This spring I was rushing to attend the local flower show in Cincinnati, Ohio. I was hosted by the American Daffodil Society and needed some gifts. But what?
Flowers? Sweets? Books? Perhaps a good bottle of wine? I am a guy who plans everything, but identifying and locating a suitable gift is not easy. I am already on the road and time is running out. I pull in to the Meijer grocery store hoping to find something proper.
To my surprise, this particular store has an outdoor garden section with an even more surprising selection of annuals, perennials and bulbs. I find some very nice 6-inch pots of daffodils, as well as 3-gallon containers of patio lilies.
Calla lilies in 8-inch pots also catch my eye. I’m impressed to find all these callas and that there are many colors available. I’m so impressed with the quality and show of the calla that I buy several pots and make an excellent impression with a smashing gift for my hosts.
Seeing these new cultivars piqued my interest. I wanted to learn more about what is currently being introduced into the market. The older cultivars can be tricky to grow and I wanted to learn what the new breeding and new colors are all about.
In my research, I learned callas fit many market segments. Most growers know callas can be grown as a pot plant or cut flower. Few, however, know some cultivars fit nicely into any program for bedding plants, upscale patio containers or specialty cut flowers. Callas are unusual items that can make up a perennial program in USDA climate zone 7 or higher, and they’re an exotic-looking plant that fits the water gardening market.
I was impressed with what I saw and learned, in particular how the new cultivars performed in the greenhouse and with the consumer. I was even asked to select the newest and hottest calla hybrids to be presented on “The Martha Stewart Show” back in April, when Martha Stewart presented them on her show.
Now realizing the various uses of callas and the cultivar improvements by breeding programs, I wonder: Is the industry ready to take on callas in a big way?
What Are Callas?
The calla lily’s botanical name is zantedeschia, many of which are native to South Africa. Zantedeschia consists of 28 different species, several of which have found their way into modern hybridizing efforts.
The different calla species have adapted to a wide range of environmental conditions. Most are heat loving, whereas a few can withstand some cold, even slight frost. The aquatic forms flourish in water with the root system completely submersed, while others handle dry spells without a problem.
Generally, callas can be described as a tropical perennial plant that remains evergreen, as long as water and temperature remain in an acceptable range. During dry spells or cold periods, plants go dormant and foliage is shed. The natural range of zantedeschia includes areas with defined rainy seasons occurring either in the summer or in the winter.
The different species have adapted to this environment and bloom in the dry season. As diversely adopted to climatic conditions is the growing habit. While some species grow fairly compact, others may grow up to 6 feet tall. Callas have a reputation for doing well even on poor soils.
Planning Your Calla Program
The first step to create your own calla lily program is to find a reputable supplier. There are a number of companies and sales people selling callas. Some are significantly better than others. But remember: Good quality bulbs and tubers cost money, and so does good service. With bulbs, and especially with callas, you get what you pay for.
Superior customer care (yes, a grower is a customer too) is particularly important when starting a new product line. It is not easy to switch to new crops–things may go wrong when the program is not well planned out. Although new calla hybrids are a lot easier to work with, they still require advanced growing skills and good planning. A good sales rep that has interest in your business can give you tips and support that will make your new calla program succeed.
When choosing cultivars, look not only at the flower color but understand that some cultivars may grow more vigorously. They may need special attention, such as a plant growth regulator (PGR) program. The growing habit of the different cultivars includes vigor and how quickly a given cultivar will flower, as well as disease resistance–the range of these habits is remarkable and the result of successful plant breeding.
Your supplier needs to let you know about habit and tuber sizes for the different cultivars. Perhaps the most frustrating aspect starting a new program is tuber availability, especially of the latest cultivars. Include your supplier in the planning process–there is nothing more aggravating like planning a program and finally learning that this particular cultivar or tuber size is unavailable.
The tuber size available will more or less determine which container you work with. The different suppliers ought to provide you with detailed information regarding the different cultivars, pot sizes and bench space requirements. Tubers of most calla lilies can be ordered as two very different items:
1. The prepared or “ready-to-go” tubers. These are ready for planting. The tubers should have been treated with gibberellic acid (GA) as well as programmed. These tubers should arrive at your greenhouse with small shoots showing. They need to be potted right away. Short-time storage for a few days at 65°F may be possible, but these tubers want to grow–potted or not!
2. The unprepared or “more-work-is-needed” tubers. These tubers arrive at your greenhouse unprepared and are not ready for planting. They can be stored for up to eight months if you have sufficient cooler space and excellent cooler environment controls. Most facilities only support a month or two for storage before damage to the tubers can be expected. The tubers must be stored at a temperature set point of 48°F and relative humidity must be maintained at a range of 70 to 80 percent. Provide a low but constant airflow to prevent blue mold on the tubers.
Treating & Buying
To start preparation, move tubers into an area that has a temperature set point of 65°F and supports high relative humidity at a range of 80 to 90 percent. The next step is to treat your tubers with GA. Suggested chemicals and rates ought to be provided by your supplier and your extension agent.
Do not pot at this point. You need to wait until the tubers develop small shoots. It takes a minimum of three weeks from the onset of preparation to initiate shoot development. Once shoots develop, you have prepared tubers and they are ready for potting. As you can see, working with unprepared tubers creates yet another layer of logistics and planning.
Buying in bulk and storing tubers can save you money with fewer expenses for shipping and get you a potential discount for ordering a large amount of tubers. In addition, you may have more control over the assortment.
From Potting To Bench
Close attention should be given to potting media, water needs and the greenhouse environment for growing a high-quality calla crop. There are also some very basic guidelines to follow when working with tubers.
Check your tubers regularly, when receiving a new shipment and again when you are potting. Check for damage and disease. Lesions and soft spots on tubers are a sure sign of trouble. Especially watery and rotten areas are symptoms of erwinia.
In addition, infected tubers often smell bad. Do not plant these tubers. They need to be removed and destroyed. To prevent further spread of the erwinia bacteria, disinfect all surfaces and areas these tubers came in contact with. Healthy-looking tubers of a batch that contained contaminated tubers need to be treated with an approved dip or drench. My advice: get rid of the batch and get a replacement from your supplier.
Several good potting media are available. As a general rule, your media of choice should have the following characteristics:
1. Be soilless and well draining. A potting mix that may contain coir, rice hulls, pine-bark compost, No. 2 or No. 3 sand and other coarse materials is ideal. Avoid media that contain a lot of fine particles which may lead to waterlog in the pot.
The proportion of the coarse amendments should be 70 to 90 percent of the total volume. However, if you choose to work with bark compost, keep in mind that pine-bark composts will bind some PGR, particularly Bonzi. I have had good experiences adding biological root rot suppressants such as RootShield at a rate of 1.5 pounds per cubic yard. RootShield certainly will promote root health and prevent soil-borne fungal diseases.
2. A potting media pH between 5.8 and 6.2. Add lime if the pH is too low and make sure a sufficient starter charge of nutrient, including a micronutrient, is included in the mix. However, keep the EC moderate to low. Excessive salts may burn the newly developing root system, especially early in the production cycle when nutrients may leach out with irrigation water.
Determine the right dimension of the pots based on the size of your tubers and the habit of the cultivar. These need to be in the right proportion. Generally, standard pots or extra tall pots work best.
Also, watch your potting line during potting. It is sometimes hard to figure out the upside of a tuber, especially when the shoots are still very small. The tubers must be planted upside up with about ½ to 1 inch of potting media covering the crown. The pots need to be watered in well, right after potting.
To keep bench space open, at least for a while, the newly potted callas can be stored on carts. The storage area should be moderately warm (60 to 68°F), which may be in your head house or somewhere else out of the way. Callas don’t need to go onto the bench until the first leaves have developed, but you still need to check the pots from time to time.
Keep the pots evenly moist (there is a difference between moist and soaking wet!) but make sure they don’t dry out. Proper water management is the most important aspect in growing high-quality callas, especially when starting the crop. Absolutely avoid going from too wet to too dry. Extreme changes in water status promote rot of the root system and eventually of the tuber.
This stage starts when pots are moved into the greenhouse, which may occur right after potting or following the storage stage. Callas in this stage need a proper temperature and the right amount of water and fertilizer. Sufficient light and pot spacing are also important to the crop’s success.
Temperature & Light
The temperature requirements of the greenhouse production cycle can be broken down into a sequence of three stages.
1. Planting to shoots visible (shoots less than 2 inches tall). It takes 14 to 21 days to complete this stage. During this time, maintain a constant temperature range of 62 to 68°F. Do not use DIF or DIP during the rooting and early growing stage.
2. Shoots 2 inches to first flower. Provide a temperature range of 60 to 75°F during the day. Drop temperatures during the night between 55 and 60°F. A negative DIF and/or DIP are very effective treatments for controlling plant height. DIP is the pre-dawn cooling of the greenhouse.
3. First flower to harvest. The suggested temperature range is the same as the second stage. However, lowering the temperature in this stage may improve flower pigmentation and longevity of the blooms.
Calla lilies require the right ratio of light and temperature. This ratio determines whether a crop will be just good or a knockout. Pushing a crop during a low light period or as a result of excessive shading may result in weak plants with low flower count. High light is needed for superior pigmentation of the blooms and a strong structure of the plant, especially when pushing callas at their upper temperature limits.
Still, the margin of high light and too much direct sun is slim. Make sure to provide sun protection using a 50 percent shade cloth, especially in the spring to prevent sun burn. Callas are daylength neutral. Therefore, there is no photoperiodic effect of plant development with intermittent lighting. The total amount of light, which is the sum of natural light and artificial light, affects plant habit and flower pigmentation. During low light periods, crop quality can be improved by lowering temperature. Invest in a couple more weeks of bench time and be rewarded by a “wow” crop.
Some of the unfavorable responses to suboptimal conditions can be counteracted with the application of PGRs.
The Greenhouse Environment
Calla lilies require moderate to high relative humidity (RH) for good development and growth. The suggested level of RH has a range from 65 to 75 percent. Levels below 50 percent or extreme changes of RH are frequently the cause of brown crisp edges on foliage and flowers. Condensation and free water on foliage, especially during the night may lead to fungal diseases like botrytis.
To manage and maintain a proper RH level, a combination of ventilation, shading and temperature adjustments should be used. Maintain some air flow to prevent fungal diseases.
Irrigation, IPM & Fertilization
Overhead irrigation with watering booms, ebb and flow systems and drip irrigation systems works well. Especially when working with overhead systems, make sure the nozzles of the boom are well calibrated and water is broadcasted evenly. Uneven watering and dry spots may cause problems because callas depend on a constant supply of water.
Stressed plants become quickly compromised by fungal infections. A few sick plants in your crop can lead to serious trouble by infecting more plants. Good housekeeping and cleanliness are always important in the greenhouse, but especially important when growing callas. You really must remove sick plants. Check for symptoms of disease on foliage, and check the root system as well.
Symptoms to watch for include soft rot of stems, odor from the pot, white fungal growth on plant tissue and discolored and oozing root systems. If you notice any of these symptoms remove plants. Most of these problems can be prevented with proper water management. But in some cases a fungicide program may become necessary.
Try to maintain even moisture throughout the crop cycle. Callas require an increasing amount of water as they grow in size. Newly potted plants need to be kept slightly on the dry side. As the first leaves unfold, the amount and frequency of watering increases. Limit overhead watering to the morning, as moisture on foliage going into the night may promote fungal disease.
Callas respond well to constant feed with a 100 to 150 ppm solution. Several complete liquid fertilizers can be used as long as nitrogen (N) is moderate, phosphorus (P) low, and potash (K) moderate. A good ratio is 4:1:3 such as a 16-4-12 fertilizer. A suitable fertilizer should supply a complete range of micronutrients as well. Test your soil and keep an eye especially on magnesium, which should be present at an amount of 1 to 1.5 mmol.
When choosing a fertilizer, make sure it does not add calcium sulfate or ammonium bicarbonate radicals. Callas seem to be intolerant to these radicals. Try to maintain a range of 1.2 to 1.7 m/S and always maintain an EC below 2.0 m/S.