Greenhouse Canada

Features Crop Culture Inputs

January 29, 2008  By Melhem Sawaya

The production of bedding plants has dramatically improved in many fields over the last 10 to 15 years. The key to a successful crop? Have a planned, written program that you’ve developed and fine-tuned over the years, and have continually improved through experience and new information.

The production of bedding plants has dramatically improved in many fields over the last 10 to 15 years.

• Plug technology has changed the way bedding plant production and mechanization is handled, such as with seeders and transplanters.


•     The boom of vegetative material is changing the product mix, production and marketing of bedding plants.

•     Branding is influencing product mix, because brands are being marketed to the chain stores, largely bypassing the growers. This sometimes does not take into consideration regional differences, product culture or garden performance.

•     Advertising by buyers is geared to a specific date. This makes programming a crop very important to meet the sale date. The product is not accepted after that date.

•     There has been a definite shift in sales, with buyers now working with only one or very few suppliers for all their requirements.

With these changes and demands, producing bedding plants is a more detailed process. It also follows a specific production program. This program is more important than ever. We know that we deal with Mother Nature. We do not have control of some key factors, such as weather, but we must respond to the changes.

Here are some suggestions on how to stay on track, or get back on track, when unforeseen challenges arise.
Have a planned, written program that you’ve developed and fine-tuned over the years, and have continually improved through experience and new information.

Execute your program on time. My experience is that most of the mistakes that occur are not from lack of knowledge, but through not following your production program timeline.

Do not take shortcuts. For example, if a plant needs to be started at 18ºC to 20ºC and then cooled after 10 to 14 days, do so or else the crop will suffer and you’ll end up with inferior products or miss the sale date completely.
Know your planting media and water EC and pH before you start planting. Corrective measures after planting could be difficult to apply, and might have negative side effects.

Fertilize with every watering, not just once a week. Also, checking the soil EC and pH after planting is a must for optimum growth. The number one root disease problem is a result of high EC, or drying up the crop too far with EC levels in the upper range. No other practice is better than consistent moisture levels with continuous fertilization, and EC and pH reading and adjustment. Most of the time when we drench with a fungicide, all we are doing is lowering the EC levels and then the plant will recover. This makes us believe the chemical is doing its job.

Do not transplant any material that does not look healthy. It is best to try to recover it in the liner or plug stage, or discard it if the plant is not recoverable. This is the stage where you can reduce your losses.

In my experience, there is not one crop you plant and start really cool (that is, below 16ºC). It is always good to start crops at 20ºC and then cool gradually.

Know which crops can finish cold and which cannot. Cool the ones that can take the cold by all means, but remember to add growing time to meet shipping dates. Some crops should never be grown cold, including ipomea, angelonia, salvia, celosia, vinca, and hibiscus (tropical or perennial).

Growing plants too dry does not set buds, but slows vegetative growth resulting in plants that might have flowers but on a smaller plant. Caution: over-drying plants will abort buds and the cycle of setting the bud will have to start again. For example, wax begonia is a crop that does not readily show a wilting effect and is a prime example of flowering delay due to over-drying.

Use growth regulators properly and at an early stage. Not one growth regulator will shrink plants. New growth regulators are available and there are now new ways of using the old ones. Familiarize yourself with these techniques, trial them, and put them into practice.

Know how to manipulate temperature with light levels. On average, lower the temperature by 5ºC to 7ºC on real cloudy days, especially if the crops are grown under a canopy of hanging baskets. A combination of low light and high temperatures is a guaranteed recipe to stretch weak plants.

Manipulate crop time with cool temperatures to slow crops down, but lower the humidity at the same time, especially at night. Botrytis grows the best at 17ºC with high humidity levels, so lowering temperatures to 14ºC will increase humidity if we do not vent. But it will not speed the spreading of Botrytis. So lower temperature and minimal venting will buy you time for slow sales or early crops.

Fertilize all the way until the sale dates. Stopping early will lower the quality of the product. At the same time, your target EC in the soil should be lowered to 0.6 mmho two-to-one, water-to-soil testing.

 Use the different types of fertilizers to your advantage. Make sure there is phosphorous in your formula, but at a low rate. Many articles and books suggest that phosphorous stretches plants, which is true, but the lack of phosphorous will cause yellowing and poor plants (if not dead ones).

High levels of potassium to finish crops is recommended, which helps in two ways:

a.)     Potassium ensures brighter flowers.

b.)    It slows down the plant’s uptake of water, which makes the plants more compact.

Clear water stretches plants, but a fertilizer with high potassium, calcium and magnesium, and with lower nitrogen and a basic amount of phosphorous, will finish healthy plants.

Apply sprays for spider mites and aphids at early stage to avoid flower burn at sales time. Also, remember to treat for powdery mildew on susceptible plants, such as verbena.

Last but not least, remember the LALA theory of looking, asking, listening and acting. For me, it still proves to be the only way to improve and get ahead. If we want to change the output, it is not going to happen on its own. We have to change the input. Prosperity and progress only happen by change with a vision.

Melhem Sawaya of Focus Greenhouse Management is a consultant and research coordinator to the horticultural industry. Comments on this or any other article are always welcome by e-mailing me at

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