Time to plan

Easter falls on April 16 in 2017, a late Easter date. Just as in the late seasons of 2014 (April 20), the 2017 schedule provides plenty of time for proper bulb programming as well as some extra time that growers will need to factor into their spring production plans.

Last year Easter fell on a very early date (March 27) and growers had to push hard all the way to the end to time the crop out properly. Pushing a crop hard to make an early Easter or pulling back hard to slow growth for a late Easter is not ideal and can diminish quality. Any added stress conditions tend to weaken plants, which creates an opening for root disease and insect problems to gain momentum. This year, the danger is that lilies will come in too early unless the extra time is managed properly. In part one of this two-part production series, we provide some scheduling tips and options for the first part of the production cycle. Look for part two in the October issue.

The ideal forcing schedule begins 23 weeks before Easter (Nov. 6 for Easter 2017) and includes six weeks for bulb cooling and 17 weeks for lily development in the pot. This season, bulbs shipped in mid-October may arrive 25 weeks before Easter (Oct. 23), adding as much as two extra weeks to the schedule. There are several options for using this time. You can bring the crop in early and hold the lilies in cold storage for up to two weeks. This may be a good option for at least a portion of the crop, as it will free up greenhouse space during a critical spring production period and most growers ship a portion of the lily crop starting around week two (Apr. 2 in 2017). This option requires adequate cooler capacity and a heavy reliance on the PGR Fascination to prevent leaf yellowing. Also, cold storage for more than two weeks will reduce flower life and decrease plant quality. Since lily quality will diminish with prolonged storage times, you’ll need to consider other options for the majority of the crop.

One option is to “lose” the extra time by dropping the temperature to 32-34°F mid-way through the bulb-cooling period. This will delay vernalization and allow you to start greenhouse forcing later without adding more than 1,000 hours to the bulb chilling process. Alternatively, you can make use of the extra time during bud initiation during the greenhouse forcing stage to increase secondary bud count.

Timing the crop

The 2017 schedule is timed for saleable lilies one week before Easter. Adjust the schedule back for earlier shipping dates. If your bulbs arrive a week or two before the targeted Nov. 6 start date, you will have some extra time on the schedule. The extra time is manageable, but plan ahead because it will be difficult to slow the crop down once the weather turns hot in late March and early April.

Start lily programming immediately as soon as the bulbs arrive. Begin by inspecting and cleaning bulbs, removing any debris and damaged scales, especially scales that appear punky or show evidence of infection. For case-cooled bulbs, make sure that the packing medium in the case is moist, and move the bulbs into the cooler at 40-45°F to begin the 6-week cooling or vernalization period. For pot-cooled bulbs, controlled temperature forcing (CTF) or natural cooling, plant bulbs in a well-drained medium and hold at 60-62°F in the greenhouse for 3 weeks to stimulate root development before beginning the 6-week vernalization period. Give the full 3 weeks for proper root development since there is no need to skimp on time this year.

Vernalization allows bulbs to produce a quality flowering shoot in a relatively short time. Six weeks of cooling is the standard rule, even though as little as 4 weeks of cooling will produce acceptable flowering. With longer cooling periods (beyond 6 weeks), lily shoots emerge earlier and more uniformly, but leaf number, bud count and the time from emergence to flowering are all reduced, and average internode length increases. You can prolong the cooling period without adversely affecting later crop development by dropping the temperature to 32-34°F as follows:

Start cooling at 40-45°F as normal, but after 4 weeks, drop the temperature to freezing or slightly above. The near-freezing temperatures will suspend normal metabolism, putting the bulbs in a near dormant state, during which additional vernalization will not occur. Bulbs can be held at this temperature until the extra time has elapsed, and then returned to 40-45°F for the remainder of the 6-week vernalization period. Beware though, that temperature must be carefully monitored and controlled with this technique. A light freeze of 32°F will not harm the bulbs, but colder temperatures may. If you only have 1-2 extra weeks in your schedule, I recommend you complete the normal 6-week cooling uninterrupted and make good use of the extra time to increase bud count later in the crop.

With naturally cooled lilies follow the CTF schedule, but know your limitations on controlling temperatures — especially during the vernalization period. You may not be able to hold the pots at 32-34°F to delay vernalization. However, if these temperatures occur naturally, you need to factor them into your schedule by subtracting any days that the bulbs experience 32°F from the 1,000-hour cumulative cooling period.

Once vernalization is complete, reassess your schedule. If you still have extra time, try to increase secondary bud set with cool temperatures and keep a close rein on crop development with cool forcing temperatures.

Watch for the second part of this two-part production series in the October issue, which will cover greenhouse forcing, leaf counting, height control pest, disease control and more.

Richard is a professor and extension specialist at the University of Connecticut.