Cooling our Glasshouses in the Hot Summer Sun

Today it’s 32° C (89.6° F) in Mississauga, and the Weather Channel says that it feels like 39° C. In Hungary, 500 elderly people died last week when the mercury reached 42° C (107.6° F). Yeah, summer can be a killer!

The heat can kill Roses, too. We’re using every trick in the book to cool our three Glasshouses, but pretty soon we won’t have a choice. We’ll have to install air conditioning systems in each and every one of them.

It’s not just the ambient temperature of the air that we have to worry about. The temperature of the reservoir can determine whether our flowers will thrive or stop all growth and bud production.

As you know, we use a multi-bucket ebb and flow hydroponic system to grow all our Roses, and our reservoirs are contained in stainless steel tanks. Everything is state of art, smooth for easy cleaning, and equipped with chillers to keep the rez temp down.

The temperature of the nutrient solution is just as important as the pH or the parts per million of dissolved solids. Pedro still goes around daily with his truncheon EC and pH meters, as well as a digital thermometer, to make sure that the rez temp doesn’t go above 80° F. Actually, it’s best between 65 and 75° F (18.3 to 23.8° F).

In hot, humid Mississauga during the dog days of August it’s not possible to use some of the methods suggested by Pedro. It seems that his Rose-growing family in Spain has used the high pressure fogging method, combined with heat expellers. This method will not work effectively in hot, moist climates, like ours.

Most North American greenhouses use pad-cooling with pressure-less watering and air exhaustion. Huge pads made of various absorbent materials are hung along one side of the Glasshouse, over open air vents, while the other side of the Glasshouse has large, slow-moving fans sucking the exhausted, hot air out of the greenhouse through appropriate openings.

The pads are soaked with pressure-less water. Due to the exhaust fans having created suction, hot air from the outside enters through the pads and thus is cooled and humidified. Since our air is already humid, this isn’t the perfect cooling solution, either.

With high humidity come eager fungi ready to attack our Roses. Pedro is spraying religiously with Scorpion Juice every Sunday, then with Piranha on Wednesdays. The former is like an inoculation, imparting induced systemic resistance against many pathogens and pests, while the latter spreads beneficial fungal spores all over our plants.

Sort of like fighting fire with fire, spraying fungal spores actually does help prevent fungal infections, since the mycorrhizal fungi in Piranha fight off and prevent fungal infestations by such bad guys of the fungal world as Fusarium, Rhizoctonia solani, Pythium, and that all time dread, Gray Mold (Botrytis cinerea).

Up until the second week of flowering, Pedro also sprayed with Protector. Once the blooms mature, however, this Advanced Nutrients product cannot be used, since the active ingredients that combat Powdery Mildew might also interfere with floral growth and coloring.

Now that the heat is so high, I suggested to Pedro that we fill plastic bottles with water, deep freeze them, then put them into our reservoir to keep the temperature down. Ice is by far the best cooling agent. The chillers do their job up to a point, but even they need all the help we can give them.

In the weeks of bloom when the Nutrient Calculator calls for application of Piranha, Tarantula, and Voodoo Juice into our nutrient mix, it is especially important to keep the temperature of the mix down. Mixing these products in hot water can kill the beneficial microorganisms they contain and render them ineffective.

In fact, most of the products in the nutrient mix should be mixed at room temperature, perhaps with the exception of Barricade, which is slow to dissolve and should always be mixed in the night before, to give it a chance to blend in better.

Barricade is a potassium silicate product that thickens the cell walls of our Roses and thus it makes them less vulnerable to parasitic attacks of different kinds. Not only do microorganisms such as viruses, bacteria, and fungi hesitate and are kept from attacking our prize plants, but even insects find it hard to get their sucking mouthparts through the thicker cell walls built up by Barricade.

I put Pedro to work researching large capacity air conditioning systems. The York company, which makes air conditioners for many of the world’s tallest buildings, also makes a system that is perfect for Glasshouses.

If global warming raises our summer temperatures another five degrees, we’re going to have to spend the money on such a system for each of our Glasshouses, in order to protect our overall investment in the exquisite Hybrid Tea Roses that grow in Red Rose, Blue Rose, and Multi Rose—our pet names for the three structures that house our ornamental grow op.