Calla culture requires special attention to media selection, water management, temperatures and a preventative fungicide program. Each color and variety is unique in its growth habit and performance. Specific product information will accompany each order.

Please click here to read our "Must do" steps checklist, click on any of the topics below for additional information and explanation of each step, or scroll down to view the entire guidelines*.

Must Do Steps

1. Receiving and handling of dormant tubers

Unpack on arrival. Dispose of any soft rot and wash hands to avoid spreading the bacteria to healthy bulbs. Place in well ventilated trays at 65°F for one to two days prior to planting. For long-term storage, keep well ventilated at 50°F. Avoid excessive drying by keeping humidities at 80%.

2. Scheduling

Outdoors:

Callas are semi-hardy and cannot take a hard frost. If the ground freezes to the depth of the tuber, it will be destroyed. Light frost can be tolerated.

In Northern latitudes and California, open field-grown callas should bloom from early May to late July Excellent soil drainage is critical. Later plantings, when soil temperature approaches 60°F, usually result in less loss due to bulb rot, but also later flowers. Earlier field plantings or established blocks can be plastic mulched or tunneled for earlier blooms. Trial for your environment.

Greenhouse:

As a general rule, the earlier in the spring (or winter) that callas are planted, the sooner they will bloom. However, the number of days between planting date and bloom decreases with later plantings as warmer temperatures and longer days accelerate growth.

Callas can be grown in raised beds or in containers. Great soil drainage is critical. Planting rhizomes in portable Dutch bulb crates works well. 8 - 12 rhizomes can be planted per 15 x 24" crate, depending on tuber size. The plants can be grown in a heated greenhouse for early spring flowering and moved outdoors for vegetative growth, making greenhouse space available for another crop. Callas require 10 weeks of vegetative growth post flowering. Dormancy then requires another 8-10 weeks prior to regrowing

Progibb, the standard gibberellic acid (GA3) or Provide (GA4+7) or Promalin (GA4+7 with benzyladenine) treatments all increase the number of flowers and reduce the time between first and second flowers. Effect is greatest on gems and pinks, but GA is effective on yellows and whites to a lesser extent. A slight increase (5-10%) in flower deformation may occur on yellows and whites, but net gain in performance justifies its use.

GA will increase plant height, slightly reduce leaf width, and soften stems, especially in low light and shorter days. Promalin tends to cause less flower deformities than Progibb. Tubers can be dipped for one to five minutes in a 100-125 ppm GA solution or sprayed and allowed to air dry prior to planting. Addition of a fixed copper such as Champ II at 1 oz. per gallon to the solution can help reduce pathogen spread. Take care not to damage the sprout when dipping.

GA may also be applied with a backpak sprayer. Many growers prefer this method, as it reduces pathogen spread. Just lay the callas out and spray to drip. Try to get maximum coverage on all tubers. Allow tubers to dry slowly for at least 8 hours for maximum GA absorption.

Recommendation:

• 1.8% Promalin (GA4+7 +BA) solution: a 100 ppm mixture is 1.3 tbsp (20 ml) per gal. H2O (5.5 ml/L).
• 4% Progibb (GA3) solution: a 125 ppm mixture is 0.8 tbsp per gal. H2O (3.1 ml/L).

Callfornia callas preconditioned tubers for new plantings are highly recommended to improve disease management and ensure blooming.

GA on Permanent Plantings:

GA can be applied to established planting, without soil disturbance, prior to sprout emergence. A GA drench can be applied at the 100 ppm rate. The additional flowering effect will take 75-85 days. This method will increase flower yields and extend flower production, but, conversely, will decrease uniformity at harvest date as compared to the dipped, fresh planted bulbs.

Soil beds or pots can also be drenched with a 100 ppm GA solution if done during dormancy or within 5 days of initial watering of dormant bulbs. Soil should be moderately moist at time of drench to improve uniformity. Fungicides can be combined in the season's initial drench.

The bacterial soft-rot syndrome, which concludes with Erwinia carotovora, is generally preceded by water molds and Rhyzoctonia. Other wounds or stresses also add to this profit-impacting pathodgen complex. It is very important to follow media recommendations, use good sanitation practices and proper water, preventative drench and temperature management. In early forcing, most calla diseases are favored by overly wet and cold conditions. In summer growth, overly wet and excessively warm day and night conditions are also conducive to disease and soft rot. Follow the recommendations for well-drained and good air-porosity media, optimal fertility and slats management, as well as our preventative, four-component fungicide drench progra, addressing Rhyzoctonia, Erwinia and water molds.

Plant tubers 2" below surface, rounded side down. Tilting larger tubers slightly encourages drainage off the crown. The spacing of tubers in the field, raised beds or containers, depends on bulb size as well as whether they will be lifted in the fall.

The medium should be well drained and have a pH of 6-6.5. More drainage is required than for most cut flowers. Raised beds will aid drainage in heavier soils. When using soilless mixes, callas are most successfully grown in a 35-50% peat medium. The remaining perentage should consist of two or three parts of high draining materials such as coarse and graded perlite, fir bark, redwood shavings, vermiculate, lava rock or graded #2 or coarser sand. Sand also can act as ballast for top-heavy potted plants.

Recommended examples are:

1. 40% peat moss, 25% perlite, 10% vermiculite, 25% fir bark
2. 33% peat moss, 33% perlite, 33% vermiculite
3. 33% peat moss, 33% fir bark, 33% perlite

Trials with premixed media from leading brands indicate that media selection should be dictated by the need to hold peat levels down. Callas don't like 'wet feet'. Though luxuriant growth is promoted by higher peat levels (over 50%), the resulting moisture levels also promote pathogens.

Incorporation of gypsum and lime to the soil media is worthwhile not only for pH adjustment, but for calcium availability and its relation to plant health. Incorporation of a Trichoderma biological such as Root Shiled or Soil Guard at 0.75-1.0 lb/yd3 help disease management.

After planting, a complete wetting, followed immediately by a 3-component fungicide drench, is generally adequate moisture until the sprouts are emerged, especially in early, cool-season sowings. (Click here to see pesticide section on drenches).

Then, without allowing plants to totally dry, water only moderately at least until foliage is full. Even when growing rapidly, plants should neither remain constantly wet, nor should they dry out completely. Avoid splashing water to reduce disease spread. Proper water mangement is perhaps the most critical aspect of calla culture.

When planting early (Dec - Feb) in greenhouses, start in 70-75°F houses (or 70°F bottom heat) until well emerged. Temperatures can then be dropped to 60°F nights and 65-75°F days. Please remember that cool temperatures, overwatering and moist, heavy soil delay flowering and can promote diseases. Warmer temperatures can speed flower flowering. If temperatures are lower, reduce watering. Callas require minimum light of 4000-foot candles or more. Stouter stems and deeper coloration in pinks and many hybrid selections are achieved with high light and cool nights. Under high temperature and high light conditions, 30-50% shade will help growth and lengthen stems.

Preferred is a balanced, constant liquid feed at 100-200 ppm. Thse recommendations apply to the temperatures above. Available calcium sources, such as calcium nitrate, may be preferentially considered as a potential aid to disease tolerance. Slow-release fertilizers incorporated or top-dressed work well, but can release too quickly under warmer temperatures. Maintain EC levels of 1.5-2. Avoid EC levels of 2.5 or above. Leach media with clear water every 5th irrigation and especially during the last six weeks of production cycle.

Disease control and plant health:

Achieving or maintaining quality plants for the entire length of the crop requires cultural practices focusing on preventative control of diseases. Once established, diseases are difficult to control. Bulb stocks are filed grown and every effort is made to ship healthy bulbs. The aggressive bulb precondition for the Callafornia Callas is highly recommended and considered essential as the first step to disease prevention. SUccess in disease management is dependent on controlling three (3) primary pathogens that independently or in concert can cause root and/or bulb rot. These are Rhyzoctonia, Erwinia and the watermolds, known as Pythium and Phytothphora. Not one or even two products can successfully control all of these pathogents, and controlling only a portion of this pathogen complex can somethimes lead to worsening of the other untreated pathogens.

Product registration and availability vary by local, but our best recommendations or their alternatives must be followed to address each pathogen group. Media incorporation of the biological control Trichoderma is recommended as Root SHield @ 1 lb/ yd3 (460 gm/m3) or Soil Guard (Gliocladium is related to Trichoderma) @ 12 oz/yd3 (340 gm/m3). These are compatible with most fungicides and can help maintain healthy roots. Although less effective than incorporation, these biologicals can also be drenched at planting at 8oz/100 gal (60 gm/100 gal) but should not be used as a substitute for a preventative fungicide drenching. Use of Zero Tol (hydrogen diozide 27% ai) at a ratio of between 1:1000 and 1:3000 for algae growth in constant feed also helps manage pathogens.

The first fungicide drench is at planting, or perhaps even better at 3-4 days when planting "preconditioned" bulbs and initial watering. We recommend a multi-part tank mix, addressin the three pathogens independently.

Our best four-part tank mix chemical recommendations for drenches are as follows:
For watermolds, Subdue Maxx (mefenoxam 25.1% ai) @ 0.5-1 fl oz/100 gal (4-8 ml/100 L) and Aliette (fosetyl-aluminum 80% ai) @ 13 wt oz/100 gal (98 gm/100L);
For Rhyzoctonia, Heritage (azoxystrobin 50% ai) @ 4 oz gal (30 gm/100L)
For Erwinia bacterium, use Agrimycin-17 @ 8-16 wt oz/100 gal (60-120 gm/100L).

The above components have been found superior for the labels registered in California, but all may not be available in your region. Callas tend to be tolerant to cheimcal phytotoxicity. Trial other fungicides first on a small basis if these recommendations are not labeled in your locale. See our "Three Pathogen Calla Fungicide Drench Chart" below for these primary recomnmendations and other, lesser alternatives, should these not be available.

The Erwinia bacterium, leading to bulb soft rot, is best controlled with Agrimycin-17 (Streptomycin sulfate 21.2%ai) at 8-16 wt oz / 100 gal (60-120 gm/100L). Alternatives for bacterial control are few and, therefore, the standard Bulb Preconditioning using fized copper is essential. As drenches, these fixed coppers are root phytotoxic. Therefore, drenching of another agricultural antibiotic (at label rates) or use of soluble copper Phyton-27 (copper sulfate pehtahydrate 21.4%ai) at 13-20 fl oz/100 gal (100-156 ml/100L) can help. Please see chart for recommedations and alternatives.

Drench Timing:

Drench timing is critical. Drench the first time within 2 days of planting and no later than 4 days from initial watering. Timing of the second drench is important and should be made at 14-21 days after planting. A third drench is recommended for 21-28 days after the second one (day 40-47), but may only be necessary if weekly root inspections reveal cleared or browning roots.

If any of the above products are not available in your locale, then address the three major pathogens comprehensively with the best products available. Consult your local farm advisor. Callas tend to be tolerant of most products, and experimentation (and record keeping) with new products or combinations on a trial basis is encouraged. One such promising new product is the nutritional supplement potassium silicate, called Pro-Tekt (a Dyna-Gro product), which, in trials, has demonstrated immune supportive benefit.

Inspect Roots Weekly:

Inspect for cleared or browning roots and be sure to redrench as above if root problems are discovered. These chemicals will lose their effectiveness with time. The same is true of Trichoderma. For this reason, repeat drench with Trichoderma at 21-28 days and, if necessary, near day 42 as well.

Flower and Leaf Spot:

As leaves unfurl, watch for leaf spot, and, if present, spray foliage with Champ II (copper hydroxide 37.5%) at 1-2 qt/100 US gal (2.5-5.0 ml/L) plus Dithane (mancozeb) at 1 qt per 100 gal (see label). Reduce guttation leaf-tip water droplets by modifying greenhouse environment and ventilation. Guttation droplets can sometimes result in small necrotic spots due to salt concentrations along leaf margins, especially during times of high temperatures, overly dried media and excessive fertilizer release with temperature-dependent slow-release fertilizers, or a lack of the recommended clear-water leachings.

Sanitation:

Always remove diseased plants from the greemhouse or field area. Sanitation is critical, especially in multiple cropping programs, where rot can progress without an obvious cause. Between crops, sanitize bench, floor, conveyors,pots, soil mixers etc. Se also control of Fungus Gnats and Shoreflies below.

Insects:

C control aphids, thrips, shoreflies and fungus gnats (shoreflies and fungus gnats can spread bacteria; thrips and aphids spread virus): Orthene, Diazinon, Malathion, Tempo, Dursban, Maverik, Conserve, Endeavor and Marathon, for example, have been shown effective and non-phytotoxic. (Gnatrol and Exhibit are also very effective on fungus gnat larvae.) Check registrations in your area. Follow label rates. Callas tend to be tolerant to phytoxicity of most sprays. Do small trials on new chemicals

Pick flowers when the spathe is 3/4 to fully open and prior to pollen shed. Pollen shed usually occurs 4-7 days after flower is fully open.

Flowers can be picked either by pulling stems or by cutting stems. There are advantages and disadvantages to both techniques. Pulling stems increases stem length and is a much quicker technique. Place hand at base of stem and pull sharply. However, some research shows that younger flower primordia can be damaged this way and stem 'stretching' or bruising can take place if picking is not done correctly. Adequate soil moisture is necessary to avoid stem stretching when pulling.

Cutting stems reduces chance of flower primordia damage as well as stem stretching. However, the procedure takes more time, especially since the harvesting tool is to be sterilized between cuts to avoid potential spread of virus. In addition, the resulting stem length is slightly shorter.

It is up to each individual grower to decide which method is best for his or her operation. Most growers pull their stems.

After picking, the flowers should be recut and graded. They should be put in a solution of sugar and bactericide (chlorox) or flower preservatives. This will reduce stem splitting and post harvest diseases.

Flowers should be stored at 43-47°F (6-8°C) if possible. Stems should be recut and solutions changed every two days, if not daily. When bunching, do not bunch too tightly or solution uptake will be restricted.

* Growing information is provided courtesy of Golden State Bulb Growers.