Developing "Bud Sticks" for Hybrid Lilies

In response to requests from U.S. lily growers, we have been working to develop “bud sticks” or “timing tools” to predict flowering dates based on bud size for a range of hybrid lily cultivars. This article will present a brief background on what we have done, illustrate the results, and provide a link for further information for timing 30 cultivars of Asiatic, oriental, LA, and OT-hybrid lilies.


Accurate prediction of the date a lily bud will flower is important for proper timing for holiday or special occasion sales. When stems are marketed daily (as with the Dutch auction) it might not be important if a crop flowers today or 4 days from now. But for holiday markets, special events like weddings, or for specific promotions, accurate prediction of the flower date many weeks in advance is important so you can deliver a stem at the right specification (1 open bud, 2 colored buds, etc.) at the right time. 

When grown at a given temperature, time to flower from a specified development stage is remarkably constant. In the case of lilies, bud length is easily measured and is an excellent way to monitor development. If you grow a lily cultivar in a constant environment, a 3.7 cm long bud (for example) will always flower in a specified number of days in the future. If the plant is grown warmer, the plant will flower faster, and if grown cooler, it will be slower. Thus, temperature is the key environmental factor that regulates flowering of lilies. Light does play a role, especially if higher light levels warms the plant above the air temperature, but temperature is the most important factor.

Because plants must flower for Easter, the potted Easter lily is one of the most highly studied floriculture plants in terms of growth rate and temperature. Timing of ‘Nellie White’ (the main cultivar used for Easter pots) is controlled by adjusting temperature so that “visible bud” falls 5-6 weeks before sales date (it is well known from research and practical experience that an Easter lily at “visible bud” will flower in 6 weeks if grown at 15.6C (60F) night temperature). 

After visible bud, in the 5-6 weeks before flowering, a long-standing tool called a “bud stick” is used. Essentially, the bud stick is held up to the bud, and marks indicate that a given length bud will take a specific number of days to open as a particular temperature.
However, given the many groups and cultivars of lilies, it is clear that “bud sticks” need to be developed for individual varieties. The purpose of this ongoing work is to develop timing tools for a number of cultivars of hybrid lilies, including many grown as cut flowers.

What We Did

A range of lily cultivars was grown over the past five years at Cornell. We planted 8-9 bulbs into lily export crates in Lambert LM-111 mix and grew the plants with normal care. For each cultivar, when the bottom (oldest) buds became long enough to measure without greatly disturbing the young leaves surrounding them, crates were moved to 4 or 5 greenhouses at temperatures. Buds were tagged and bud length measured 2-3 times per week until they flowered. Knowing the flower date, it was possible to calculate the number of days to open for all the bud length measurements collected. 

Ultimately, a large data-base of days to flower and bud length was developed for each cultivar and temperature. These numbers were plotted onto a graph, and equations relating bud length and days to flower across the temperatures were calculated. I’ll spare additional details on the “sausage making” aspect of the work! Ultimately, a simple table showing days to open at different temperatures for various bud lengths was developed. Note this table is presenting temperature at the 24-hour, average daily temperature (ADT).

What We Found

The table shows results for an LA (‘Samur’), an oriental (‘Sorbonne’) and an OT (‘Tabledance’). First, you can see that growing the plants at a warmer temperature greatly reduces the days to flower (for example, if you grow ‘Sorbonne’ at 72F versus 61F, you will reduce the time to open a 0.8-inch long bud by 17 days (45 days at the cool temperature versus 28 days at the warmer temperature). You can see differences between cultivars. For example, a 0.8-inch long ‘Samur’ bud takes 33 days to flower at 61F, but the ‘Sorbonne’ bud takes 45 days. And, obviously, smaller buds take longer to open than larger buds (example: ‘Tabledance’, 1.6-inch buds open in 37 days at 61F, but 4-inch buds take only 8 days).

An extensive presentation of data for 30 hybrid lily cultivars (both cut and pot varieties) can be found at


Growers can make use of this information in a number of ways. First, a deeper understanding of the relation of temperature and growth rate can be useful in its own right. To make full use of this information, growers would need greenhouses with good temperature monitoring equipment which would allow easy calculation of daily averages (preferably accumulated averages).

Bill Miller

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

Neil Mattson

Neil Mattson is Associate Professor of Horticulture at Cornell University. Contact him at [email protected]