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Bulbs in turfgrass Research examines performance

Bulbs in turfgrass

Research examines performance

by Bodie Pennisi and Clint Waltz, University of Georgia, and William Miller, Cornell University

Spring-flowering bulbs are routinely planted in flower beds for dramatic display of earlyseason color, but what if you could grow them in turfgrass? Studies have indicated that spring bulbs can grow in competitive warm-season turfgrasses and serve as an earlyseason floral resource.

Flowering bulbs have been known to naturalize and become perennial in grassy meadows and pastures, but they must compete successfully with the predominant vegetative cover. While previous studies have shown success in northern latitudes, knowledge has been lacking for bulb growth in more southern climates... until now.

For the purposes of this study, “bulbs” are considered herbaceous geophyte species with foliage and flowers aboveground and an underground structure, the ‘bulb,’ which persist belowground.

We undertook this research study to: 1) determine which species and cultivars can perennialize in a subtropical climate, 2) evaluate which species and cultivars can sustain acceptable growth and flowering performance under standard turf maintenance practices of weed control and mowing schedules, and 3) compare bulb performance in warm-season and cool-season turfgrasses.

The turfgrasses

Plantings were established at the University of Georgia campus in Griffin, Georgia. We studied geophyte performance in two turfgrasses: hybrid bermudagrass ‘Tift 94’ (TifSport®) and the tall fescue, ‘Lexington’. These were chosen for growing season and habit (hybrid bermudagrass is considered a dense, creeping, warm-season grass, whereas tall fescue is considered a slower-growing bunch grass grown during the cool season).

Although tall fescue is considered generally less aggressive, its peak growth would coincide with bulb flowering and thus could potentially be even more competitive than hybrid bermudagrass.

The bulbs

The main criteria in selecting the bulb species was suitability for culture in a subtropical climate and a bloom period that would be completed by April or early May before mowing was resumed. The following bulb species and cultivars were used: Chionodoxa sp. ‘Blue Giant’ (glory-of-the-snow), Crocus tommasinianus ‘Ruby Giant’ (crocus), Crocus

vernus ‘Remembrance’ (crocus), Narcissus ‘Ice Follies’, N. ‘Tete-a-Tete’, N. ‘Thalia’ (daffodil), Muscari sp. ‘Blue Magic’ (grape hyacinth), and Scilla sybirica (Siberian squill).

Planting

The bulbs were planted on December 5, 2018 in wellestablished full sun, turf plots in the following manner: 4A tractor-drawn bulb planter cut a 0.5-meter wide strip by incising the top 4-5-cm of turf, root, and soil layer, the turf was rolled back and bulbs were placed manually on the soil bed leaving approximately 5 cm between individual bulbs. 472 smaller bulbs (Scilla, Muscari, Chionodoxa) or 21 larger-sized bulbs (Narcissus) were arranged in a space measuring approx. 40 x 100 cm. 4Turf was rolled back to cover the bulbs and smoothed with a riding roller. 4There was 30 cm of buffer space separating the bulb entry/treatment combination.

Mowing

Mowing initiation dates in 2019 were the following: 4 4 Tall fescue: April 1, April 17, May 1, and May 15 Hybrid bermudagrass: May 1 and May 15

Mowing height of both turfgrasses was 7.5 cm and areas were mowed with a rotary mower and clippings returned. Mowing dates and height were chosen as a compromise between allowing bulbs to grow undisturbed and maintaining reasonable aesthetic appearance in the lawn. Mowing was done perpendicular to the planting strips, which the bulb planter had cut into the turf.

Fertilization

The turf areas were fertilized with a 16N-1.8P-6.6K granular material applied monthly at 49 kg ha-1. Hybrid bermudagrass plots were fertilized in May, June, July, and August. Tall fescue was fertilized September, October, March, and April.

Irrigation

In the absence of rainfall, plots were irrigated during the growing season to supply 2.54 cm of water per week to prevent drought stress.

Data collection

We were primarily interested in bulb performance and persistence over a two-year period (2019-2020). Each treatment was evaluated for first flowering date, flowering abundance (number of bulbs with flowers, expressed as percent of planted bulbs, the first year after planting), and total number of blooms (second year after planting). We considered satisfactory persistence as >40% bulbs with flowers after two growing seasons, and nonpersistence as <10% bulbs with flowers after two growing seasons. Data collection comprised of weekly counts of flower emergence, and number of blooms. Due to increased bulb foliage leading to thickened canopy in 2020, it was difficult to identify which bulb had produced a bloom, or which bloom belonged to which bulb, therefore we counted total blooms per 40 x 100 cm space where bulbs had been planted. Additionally, some bulbs produced multiple blooms (i.e. daffodil ‘Tete-a-Tete’, and ‘Thalia’). Therefore, we performed statistical analysis separately on two groups of bulbs, the first group containing the three daffodil cultivars, and a second group containing the remaining bulbs entries. We were also interested in turf recovery after using the bulb planter and visually assessed turf health. Data from 2020 were analyzed separately for tall fescue and hybrid bermudagrass because the mowing treatments were different and therefore could not be directly compared.

Results and discussion

After planting in December 2018, all but one of the bulb species emerged in mid-January 2019 in both hybrid bermudagrass and tall fescue. > Daffodil ‘Tete-a-Tete’ and crocus ‘Ruby Giant’ and

‘Remembrance’ exhibited earliest flower emergence in both types of turfgrass. > Siberian squill and daffodil ‘Ice Follies’ flowered by mid-February. > Daffodil ‘Thalia’, grape hyacinth, and glory-of-thesnow first bloom appeared beginning of March. All bulbs flowered within a few days in tall fescue and hybrid bermudagrass in 2019. Similar patterns were observed in 2020 although the flowering was somewhat delayed, except for Siberian squill which bloomed 1012 days earlier (tall fescue, or hybrid bermudagrass, respectively). All bulbs tested flowered over three

Best flowering bulbs in 2019, grape hyacinth (A, tall fescue, B, hybrid bermudagrass) and daffodil ‘Thalia’ (C, tall fescue, D, hybrid bermudagrass). Photos taken March 13, 2019.

weeks, with peak bloom from last week of February until mid-March.

Significant differences in bulb performance among

species were detected the first year after planting. Only grape hyacinth and daffodil ‘Tete-a-Tete’ showed higher than 50% flowering, with grape hyacinth having the highest number (63.4% and 60.5%, in tall fescue and hybrid bermudagrass, respectively).

Analysis also indicated significant differences in

bulb performance between the two turfgrass types

(tall fescue, 31.9% emergence, hybrid bermudagrass, 35.1%). Except for grape hyacinth and daffodil ‘Ice Follies’, the remaining bulb entries had higher percent flowering in hybrid bermudagrass as compared to tall fescue.

Mowing treatment did not significantly affect total

number of blooms; however, different bulb species showed significant differences in bloom counts. Since the mowing treatments imposed were not identical, direct comparison between bulb performance in tall fescue and hybrid bermudagrass could not be made. Daffodil ‘Tete-a-Tete’ in the large-bulb group and crocus ‘Ruby Giant’ in the small bulb group, had by far the highest numbers of blooms in tall fescue. ‘Tetea-Tete’ and ‘Thalia’ in the daffodil group and crocus ‘Ruby Giant’ in the small bulb group, had the highest numbers of blooms in hybrid bermudagrass. It is worth noting that daffodil ‘Tete-a-Tete’ produced on average of two blooms per planted bulb in both turfgrass lawns.

Following planting, all of the bulb species exhibited

remarkably similar first flowering in both

turfgrasses. However, only daffodil ‘Tete-a-Tete’ and crocus ‘Ruby Giant’ exhibited satisfactory persistence (defined as >40% bulbs with flowers after two growing seasons), although daffodil ‘Thalia’ showed satisfactory persistence in hybrid bermudagrass lawn. Based on our results, daffodil ‘Ice Follies’, Siberian squill, grape hyacinth, and glory-of-the-snow were non-persistent (defined as <10% bulbs with flowers after two growing seasons). Grape hyacinth’s performance is surprising because anecdotal evidence and numerous reports have indicated that it has excellent perennialization in Georgia, including nonmanaged grass areas on University of Georgia’s Griffin campus. It also worth noting that the canopies of daffodil ‘Thalia’ in tall fescue, as well as crocus ‘Remembrance’ had excellent foliage development in 2020 in both turfgrasses. It remains to be determined if these bulbs’ performance in this location might improve in following years. With respect to mowing regimes, it bears notice that at the time mowing treatments were initiated the bulb canopies appeared full and photosynthetically active. Therefore, it is encouraging that even mowing three

times did not negatively affect bulb performance.

Previous research reported that neither herbicide application, nor timing to start mowing, impacted bulb persistence and performance under warm-season hybrid bermudagrass and buffalograss lawns. Although bulb emergence was not affected by turf species, visual impact of the bulbs was diminished in tall fescue, especially for those species which bloom height did not exceed 15 cm (e.g. crocus, grape hyacinth, Siberian squill, and glory-of-the-snow). Color also played a role in visual impact, with higher-contrasting white and yellow-blooming daffodil cultivars, achieving higher scores, compared to the blue- to violet-flowered crocuses and grape hyacinth.

The latter bloom was more noticeable earlier in the season (i.e. early March) when the cool-season tall fescue was of lower height. Daffodil cultivars may be more appropriate for interplanting with cool-season grasses. We used a specially designed bulb planter which undercut the turf; in the two years following planting, turf recovery appeared satisfactory, therefore we conclude that the bulb planter did not negatively impact turf health.

The polylectic pollinators and syrphid flies were observed nectaring on crocus, grape hyacinth, and Siberian squill as well as early-flying spring small bees warming on yellow blooms of daffodil ‘Tete-aTete.' Although ground-nesting bees in turf areas are generally regarded as not desirable, their visitation to flowers in intercropped lawns could have implications for biodiversity; therefore we consider that select spring bulbs could be a valuable addition to managed turf lawns to provide beneficial insect early-season nectar source and habitat.

This study demonstrated that warm-season and cool-season lawns could be successfully interplanted with early-spring geophytes under subtropical climate, however species and cultivars selection is essential to ensure long-term attainment and maximum aesthetic appearance.

Best flowering bulbs in 2020, crocus ‘Ruby Giant’ (A, tall fescue, B, hybrid bermudagrass) and daffodil ‘Tete-a-Tete’ (C, tall fescue, D, hybrid bermudagrass). Photos taken March 6, 2020.

Canopy of crocus ‘Remembrance’ in hybrid bermudagrass(A); height of bulb blooms in relation to height of tall fescue, crocus ‘Remembrance’ (B), grape hyacinth (C), and crocus ‘Ruby Giant’ (D). Photos taken in March, 2020 (A) and March, 2019 (B-D).