Flower Bulb and Lily Postharvest Research at Cornell

My colleague Chris Wien, who normally graces this spot in the Quarterly, has taken his part-time retirement to heart and asked me to write the column this time. I thought I’d take the opportunity to tell you a bit about my overall research program at Cornell and some thoughts on lilies and lily postharvest handling.

Background, Flower Bulb Research Program

First, the program. In the mid-1960s the Dutch export industry initiated a research program at Michigan State University to focus on developing information specific to the North American bulb forcing industry. The program began in 1965, and under the leadership of Gus de Hertogh, rapidly developed information on cold-week requirements and forcing suitability for many bulb crops, especially tulips. By the late 1960s and early 1970s, plant growth regulators (PGRs) were becoming more available to the industry, and Gus did a significant amount of work on PGRs to tailor tulips as potted plants. This work expanded to include hyacinth and daffodil, then onto lilies and a number of other bulbous crops. Ultimately, the Holland Bulb Forcer’s Guide (in its many editions) became the centerpiece of the program through the mid-1990s, with Gus’ retirement.

Without prolonging the story, I moved to Cornell and assumed leadership of the Flower Bulb Research Program in 1998. By 2000, Cornell had invested a substantial amount into the program, building three state-of-the art coolers, remodeling a laboratory and rebuilding two greenhouses (some 6,000 sq. ft.) to support the program, and another 6,000 sq. ft. of glasshouse has been rebuilt in the last 3 years.

Our main research program support, however, continues to come from the Dutch export industry through Anthos, the trade association that represents bulb, perennial and nursery stock exporters worldwide. Our main goal is relatively simple. The information we generate helps North American flower bulb forcers grow a better product that in turn helps increase exports from Holland. So, in principle, we have a better product for the customer, better sales and profits for North American growers, and increased exports and a larger market for the Dutch export industry. 

Most of our findings find their way  onto our website, http://www.flowerbulbs.cornell.edu

We continue to evaluate tulip, hyacinth and narcissus cultivars for suitability as potted plants. Especially with tulip, this involves cooling bulbs for varying lengths of time. Basically, the longer the cold period, from ca. 12 to 20-22 weeks, the longer the stem. For pots, less cold is better (since you end up with shorter plants), but for cuts, a longer cold period, all things being equal, is more desirable. Also, the exact temperature of the cold is important. “Warmer cold” (for example, 48F) leads to shorter plants with larger flowers, for a given duration of cold. A “colder cold” (for example 34F), leads to taller plants and smaller flowers for the same cold duration. Thus, optimum handling of a given tulip cultivar is different if the bulb is destined for cut flower or pot plant forcing.

A comprehensive listing of tulip cultivars and their suitability for cut flower or pot plant use can be found on our web site. The data there are derived from our own Cornell research, and some is adapted from the Forcer’s Guide.

We also do studies on landscape perennialization of bulbs, combinations of bulbs and perennials (http://www.hort.cornell.edu/combos/) and other landscape-related topics.  In forcing, we have done extensive work on growth regulators on a wide range of new cultivars and on plant physiological and practical industry problems.

A Brief Worldview of Lilies

Worldwide, lily is one of the most widely grown cut flowers. Most of the bulbs forced in the world are grown in and imported from Holland. The nearby table shows the bulb production area (in hectares, multiply by 2.5 to get acres). This table does not include lily acreage in other production locations in Europe and especially the southern hemisphere crop (Chile, Australia, New Zealand, etc.) which is important for maintain year-round available of forcing bulbs. This shows a decrease in production acreage in the last 5-6 years and also relative changes in acreage. Most notably, the area of Asiatic hybrids is decreasing, with much of that being replaced by LA hybrids (hybrids derived from Asiatic cultivars crossed with longiflorum). Also, one can see a decrease in oriental hybrids. It is expected this decrease will be made up with increases in the OT hybrids (orientals crossed with trumpets).

Lily breeding is perhaps the most advanced and dynamic example or ornamental breeding in the world. Breakthrough work by Jaap van Tuyl’s lab in Holland led to the ability to cross widely separated species, and has ushered in groups such as LA-hybrids (longiflorum-asiatic), LO (longiflorum-oriental) and OT (oriental-trumpet).Within each of these group dozens if not hybrids of cultivars exist.

‘Sorbonne’ dominates the list of top lily varieties. It was not even released until 1994, whereas ‘Star Gazer’, by far the most important lily in 1994, has fallen out of favor and will face the prospect of literally becoming extinct in a few years.  In general, since lily breeding is so sophisticated and done on such a large scale in Holland (here, I am referring only to commercial cut flower breeding, not hobbyist and local garden breeding), hundreds of cultivars are released each year and breeders have an interest in getting growers to adopt them as quickly as possible. And exporters have an interest in getting their forcing customers to adopt them at a similar pace. Only through trialing at one’s own facility and at different times of the year can a grower be sure a new cultivar will perform better than a currently produced cultivar.

A Few Thoughts on Lily Postharvest Handling

The basics for lily postharvest handling are simple. There are two concerns. First, to reduce or eliminate the potential for leaf yellowing, it is important to treat stems with a product containing gibberellin4+7 (GA4+7). An example is Chrysal BVB, which is labeled for after-harvest treatment of lilies. This is a grower-level treatment, done shortly after stems are harvested, as a pulse, either in the cooler, or at room temperature (see BVB label for specifics). Other products, such as Fascination, contain GA4+7 and are also effective but are not labeled. The second main issue is to provide customers with a packet of lily food for the vase. There are many options here and Floralife and Chrysal both have offerings. The important point is a sugar source and a biocide (to reduce microbial growth).

Sugar is extremely important for maximizing lily flower life. We have looked at many lily cultivars (mainly LA and oriental hybrids) and invariably see longer flower lifespans when sugar is included in the vase, and many other published studies show the same result. Sugar also intensifies flower color, especially for flowers that open later. An undesired side effect of vase sugar is occasional leaf yellowing that some have reported.  We have not regularly seen this in our work, perhaps because leaf yellowing in lilies is dependent on many factors, including the cultivar, storage after harvest, storage temperature, and possibly other factors (greenhouse environment, season, etc.).

Regardless of whether vase sugar (especially, in the concentrations resulting from correct use of lily food) causes leaf yellowing or not, pretreating with GA4+7 (Chrysal BVB) will eliminate yellowing problems. A side benefit is that flowers will tend to last even longer due to the GA treatment (this was shown in our original research on gibberellins and potted lily plants, and by other research dating to the mid-1960s).When used as an integrated system, the GA4+7 can literally stop leaf yellowing (which is exacerbated by cold storage, and is cultivar-dependent).

Two other points deserve mention. Are lilies ethylene sensitive? Yes and no.  Most lilies are sensitive to ethylene in the greenhouse, with small buds being especially sensitive. Malfunctioning heaters that release ethylene can lead to ethylene accumulation during winter greenhouse production and will severely damage lilies. For most cultivars, however, open flowers are not especially sensitive to ethylene. If harvested stems are cold stored for a significant period (perhaps 7-10 days), young buds will abort when moved to warmer temperatures. This is probably related to increased ethylene sensitivity due to carbohydrate shortage from the long storage. In summary, under “normal” situations where lengthy cold storage is not needed, most lilies can be considered relatively non-sensitive to ethylene.

The second point is temperature. What is the best storage temperature for lilies?  Some published recommendations call for shipping and storage temperatures to be 1-2C (34-36F). While a good general recommendation, low storage temperatures can lead to several physiological problems. Storage-induced leaf yellowing is generally made worse by lower storage temperatures. Pre-treating with GA4+7 as described above is important, but if this treatment is not available, I would recommend storing lilies at slightly warmer temperatures (40-42F) and not at 34-36F. Secondly, moving certain lily cultivars from a full sun, warm greenhouse into a 35F cooler can cause an ugly “blotch” of brownish, sunken tissue on the buds. This problem occurs within 2-3 days of placing stems in the cooler and can happen on puffy, nearly open buds as well as smaller unopened ones. The solution is to first store stems for a day at temperatures in the 7-9C range (45-48F) before moving to a lower temperature. More information on this problem can be found on our website in the “Research Newsletters” section.

I welcome your questions and comments.

Table 1. Acreage (in hectares) of the Dutch lily bulb crop (in Holland) since 2006.

 

 200620082010
 Aurelian71417
 Asiatic hybrids641553409
 L-A hybrids782983835
 L-O hybrids373046
 Longiflorum1234827
 O-A hybrid010
 O-T hybrids215251307
 Oriental hybrids175514461504
 Misc.443134
 Total360433573180

Bill Miller

Bill Miller is Professor of Horticulture at Cornell University. Contact him at [email protected]