Greenhouse Canada

Features Crop Culture Inputs
Growing Points: Working towards a top crop

September 23, 2014  By Dr. Mohyuddin Mirza

Three decades ago, I took a management course and one statement is still stuck in my mind.

Three decades ago, I took a management course and one statement is still stuck in my mind. The instructor asked, “which is the biggest room?”


I thought it was my bedroom; another participant thought it was a mushroom; and others offered their choices. The instructor said none of our answers was correct, adding that the correct response was “room for improvement.”


While looking back at this year’s spring season, I thought there was a big room for improvement in the case of bedding plant production, beginning with suppliers and continuing through to marketing.

This year’s season was very unusual. Beginning with planting in late-February and continuing through to retailing in April and in May, the clouds, rain, snow and wind caused a great many plant-related issues. (I reported on some of them in the June issue of Greenhouse Canada.) I received so many emails and phone calls that it appeared that every grower had some issues.

This forced me to examine some growing practices – especially those of smaller growers who are just seasonal in nature. In many cases, the issues were with supplies, and in other cases it was related to the grower’s management practices.

Symptoms of Tobacco Mosaic Virus (TMV) were seen on some petunia varieties. Suppliers were proactive in resolving the issue and some unrooted cuttings had to be destroyed. Some growers were left without their favourite colours for customers. Growers were concerned with how TMV could spread to other plants. Decision-making was tough, because samples had to be sent to a lab, and it sometimes took a few days for the results.

This is what the symptoms looked like in one variety (see above). The lab tests, however, were negative for TMV in this case. The breeder thought it was likely a “chimera” problem – a genetic condition where new growth can show different colours or patterns due to mutations.

Some petunia plants had positive TMV results. I noted that many growers were reluctant to talk to suppliers because they thought it was their “fault.”

When growers did call their suppliers, they were often told they were the only ones reporting this problem. This made them feel even more “guilty!”

I think the attitude that you are the only one to have this problem is not a good business practice.

Some suppliers and propagators, however, were more helpful and quickly took responsibility and ownership of the problem and came up with solutions.

Many growers observed that some bags of a commercial growing medium were giving off a rotten odour when opened, and the E.C. was quite high. I monitored those bags and confirmed that E.C. was over 6.0 mmhos in some cases. The plants grown in this growing medium did not dry out as plants did in other bags, causing the waterlogged conditions.


This pot was not watered for over two weeks. The plants did not become established and soon rotted. Fungus gnats and shore flies love this situation. The practical implications for such a situation were that plants were damaged, some died, and they had to be discarded. If water cannot be supplied to a plant, it means we cannot give nutrients either, and the chance of waterlogged conditions arise.

Tomato Spotted Wilt Virus was seen on pansies (photos below), and there was clear evidence of thrips feeding. This virus is transmitted by thrips. Control strategies include getting rid of thrips at an early stage of plant growth. Similar spots due to this virus were seen on calibrachoa.

6288-Photo-3-shows-tomato 6288-Photo-4-shows-more

I took these pictures during the peak season in May and noted the different types of greenhouses.


The picture on top was taken in a greenhouse where the sidewalls are about 21 feet in height and hanging baskets are “truly” hanging. There is not much shade on the plants grown below.

The picture lower left shows a greenhouse with sidewalls of about 15 feet in height. The baskets are geometrically placed so that light penetration is reasonably good.

The sidewalls in the last picture are about 12 feet tall and too close to the plants below. One can clearly see shade on geraniums being grown below the baskets.

With this kind of plant density, when weather becomes cloudy and rainy for a few days and growers don’t reduce the day temperature and are not able to move enough air, many physiological and pathological problems arise. (I just checked a catalogue, and, incidentally, there are over 584 types of plants grown in bedding plant greenhouses!)

The plants stretch and become leggy and lanky. “Lanky” is a term I use to describe the following picture of pansies and petunias.


The cells in the stems are full of water, have not matured and therefore will be poor in quality. Pansies can easily be hardened off in cold frames and I have seen nice, very compact plants ready for planting outside. The picture at right, previous page shows how petunias reacted to warm temperatures on cloudy days with high relative humidity.

This is an extreme example (photo above) where consistently high relative humidity levels caused algae to grow on sidewalls. There were plenty of fungus gnats and shore flies in this greenhouse.

I also found that growers with smaller greenhouses have the simplest possible fan and heat controllers. In many cases, the growers don’t change the day and night temperature settings because it has to be done manually. The plants were growing at 21 C day and night. In one case the grower was using cooler day and warmer night temperatures! It appears that the grower misunderstood the recommendation.


The night setting should be a few degrees cooler than the day temperature because they require those conditions at nighttime … and it saves energy as well!

There is still room for improvement in environmental controls for bedding plant growers, especially for smaller growers.

Dr. Mohyuddin Mirza is a greenhouse consultant. •

Print this page


Stories continue below