Easter lily is an ornamental crop grown in greenhouses in the USA in the weeks before Easter each year. It is extremely important to control crop development very precisely so that the crop is ready for sale at just the right date. Greenhouse temperature control is the variable which growers can control to achieve the desired target flowering date.
Many growers now use a lily 'bud meter' that was developed in 1984 by Will Healy and Harold Wilkins at the University of Minnesota. This device is used to track the elongation of flower buds on Easter lily plants. The bud meter shows how many days until a bud will flower, for many combinations of temperature and flower bud length. Since the original bud meter was inaccurate for small buds, we recalibrated it with new data collected through greenhouse experiments at several locations and temperature conditions. On this page you see the most recent version.
This tool is useful for two purposes: (1) to determine when plants will be ready to ship or to be placed into a cooler for storage, or (2) to determine an optimum average greenhouse temperature level so that the crop will flower on a selected date. Thus if the tool indicates that the crop is going to flower too early or late, then a better average temperature can be selected.
Figure: Bud meter calibrated for Nellie White Easter lily. (not to scale unless the width measures exactly 20 cm).
To make your own bud meter, either download one of the files or print out the bud meter on this page. Then use a standard ruler with centimeter markings to verify that the centimeter graduation on the bottom of the ruler is correct. If not, you need to enlarge or reduce the figure (with a photocopier) until it is exactly the right size. You can compute the exact percentage of enlargement or reduction needed by dividing 2000 by the exact length (in centimeters) of the bud meter that you printed out.
Paste the bud meter onto thin cardboard. Laminating it will help it last in the greenhouse and is definitely needed if you printed it out with water-soluble ink (i.e. using an inkjet or dot-matrix printer). Otherwise, you'll get black spots on your hands and on the white flower buds (not a pretty sight).
This particular bud meter is calibrated solely for use with 'Nellie White' Easter lilies. It is used as shown in this photo:
Photo: Bud meter being used.
To use the bud meter:
Be aware that the Days to Flower on the meter refers to the first day when the flower bud petals split open. Lilies should be shipped or cooled at least one day before open flower - often at what is called the 'puffy white bud' stage. Take this difference of one or two days into account when calculating your target days to flower.
Note that bud meters are simple tools intended to help, not replace, your experience in local growing conditions. In the validation trials, the new bud meter predicted flowering date to within three days of observed flowering date when used as early as thirty days before flower. When the bud meter was used closer to Easter (less than ten days to flower), the tool was accurate to within two days.
Fisher P.R., Lieth J. H. and R.D. Heins, 1996. Modeling Flower Bud Elongation in Easter lily (Lilium longiflorum Thunb.) in Response to Temperature. HortScience, in press
Healy, W.E. and H.F. Wilkins. 1984. Temperature effects on 'Nellie White' flower bud development. HortScience 19(6):843-844.
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[updated: Aug 98]