Producing Million Bells – 2025 Update
Content contributions from Chevonne Dayboll.
With Million Bells (Calibrachoa) having filled up the greenhouse, it’s a great time to revisit our production practices and explore new ideas. This post contains some back to the basic’s information and new innovations for our favourite spring crop.
Nutrients
From a nutritional standpoint, the best thing you can is keep the pH of your calibrachoa in its ideal range; between 5.5 and 6.0. Not only can improper pH lead to stressed, lower quality plants but it can also impact disease susceptibility and further nutrient issues. A pH higher than the optimal range can inhibit nutrient uptake, especially micronutrients such as iron.
Iron deficiency can be difficult to distinguish from other issues (like Black Root Rot – see previous post), but iron deficiency typically leads to yellowing of new growth. Leaves may only show chlorosis between the veins, or it may be spread throughout the leaf. This is different from nitrogen deficiency where yellowing occurs in the oldest leaves. If iron deficiency occurs, adding a chelated form of iron is best for uptake. Choose your chelated iron form carefully, as different forms have different soluble rates which could impact its effectiveness.
Generally, calibrachoa is considered a heavy feeder. While that may remain true for its high iron requirements, as we learn more about the nutritional needs, 100-150 ppm nitrogen can be sufficient in the early stages of the crop. The key is to be consistent with fertilizer applications and to not overwater along with them. Feeding at a consistent lower rate may produce a paler plant, but you can “green-up” by applying a higher rate prior to shipment.
Promoting Optimal Growth
Spacing and growth habit
Million Bells like light and space. It’s important to give the plugs room to grow into a saleable plant. Fewer cuttings per container can result in the same desired plant if given the room to grow. Also, if you’re considering combining varieties in the same container, consider matching growth habit. No customer wants a basket with plants at two different heights! Since growth is highly dependent on variety, talk to your retailer about the recommended number of plants per container and matching combinations.
The concept of matching growth habit can be expanded to the greenhouse level as well. This recent article in Greenhouse Management outlines the art of strategic crop grouping in the greenhouse. If Calibrachoa plants are group with plants requiring similar pH levels, monitoring growth could be that much easier. Work smarter not harder!
Pinching
Traditionally, pinching has been thought to produce a better-quality finished product. You may pinch at the liner stage and wait for new growth before planting OR wait for un-pinched plugs to root in the finished container and then pinch.
However, a Michigan grower proved that by adjusting their PGR program or using LED lighting, pinching wasn’t necessary during the liner stage. Results showed that one low-rate application of Florel (ethephon) worked for 80% of tested varieties. For vigorous varieties, blue spectrum LED supplemental lighting for three weeks (with no PGRs) produced a great multi-branched liner. Read the full article here.
Plant growth regulators
The follow table is a list of recommended PGR’s for use on Calibrachoa. This table was adapted from Grower Talks PGR Guide for Annuals (2025-26). Before using any PGR products, it’s best practice to test and find a suitable rate on a few plants prior to treating the entire crop. Please read the full product label for recommended rates and potential phytotoxicity risks.
| Commercial Name* | Active Ingredient | Purpose |
| Dazide / B-Nine | Daminozide | Reduce internode elongation, resulting in compact growth habit |
| Citadel / Altercel / Cycocel | Chlormequat chloride | Growth retardant, resulting in compact growth habit (Note: chlormequat chloride and daminozide are often combined for applications) |
| Concise / Sumagic | Uniconazole | Reduce internode elongation, resulting in compact growth habit |
| Configure | Benzyladenine | Promote branching and increase flower set |
| Florel / Collate | Ethephon | Promote flower bud abortion and promote vegetative branching |
| Piccolo / Piccolo 10 XC / Bonzi / Pac O | Paclobutrazol | Growth retardant |
| Topflor | Flurprimidol | Growth retardant (Note: it is chemically closely related to ancymidol) |
Looking for help calculating your PGR mixes? Check out this PGR Mix Master calculator from E-Grow.
Getting Back to Basics. If you’ve ever wondered if different PGR’s with the same active ingredient result in different plant responses, check out this legacy Greenhouse Grower article Comparing PGR’s. In summary, the answer is NO! The experiments completed by Michigan State University researchers found little to no difference in efficacy of PGR’s with the same active ingredient.
Lighting
Did you know that OMAFA has conducted research on the use of LED lights in potted plants, including Calibrachoa? Check out the full article detailing LED research conducted by past Floriculture Specialist Chevonne Dayboll. The use of LED’s produced a similar size and flowering plant when compared to one’s grown under HPS.
Other Resources:
- Tips from an Ontario grower – Crazy about calibrachoa
- The STEM Podcast – Calibrachoa: From start to finish to sold
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