Guidelines for Growing in Pots

Highest quality and uniform calla culture requires special attention to media selection, water management and forcing temperatures as well as a preventative fungicide program. Please read and follow these entire directions carefully.

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*.

1. Order pre-treated tubers. If not, follow new recommendations for disinfectant and GA spraying.
2. Sort and air dry bulbs before planting.
3. Plant with only 1 to 1 1/2" of media covering the tuber.
4. Use well-drained media with good porosity. Incorporation of Trichoderma biologicals is beneficial.
5. Follow optimal temperature regimes by stages.
6. Follow proper water management recommendations.
7. Follow fertility recommendations and avoid ammonium forms of nitrogen.
8. Plant growth control and Bonzi require special considerations and record keeping.
9. Drench immediately after planting with chemical combinations mentioned
10. Redrench with our recommended strong preventative program, day 14-21 (pre-Bonzi) and again day 40-47.
11. Maintain greenhouse sanitation.
12. Control fungus gnats, shoreflies and chewing larvae.

Pre-treated tubers:

Pacific Callas highly recommends the order of pre-treated tubers. Pre-treatment enhances flowering and aids in disease prevention, and saves growers considerable handling. Standard gibberellic acid, Progibb (GA3) or Provide (GA4+7) or Promalin (GA4+7 with benzyladenine) treatments increase the total number of flowers per tuber. Generally you can expect twice as many flowers with a GA treated tuber than with an untreated tuber. GA will slightly increase plant height, slightly reduce leaf width and soften tissues, especially in low light and shorter days and in combination with high N fertilizer. Subsequent Bonzi application minimizes these effects. Most growers request that their calla bulbs be pre-conditioned prior to shipment. This saves growers considerable handling, reduces disease and justifies the small additional charge.

Non Pre-treated tubers:

For non-preconditioned tubers, GA plus fungicides may be applied to tubers with a backpak sprayer. Avoid tank dipping to reduce possible pathogen spread. If you purchase calla bulbs that have not been pre-treated, your tubers should be sprayed with a fixed copper solution of copper hydroxide 37.5% (Champ II flowable) at 3 Tbsp/U.S. gallon (20 ml/L). Copper oxychloride 50 wp at 0.4 oz/U.S. gallon (3g/L) plus Promalin at 100 ppm also works, as does GA3 (Progibb) at 125 ppm.

GA should be added to the spray mixture at the following rates:

• 1.8% Promalin solution: a 100 ppm GA 4+7 +BA mixture is 1.3 Tbsp per U.S. gallon H20 (5.5 ml/L).
• 4% GA3 solution (Progibb): a 125 ppm mixture is 0.8 Tbsp per U.S. gallon (3.1 ml/L).

For dipping, reduce Promalin to 75 ppm or GA3 to 100 ppm. Adding a fixed copper disinfectant to the GA solution will help control pathogen spread and reduce soft rot. The mixture must be agitated regularly. Allow to air dry, without fanning, over several hours for full effectiveness of the materials prior to planting.

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 a couple of days prior to planting. This will insure that any possible friction wounds caused by transit are well callused before planting. For long-term storage (6 weeks or more), keep well ventilated at 50°F and a relative humidity of 80%.

The number of days between planting date and bloom decreases as the planting date is moved later in the year. Warmer temperatures and longer days accelerate growth. When potting callas October-December, the earliest and darkest plantings in the northern hemisphere, plan on 2-3 weeks more bench time to reach peak bloom. For such sub-optimal conditions, plan on using additional Bonzi, maintaining cooler finishing temperatures and optimizing available light. With no exact scheduling perected, some approximate averaged forcing times follow.

Please click here to view a chart showing the average forcing times of most varieties.

Plant with 1 to 1.5" of media over the tuber, rounded side down, sprouts (eyes) up.

Pot sizes below 4.5" standard are more difficult to grow due to root volume restriction (especially in clay pots). Additional care and management of fertility and irrigation are required in small or shallow pots because plants tend to be weaker, more easily stressed and therefore, more disease prone.

Please click here to view a chart showing the recommended planting densities for producing good quality pots.

The medium should be well drained, with a pH of 6-6.5 and have good air porosity (optimum porosity at 20% +/- 5%). Peat basted media should use a coarse grade and me in the range of 30-50% of the mix. Lighter formulations, using less peat, are suitable for cooler, early winter plantings. Higher proportions of peat are sometimes used by experienced growers, but at the risk of enhancing diseases.

Additional well drained components include, but are not limited to, graded large particle perlite, sand, firbark, pumice or scoria. Redwood sawdust should not make up more than 30 % of a mix. Pink bark is known to tie up Bonzi variably and should be used with care or avoided.Graded #2 sand can help ballast pots on taller varieties. Incorporation of gypsum/lime will help not only pH balance, but provide calcium for good plant health. A light two-week starter charge of a balanced fertilizer will help plants get off to a fast start.

When mixing media, care must be taken not to over-grind components. The resulting reduction of particle size in such media will reduce aeration to the point of favoring root pathogens.

We recommend incorporation of Trichoderma biologicals such as Root Shield (1 lb/ yard3) or Soil Guard (12 oz/yard3) into the media 3-7 days before planting to promote optimal root health.

Sample media: 3 part coarse peat: 2 part large perlite: 2 part 1/8 - 1/4" firbark: 1 part #2 graded sand (optional for ballast).

The bacterial soft-rot syndrome, which concludes with Erwinia cartovora, is generally preceded by water molds and Rhizoctonia. Other wounds or stresses also add to this profit-impacting pathogen complex. It is very important to follow media recommendations, use good sanitation practices and prower water, preventative drench and temperature management. In early forcing, most calla diseases are facored 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 are recommendations for well drained and good air porosity media as well as our preventative, three-component fungal drench program, addressing Rhizoctonia, Erwinia and water molds.

Optimal environment involves good air circulation, moderately high relative humidities and the highest possible light (only in hot and bright summer forcing conditions will 30-50% shade be necessary). High light yields more compact plants and reduces the need for Bonzi. Consistent temperature regimes for each stage and avoidance of temperature extremes greatly enhance plant performance and health.

Recommended temperatrues are stage dependent:

Please note that cooler temperatures will improve plant habit and reduce, or even elimiate Bonzi requirements but will lengthen bench time as well as increase water retention in the media. Temperatures of 50°F and below start to arrest calla growth.

The only way to speed bloom in callas is to increase temperatures. But, warm temperatures, especially under low light, will produce taller and softer plants. So, for timing your crop, it is better to plant early and slow it down with cooler temperatures than to plant late and have to add heat in Stages 2 and 3.

Horizontal air flow, usually by fans hung in series around the greenhouse, is important in creating a non-stagnant and uniform plant environment throughout. Overly dry conditions reduce leaf widths, lessen general fullness and vigor and can even imact number of sprouts. Conversely, constant and overly humid (and excessively hot or cold) conditions can favor foliar diseases and root diseases, especially with no horizontal air flow.

Water management is critical. Keep pots moist but avoid excessively wet and excessively dry conditions. The first (within 4 days of planting pre-conditioned tubers) thorough watering should be a three-part preventative chemical drench. Then, water sparingly until leaves unfurl. Between days 14-21, do a second chemical drench.

Pooling and splashing will spread disease. For this reason, ebb-and-flood systems can be risky. Alternate extreme dry then extreme wet conditions will cause root injury and will greatly increase pathogen susceptibility, especially if slow-release fertilizers are used in warm conditions. The addition of Zero Tol at 1:1000 to 1 3:000 for algae control is compatible with, and recommended for, forcing callas as it assists n disease management.

Good quality water at an E.C. below 1.5, sustains plant quality, growth and overall plant health. High salinity or other water problems should be treated.

The ideal starter fertilizer precharge would be a 10-20 day soil incorporated application of N-P-K at approximately 15-3-15 (plus minors, if possible). Keep pots moist and E.C. levels between 1.5-2.0. Avoid E.C. levels above 2.5. It is best to avoid ammonia forms of nitrogen. We recommend growers use a constant 150-200 ppm balanced liquid feed which includes minors. Reducing the concentration in low light or poor growth conditions is advised. Uniform incorporation of slow-release or other granular fertilizers can be difficult, but can be done in indicidual pots by using approximately a 1.5 gram (1 tsp) of 15-3-15, well mixed into a 6-inch pot. Slow-release charges over 30 days tend to induce leaf marginal salt burn if temperatures rise to above 78°F and if pots dry excessively. Supplementing the media with 3 lbs. each of lime and dolomite per yard can provide calcium for plant quality and disease tolerance. Keep climate, growth and fertility records for future reference. Leach pot salts with clean water every fifth irrigation start to finish, especially during the last 6 weeks and especially if producing small pots.

Bonzi (paclobutrazol @ 0.4%ai) is the most effective growth regulator and plant 'toner' or 'toughener.' The individual grower's product objectives and environments must also be considered in Bonzi use. Factors other than concentration (ppm) greatly influence Bonzi efficacy. As Bonzi use is an art as well as a science, take notes on your encironmental conditions (media moisture at time of appliation, temperature and light conditions post application, etc.) in order to achieve repeable results next time.

Apply Bonzi when all sprouts have emerged and are between are 0.5 to 3" tall. Pots must be uniformly moist. So, it is best applied a day or two after an irrigation or the second fungicide drench. Segregate pots by sprout size, treating tallest pots first. Then, when slower pots reach 0.5 to 3" sprouts, drench these pots also. Second and subsequent applications are usually made 6-10 days after the preivious one. Do not treat after 40 days post emergence. Too much Bonzi will reduce flower counts. However, Bonzi use will greatly improve post harvest shipping quality. Slightly higher rates are favored for shipping longer distances.

Use caution if and when "injecting" Bonzi. Better yet, avoid using injectors to apply Bonzi. Paclobutrazol is a very effective and persistent PGR. Therefore, a small deviation from your desired rate may lead to substantially varying results.

Since injectors are prone to deviate and or drift from the setting shown (i.e., 1:200), regular maintenance and calibration of injectors is essential to successfully "inject" your Bonzi. Additionally, keep in mind that the Bonzi concentrate will be pulled from the concentrate tank in the form of a "pulse" or a "dose". Without the use of a blending tank, your crop will receive varied rates of material. Ultimately, injectors will serve growers best in the roles of delivering fertilizer and/or fungicides, where deviations from rates are often more tolerable.

Our recommendation is to prepare a tank-mixed, final solution at your desired Bonzi rate, while using a portable sprayer. This method will allow you to deliver precisely the desired rate of Bonzi from a diluted, ready-to-apply volume of solution (i.e., 10ppm = 0.33 oz/gallon; or, 33 oz Bonzi/100 gallons water).

Spray Tank Method: Remove nozzle tip from wand and reduce pressure at regulator. Test fill a measuring cup to determine "trigger pull" rythm for approximate dosing (4 oz solution/4" pot; 6 oz solution/6-6.5 inch pot). Our best recommendation is to use metering system for gar greater dosing accuracy.

Please see individual variety pages for specific recommendations regarding how much Bonzi to use by variety. Our conditions suggest we use 8-10 ppm (1/4 - 1/3 oz/gal or 2.5-4.0 ml/L) on "x-low" and "low" use varieties and 10-15 ppm (1/3 - 1/2 oz/gal) for "medium" and "high-end" use varieties. Your experience and conditions may lead you to use different rates. In general, we recommend repeat applications at low concentrations (8-15 ppm) rather than single (or fewer) applications of higher concentrations.Note that solution volume per pot is as critical as ppm because Bonzi is trapped in the media and becomes concentrated if liquid is applied past runoff. A metering system is therefore advised. The above rates are based on moderate California light levels. We suggest drenching 6 ounces per 6-inch pot (177 ml per 15 cm pot) and 4 oz [er 4 1/2" pot (118 ml per 11 cm pot). Note: Certain media components such as pine bark can tie up Bonzi and reduce its effectiveness.

The plants must be actively growing for Bonzi to be taken up by the roots and assimilated. Cold dark conditions post application will greatly reduce Bonzi effectiveness. Keep your environment stable and within the recommended temperatures for consistent and replicable results. Keep good records.

Slightly cooler temperatures in Stages 2 and 3 and high quality greenhouse coverings will also improve plant habit and tone. Factors reducing plant habit quality (causing weakness and stretching) include low light or short light hours, long periods of far red light (twilight), excessive nitrogen, high temperatures, plant crowding and poor ventilation.

Disease control and plant health:

Achieiving or maintaining quality plants for the entire length of the crop requires cultural practices focusing on preventative conrol of diseases. Once established, diseases are difficult to control. Bulb stocks are field grown and every effort is made to ship healthy bulbs. The aggressive bulb pre-treatment is recommended and we consider it essential as the first step to disease prevention.

Success in disease management is dependent on controlling three primary pathogens that independently, or in concert, can cause root and/or bulb rot. These are Rhizoctonia, Erwinia, and the water molds, known as Pythium and Phytothphora. Not one or even two products can successfully control all of these pathogens, and controlling only a portion of this pathogen complex can sometimes lead to worsening of the other untreated pathogens. Product registrations and availability vary by locale, 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 at 1 lb/yd3 (460gm/m3), or Soil Guard (Gliocladium is related to Trichoderma) at 12 oz/yd3 (340gm/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 (60gm/100L) but should not be used as a substitute for a preventative fungicide drenching. Use of Zero Tol (hydrogen dioxide 27%ai) at 1:1000 to 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 after initial watering, but do so only if using "preconditioned" tubers. We recommend a multi-part tank mix, addressing the three pathogens independently.

Our best four-part tank mix chemicl recommendations for drenches are: for specific water-mold control is a Subdue Maxx drench (mefenoxam 25.1% ai) at 0.5-1 fl oz/100 gal (4-8ml/100L) or alternatively with Aliette (Fosetyl-aluminium 80% ai) at 13 wt oz/100 gal (98 gm/100L); for Rizoctonia, Heritage (azozystrobin 50% ai) @ 4 oz/100 gal (30 gm/100L); and for the Erwinia bacterium, use Agrimycin-17 @ 8-16 wt oz/00 gal (60-120 gm/100L). The above components have been found superir for the labels registered in California, but all may not be available in your region. Please see our "Three Pathogen Calla Fungicide Drench Chart" below for these primary recommendations and other, lesser alternatives, should these not be available. Callas tend to be tolerant to chemical phytotoxicity. Trial other fungicides first on a small basis if these recommendations are not laveled in your locale.

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, our standard bulb pre-treatment using fixed 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 pentahydrate 21.4% ai) at 13-20 fl oz/100 gal (100-156ml/100L) can help.

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 and hopefully just a day or two before or at the time of Bonzi application (provided Bonzi is applied within this 21 day period). A third drench is recommended for 21-28 days after the second one (day 40-47 from planting), but may only be necessary if weekly root inspections reveal cleard or browning roots, any diseased plants, or if poor or prolonged shipping environments may be expected.

If any of these 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 we encourage experimentation (and record keeping) with new products or combinations on a trial basis. One such promising new product is the nutritional supplement pottassium silicate, called Pro-Tekt ( Dyna-Gro product). In our trials, it has demonstrated immune supportive benefit.

Inspect pots weekly 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 redrench with Trichoderma at 21-28 days and, if necessary, near day 42 as well.

As leaves unfurl, watch for leaf spot, and, if present, spray foliage with Champ II (copper hydroxide 37.5%) at 1-2 qt/100 gal (2.5-5.0 ml/L) plus Dithane (mancozeb) at 1 qt/100 gal (2.5 ml/L) or Chipco 26019 at 1 lb/100 gal (1.2 g/l). Reduce guttation leaf-tip water droplets by modifying greenhouse environment and ventilation. Guttation groplets can sometimes result in small necrotic spots due to salt concentrations along leaf margins, especially during times of high temperatures, overly dried pots and excessive fertilizer release with temperature-dependent slow-release fertilizers.

Always remove diseased plants from the greenhouse. 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.

Control of Fungus Gnats and Shoreflies is important due to their ability to spread bacteria and disease. Generally, callas are relatively tolerant to phytotoxicity of foliar sprays, and label rates of most insecticides can be used safely. Controls on an as-needed basis for white flies, aphids and thrips are recommended. Early leaf-chewing evidence by larvae after sprouting requires an insecticide drench as soon as possible. Control thrips as they can rapidly spread the foliar viruses INSV (Impatiens Necrotic Spot) and TSWV (Tomato Spotted Wilt). Control aphids as they can spread DMV (Dasheen Mosaic Virus). Always watch for Erwinia infected plants and carefully remove and discard.

* Growing information is provided courtesy of Golden State Bulb Growers