Fact Sheets
Specific Crops
High oil, tough choices - Scheduling the 2009 Easter Lily Crop
With record high energy prices lily growers will be looking for ways to reduce oil consumption or cut production costs. Tighter crop spacing, increased double cropping and lower forcing temperatures are the steps most growers resort to first. However, last year some growers added an extra layer of plastic film, suspended above the truss, to provide some extra insulation. Energy conservation and the use of moveable energy curtains are good ideas should be top priorities but the use of an extra static barrier has some negative consequences that you should consider.
Figure 1. In 2008, some growers added an extra layer of plastic film to reduce oil consumption. This added layer of insulation reduced heat loss but also reduced light that directly affects plant development. Any reduction in light, from overhead structures or baskets, will affect lily development.
Easter lilies are a high light crop. Every time you add an extra layer of plastic film, you reduce light transmission by as much as 10%. If the film collects condensation and dust, light transmission is further reduced, and of course more overhead baskets reduce light even more. The best quality lilies grow under maximum light conditions. As light is reduced, stem stretch and the incidence of lower leaf yellowing increases. If increased overhead shading is combined with tighter spacing, the incidence of stem stretch and leaf yellowing will increase even more.
As always, how we manage temperature is dictated by the lily schedule and the amount of leaf and bud development we need to achieve over a fixed period of time. Some lily forcers grow at cool temperatures for most of the crop and then push hard at the end. The rationale is that it costs less to run high temperatures in April then in February. If you choose to do this you still need to keep in mind just how much lily development you can reasonably expect to force in the final weeks. For example, a 15°F increase in average daily temperature (ADT) from 59°F to 74°F will increase leaf unfolding rate by about 0.8 leaves per day (from 1.3 to 2.1 leaves per day on average). Over a 1-week period this will only advance development an additional 5.6 leaves. You would achieve the same thing by increasing ADT from 59°F to 63°F over a 4-week period. Bud development shows a similar response. Finally, the increase in leaf and bud development you can expect to achieve begins to level off at very high forcing temperatures and stress on the plant increases significantly.
In 2009 Easter falls on April 12, this is mid-date Easter that will allow plenty of time for forcing (see the 2009 Easter lily schedule for details). This is good news since you can grow cool for most of the schedule and still bring the crop in on time.
The normal Easter lily schedule for pot-cooled bulbs takes a total of 23 weeks. This includes 3-weeks in the pot at 60-62°F to stimulate root development, 6-weeks of bulb cooling at 40-45°F and then 14-weeks of greenhouse forcing at 60-65°F or higher as needed. For case-cooled bulbs the process is still 23 weeks but this includes 6-weeks bulb cooling at 40-45°F and then 17-weeks of greenhouse forcing.
This season start bulb programming by November 2 (23 weeks before Easter). However, bulb programming must begin as soon as bulbs arrive and they may arrive early (24-25 weeks before Easter). If you have extra time you will have the luxury of growing cool or you can use the extra time in other ways. One option is to begin cooling the bulbs at recommended temperatures (40-45°F). After four weeks, drop the temperature to 32-34°F but make sure bulbs do not freeze. This will slow vernalization, so that the bulbs can remain in the cooler longer without "perceiving" more than 1000 hours of vernalization.
A second option is to run cooler than normal temperatures after primary buds initiation begins to stimulate secondary bud formation and slow lily development. Just vernalize bulbs as normal, then move into the 60-62°F greenhouse 18 to 19 weeks before Easter. Once the primary buds begin to initiate, lower greenhouse temperature to 46°F. Maintain temperatures for 7-10 days to stimulate secondary bud formation. After this period, raise the temperature to 60-62°F until bud initiation is complete.
Timing of the cool temperature treatment must start with primary bud initiation, which coincides with stem root initiation or when shoots reach about 3” high. Check bud initiation by dissecting some lilies and use a magnifying lens to view the anatomical changes in the shoot tip or look stem roots that begin to form (1/8”) at about the time bud initiation is starting. If the temperature is lowered before bud initiation starts, flower bud initiation may be adversely affected or delayed. If the temperature is lowered after bud initiation is complete, it will have no effect on bud count but it will slow lily growth.
Greenhouse forcing: After cooling is complete, immediately move the potted bulbs into the 60-62°F greenhouse, by at least week 17 for case-cooled bulbs or week 14 for pot-cooled bulbs. During the first few weeks of greenhouse forcing do not allow bulb temperature to reach or exceed 65°F as some of the cooling effect will be lost. If you were unable to achieve the full cooling before greenhouse forcing starts, you can use insurance lighting as soon as lilies emerge BUT insurance lighting should not be required on the 2009 crop. Lilies begin emerging from 1 to 3 weeks after forcing begins – record the emergence date and separate lilies into early, mid and late emergence groups, and record the ADT following shoot emergence. Bud initiation starts soon after emergence and is complete when shoots reach about 3” tall. Run 60-62°F until primary buds initiate is complete.
Leaf counting & crop timing: Use temperature to control the rate of lily development for the rest of the forcing period. The rates of both leaf and flower development can be controlled with temperature so use temperature to control when the crop reaches the saleable stage. For example, at 72°F leaves unfold at a rate of 2 per day on average, while at 63°F the rate decreases to 1.5 leaves per day. Likewise, a lily will go from visible bud to bloom in 24 days at 81°F, 31 days at 70°F, 35 days at 64°F and 42 days at 59°F. If you arrive at visible bud 5 to 7 weeks before Easter and you can control temperature within these limits you should be in good shape to finish on time. Finally, plants that bloom early can be held in a cooler for up to two weeks. Storing finished lilies for longer than two weeks in not recommended.
Start leaf counting after bud set is complete. The leaf counting technique is based on the fact that once flower buds initiate, leaf number is set and will not change, however the exact number of leaves varies from year to year, with bulbs from different sources or bulbs exposed to different cooling conditions.
After bud initiation, select several plants in each lily group -- bulb source, emergence time etc. – that are representative of the overall group, and remove, count and record the total number of leaves on each. Use magnification and a needle to remove and count the smallest, un-expanded leaves. (Note: The shoot tip should show evidence of tiny flower bud formation. If this is not the case, you started counting too early. Wait one week and try again.) Record the number of fully developed leaves (those at a 45° angle to the stem or greater) and the number of undeveloped leaves (those at an angle less than 45° to the stem). Divide the number of fully developed leaves by the days since shoot emergence. This is the “current rate of leaf development”. Divide the number of undeveloped leaves by the number of days remaining until visible bud. This is the “required rate of leaf development” or the rate you need to maintain as you more forward in the schedule. If the “current rate of development” is too fast, reduce the temperature in the greenhouse. If the “current rate of development” is too slow, increase the average greenhouse temperature.
Determine a new current rate each week (the rate since last count) and a new required rate. Determine the new required rate by subtraction - you do not have to destroy any more plants. Simply subtract the number of fully developed leaves from the average total number of leaves previously determined. HINT: You can flag your indicator plants and use a marking pen to mark the last leaf you counted as mature (Figure 2).
Figure 2. Indicator plants are flagged and the leaves marked with a marking pen. Each week the new leaves that unfold are counted to track the progress of lily development
Height control: The lily schedule has targeted heights at each week and is designed to produce a lily 16-18” tall at finish. Adjust these targets to fit your needs. Remember, lilies typically double in size during the bud development stage. Use plant growth regulators, DIF or a combination of the two to control plant height.
As previously mentioned, stem stretch tends to increase with low light as well as with warm temperatures and long days. Over crowding lilies or shading with overhead baskets will increase the tendency for lilies to stretch, and also reduce light penetration and increase the tendency for lower leaf yellowing (Figs. 1 & 3).
To control lily height begin applying PGRs (A-Rest, Chlormequat E-Pro, Concise, Cycocel, Topflor or Sumagic) as needed when shoots are 3-5" tall. Split applications provide the best results. You can apply any of the PGRs at ¼ to ½ normal rate, as needed, to control height. Reduce the concentrations of Sumagic used when combined with DIF. Use DIF, or cool morning DIP, to control lily height. Equal day/night temperatures, high night/low day temperatures or cool morning temperatures will keep lilies short.
Figure 3. Growing lilies with the carrying trays in place not only facilitates handling, it also sets the spacing and prevents the urge to space lilies too tight. Tight spacing and low light increase stem stretch and lower leaf yellowing.
Nutrition and Pest Management
Proper nutrition is essential for quality crop production. Inadequate nitrogen early in development leads to small bottom leaves that limit subsequent growth potential. Stimulate early leaf development by applying 400-600 ppm nitrogen at the first irrigation after emergence. The more leaf area the more sunlight the plants gather and that translates into greater growth. Phosphorus is also important in early lily development. Phosphorus is often withheld in lily nutrition to avoid leaf scorch caused by fluoride toxicity -- fluoride is a mineral element found in phosphorus-based fertilizers and some soil amendments. But phosphorus is also important for strong root development. Use a complete fertilizer formulation, such as a 20-10-20, for the initial feed. After the initial feeding use a 15-0-15 formulation, but if phosphorus was not added to the growing medium, alternate the 20-10-20 with the 15-0-15 formulation during greenhouse forcing. Fertilizer rates should range from 200-400 ppm depending on the frequency of fertigation.
Do not allow growing medium electrical conductivity to exceed 3-3.5 mmho/centimeter based on a saturated media extract. Periodic nutrient testing is advised. Testing the nutrient status of young but fully expanded leaves will provide the most accurate picture of lily nutritional health. Leaf tissue nutrient content should fall in the following ranges, 2.4-4 percent nitrogen, 0.1-0.7 percent phosphorus, 2-5 percent potassium, 0.2-4 percent calcium, 0.3-2 percent magnesium, 100-250 ppm iron, 50-250 ppm manganese, 30-70 ppm zinc, 5-25 ppm copper, 20-50 ppm boron.
Figure 4. Crop response to plant growth regulators vary with species. Here a drench of paclobutrazol (the active ingredient in Bonzi, Paczol, Piccolo and Downsize) effectively controls tulip height while these same chemicals are ineffective on Easter lilies. Note: Plants to the left received the drench treatment while plants to the right did not. For Easter lily, PGRs like A-Rest, Sumagic or Concise, and Topflor are effective materials to use.
Shed aphid 'skins' are a sure sign that a pest problem is starting. Systemic pesticides like Marathon should be applied a couple of weeks before visible bud (early to mid February 2009) as these materials move into leaves more readily than into flower buds. (Bottom) Sticky cards are useful to monitor populations of flying insect pests.
Aphids, fungus gnats and bulb mites are a major concern. Use only smokes or aerosols once lilies reach the bud stage. Many chemicals are listed for aphid control, including, Safari, Celero, Flagship, Tristar, Marathon, DuraGuard, Distance, Enstar II, Preclude TR, Tame, Thiodan smoke, Ultrafine Oil, Insecticidal Soap, Talstar and Endeavor. Fungus gnats can be controlled with many of these same chemicals as well as Citation, Adept, insect parasitic nematodes (Nemasys, NemaShield, Scanmask) and Gnatrol. Bulb mites, Rhizoglyphus robini, represent one of the more troublesome insect pests on lilies. Duraguard is labeled as a drench for soil borne organisms that may include bulb mites. Bulb mites are more likely to attack damaged bulbs – so be sure to rogue out bad bulbs and handle bulbs gently during potting, and control fungus gnats during forcing.
Easter lily production is always a challenge. Last year grower were up against the earliest Easter in a century (and many are just now recovering from the anxiety), this year the schedule is much friendlier but energy costs will be ferocious. As I indicated in this article there are ways to save on costs but you need to be careful that you limit the negative effects on crop quality. Have a happy and prosperous Easter in 2009.
Richard McAvoy
Professor and Extension Specialist, Greenhouse Crops
Department of Plant Science
University of Connecticut
Richard.mcavoy@uconn.edu
