 species from the time of removal from the field (average rating of 4.4) to the end of storage (average rating of 2.0). Appearance ratings also decreased from the beginning (average rating of 2.2) to the end of the storage period (average rating of 1.9) with the exception of Verbena tenuisecta and Gaillardia aristata (Table 2). Seventeen days after replanting, the average appearance rating was 2.3.

Root weights, density and stability, and appearance ratings for the 7 Oct. planting and the 17 Mar. planting suggest that 7 Oct. was the superior planting date for the maximum number of species surviving harvesting, storage and replanting. Fifty-two percent of the October planted species survived, while only 25% of the March planted species survived. Leaf samples from October (1868 cm2) and March (1554 cm2) (data not shown) were not significantly different (LSD=44.4, P=0.05). However, the total of fresh root weight samples of October planted species when removed from the field was significantly greater at 0.33 lbs than the total of fresh root weight samples of Spring planted species at 0.20 lbs (LSD=2.8, P=0.05). Greater root weights and higher sod density and stability ratings for fall planted species was probably due to a 6 month period for root development as opposed to only a 3 month root development period for spring planted species. Less roots present in spring planted species resulted in the species inability to recover from undercutting and storage stress. Also, warmer temperatures in early June may have further inhibited recovery from undercutting during storage and replanting.

Species Selection. From the results of the spring and fall plantings, several species were selected for wildflower sod development based on two criteria. No single rating of sod density and stability and appearance could be lower than 3.0 and plants had to flower before, during, or after storage. The species that met these criteria were Verbena tenuisecta, Achillea millefolium, Coreopsis tinctoria, Rudbeckia hirta, Chrysanthemum leucanthemum, Coreopsis lanceolata, Gaillardia aristata, and Monarda citriodora. One exception was Chrysanthemum leucanthemum. Though this species had an appearance rating of 2.5 after storage, it was selected due to a high total rating of 20.5 which was statistically similar to the maximum rating of 25 (Table 2).

Plant Growth Regulators. Of the three plant growth regulators, uniconazole had the broadest range of influence over aerial growth of Rudbeckia hirta, Monarda citriodora, Coreopsis lanceolata, and Coreopsis tinctoria. Relatively minor growth suppression was realized with the paclobutrazol and daminozide.

Minimal growth regulator effects observed in this study could be attributed to several factors. Because these plants were propagated from seed, seedling variations could have played a role in plant response. Drench applications of uniconizole and paclobutrazol are more effective than foliar sprays as translocation of the chemical is through the xylem with little translocation via the phloem. Another factor for minimal activity occurring was possibly due to inadequate coverage of the foliar sprays paclobutrazol and uniconazole to stem surfaces.

Optimum species performance seemed to be based on biologically, morphologically and physiologically desirable characteristics that increased the chances of surviving undercutting and resumption of vigorous regrowth when replanted. Root development appears to be the key to producing a sod which holds together well, withstanding the rigors of lifting, storage, and transplanting. Other researchers have looked at the regeneration of Achillea millefolium rhizomes and demonstrated that when released from apical dominance, fragmented rhizomes of Achillea millefolium regenerate rapidly, producing an extensive lateral root system. Others have shown that the high root to shoot ratio of Coreopsis lanceolata may enhance nutrient acquisition and drought resistance in dry, low nutrient environments. These characteristics may make the selected sod species desirable for landscaping purposes requiring adaptability to a broad range of site stresses. Plant life cycles also affected selection. By the end of the storage period spring and summer annuals had gone through the majority of their life cycle and ratings had decreased accordingly.

A fall seeding date was superior to a spring seeding for a spring harvest date. However, if the harvest window and species selection for sod use is to be expanded, control of vegetative top growth will be essential. The plant growth regulator, uniconazole, showed limited control over stem elongation of Rudbeckia hirta, Monarda citriodora, Coreopsis lanceolata, and Coreopsis tinctoria. Other factors such as seeding dates within the fall and winter growing period, will impact root growth and sod success.

A field harvested wildflower sod composed of species adapted to southeastern conditions has potential as a landscape product for low maintenance sites such as highway right-of-ways, land restoration, and erosion control. Growing a wildflower sod comprised of regionally adapted species in a manner similar to that of turfgrass sod, would provide an alternative product for wildflower establishment that is currently not available.

Last Updated 2/1/97