Growing Calibrachoa Successfully

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Calibrachoa Superbells Coral w Red Eye

The explosion of new breeding in calibrachoa is likely one of the fastest our industry has ever seen. Each breeding company’s offerings come from a slightly different breeding focus, so there is great variability between series on the market. For most breeders, the goal is either grower performance or consumer performance, and there’s a big difference between the two. Based on the weaknesses of the original plants from Latin America, most programs focus first on disease resistance and avoiding sensitivity to pH, since these are two of the biggest problems the crop faces. Having hopefully dealt with those two issues, breeders then focus on plant habit and flower color in order to complete a series or collection.

Calibrachoa has some wonderful qualities that make it different from petunia. One of the things most people notice first are the unique colors and patterns, but plants are also well-adapted to very high light levels, excellent for hanging baskets and extremely tolerant of dry conditions. This last is an important survival trait once plants make it to the consumer. Each breeding company will offer some regional differences due to where their plants are bred and selected before release. Plants bred in colder regions often don’t have as much heat tolerance, and plants bred for heat tolerance can be somewhat less able to deal with early-season cold greenhouses and wet soil conditions. Each grower needs to experiment and decide what works best in his or her location.

High Light, Lower pH And Careful Watering Are Keys To Success

When some basic guidelines are followed, growing calibrachoa is easy; the guidelines are the same for all series. The key factors to focus on are providing high light levels, avoiding overwatering and providing good air circulation. The genus calibrachoa comes from the rocky hillsides of Brazil for the most part, so that is a good indication of the growing conditions the plants prefer. They need excellent drainage, love sun and do best when the air is moving within the greenhouse.

Watch your watering and apply a fungicide when transplanting: This is where a lot of growers get into trouble, especially in the north. Early-season production means low light levels, a cold greenhouse with the soil staying wet for long periods, and usually a closed greenhouse with low internal air circulation. It is a recipe for having problems with the crop. Most companies know growers will bring material in early and face these potential issues, so they all recommend a fungicide drench at transplanting to help counter the disease risks of a cold, slow-growing crop. That fungicide drench should be required for most growers, because of the number of problems the industry sees with early season production. These problems are even more frequent when the spring runs long and dreary. Protect yourself with a fungicidal drench when transplanting.

Understand how your soil pH impacts growth. Maintaining proper soil pH is critical. All series do best when pH is kept between 5.5 and 6.0. It is okay to let the pH go a bit lower, and most can tolerate a pH as low as 5.0. It is when the pH gets too high that growers run into problems. At higher pH (above 6.0), the plant loses its ability to pick up iron from the soil, so the first signs of high pH are yellowing and chlorosis. If this goes on too long, plants will lose vigor, have reduced branching and begin to decline. The key is maintaining pH below 6.0 to 6.5. Additional foliar iron can be applied if the problem is caught early enough, but unless you fix the soil pH, you’ll be fighting the problem all through the crop.

Guidelines For Growing Calibrachoas Successfully

Optimal pH is between 5.5 and 5.8.

Optimal EC (or soluble salts) using 2:1 Extraction Method: 0.6 to 0.9

Fertilization Recommendations: 150 to 200 ppm at transplant then shift to 200 to 250 ppm in production. Higher feed rates increase early growth, but use a stronger level of feed rather than watering and feeding more often in order to avoid overwatering. Use a balanced fertilizer with no more than 25 to 30 percent ammoniacal nitrogen. Reduce ammonium levels if you are starting to get too much stretch. Check your water quality with a trusted lab and use fertilizers based on your water quality. Most calibrachoa benefit from elevated levels of iron in their fertilizer (1 to 2 ppm).

Growing Temperature: 55°F to 65°F (13°C to 18°C); plants can be grown cooler but it extends finish time. A negative DIF to finish the crop by running days at 55ºF and nights at 62ºF to 65ºF can also keep plants compact. This will improve overall crop quality. Most calibrachoa can be brought into colder conditions once they have gotten a good root system started. Hardened-off plants can be brought outdoors in the spring months. As long as they hardened off, most calibrachoa can tolerate a mild frost +/- 28ºF.

Light Levels: Always High (+ 5,000 ftc) to promote compact growth and to accelerate natural branching capabilities. Superbells do best in full sun inside the greenhouse and outdoors.

Water Requirements: Average, but if in doubt, allow plants to dry slightly (do not dry to wilting stage). Remember these are native to cliffs and rocky slopes and require excellent drainage. Be very careful of overwatering, especially under cold, low-light conditions. Begin allowing the media to dry between irrigations once the roots have formed through the new mix. It is imperative not to overwater plants once they have established themselves in the new media.

Planting And Timing Information: Most flower by week 9 to 10, so plan accordingly.

Finish Time:

  • 4- to 5-inch pots: 4 to 6 weeks
  • 6-inch/gallon pots: 5 to 7 weeks
  • 8-inch pots: 7 to 9 weeks
  • 10- to 12-inch pots: 10 to 12 weeks

Pinching/Growth Regulators: For pots 6 inches and smaller, pinch at transplanting. Or, a single spray of Florel at 500 ppm can substitute for no-pinch on the 4.5-inch pot size. For hanging baskets and pots larger than 6 inches, soft pinch at planting and trim around the pot just prior to hanging. A 5 to 10 ppm Sumagic spray or a B-Nine/Cycocel spray (2500/750) tank mix spray also works well. A 500 ppm Florel spray on baskets and larger pots will promote branching. Growers in the South and Southwest may need slightly higher rates due to warmer production conditions.

Pest And Disease Management: As with all crops, begin each season with fresh, sterile growing medium and start with a clean, disinfected greenhouse. Disinfectants such as bleach, Greenshield, and ZeroTol are all effective. A preventative drench at planting with broad-spectrum fungicide is a great idea. The most common cause of problems with calibrachoa is overwatering.

Calibrachoa are sensitive to Pythium, Phytophthora and Thielaviopsis. Superbells have higher levels of tolerance to these diseases than other calibrachoa, however, maintaining proper pH (5.5 to 5.8) and good sanitation practices will help alleviate problems. Increased air circulation, proper water management and good soil porosity are also critical. Scout regularly for aphids, which can be problematic. Be sure to check hanging baskets that are hanging high. It can be easy to forget to scout for insect problems with pots high in the rafters.

Fungus gnats especially, and aphids secondarily, are the most common pests of calibrachoa. Fungus gnat larvae can be devastating as they can burrow up stems and cause plant collapse and death or weaken the plants, making them susceptible to disease. Do not allow standing water or algae to form on floors, tables or media. A potato wedge placed on top of the media is a good way to check for larvae populations. Control moisture in the media and use larvaecides to suppress any larvae populations.

Thrips are most prevalent when blooms are forming. Control populations prior to introducing the crop.

Growing calibrachoa is easy, but you need to carefully monitor your pH, avoid overwatering and grow a clean crop. Avoid the early season syndrome of poor light, poor air circulation and soggy media. You can fertilize at higher levels and reduce watering to make sure plants get the nutrients they need but not the excess water from repeated watering. If one of your growers is a wet grower, work with them to avoid problems on a calibrachoa crop.

Once the season is underway and light and temperatures go up, most people stop having any problems with this crop. The problem becomes having enough of this incredibly popular and dynamic annual. Plants grown well from the start will generate better profits and fewer headaches, so just follow these simple rules and plan ahead for next year.

Rick Schoellhorn is director of new products at Proven Winners. You can e-mail him at rick@provenwinners.com.

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