Home > Begonian > Volume 69 (September/October 2002)

How I Handled the Heat of the Summer of 2001
by Dale Sena

Located in the middle of the state on the west gulf coast, we experience extreme growing conditions here in Tampa, Florida. Compared to Miami, 400 miles to our south, we are colder in the winter, and hotter in the summer. And lately, boy‑oh‑boy, are we hot in the summer! Summer is supposed to be our rainy season. In the "old" days, it would start to cloud up by 2pm, and be raining by 4pm. You could set your clock by it. The effect of that weather pattern was to keep the afternoon temperatures under 85°, and bring our nighttime temperatures into the 70's. But at the current time, we are in the grips of what is arguably the worst 5 year drought in the last hundred years. For the past 5 years, from May through August, we have had daytime temperatures at or near 90°F. coupled with nighttime temperatures that are above 80°F along with humidity between 75% and 90%. No clouding over near mid‑day, no cooling afternoon rains. In the last 5 years, I've lost a lot of begonias during this time. Those hot, over 80°F nights are begonia killers for sure! But last year, I built a new shadehouse. and spent the better part of early summer (see Convention, Denver) collecting new begonias to fill it with, and I was determined not to lose them, as I have in summers past.

Everything I know, everything I've read, and all the tips I've gotten on the subject of heat and begonias say that it is the nighttime temperatures that are the most crucial. So my goal was to try to lower those over 80°F nighttime temperatures in my growing areas.

My begonias grow in three distinctively different growing areas, and I did something different in each area. I will describe them each individually. In every case, a very light, porous potting mix is a must, or the plants smother and choke.

First, the outside shadehouse: Starting in May, I turned a fan on in there, and kept it running 24/7. Then, while at the garden center store one day, I noticed what they called a 'Personal Cooling System.' The same diameter as your standard garden hose, it's a hard, free‑standing form that looks just like a Cobra snake being charmed out of the basket. It stands about 2 feet high, and at the top are 2 fine mister heads. It was selling for $6. Attached to the garden hose, its intended use is to cool off a small area around a poolside, for example.

But I had other ideas.

After attaching it to my hose, I then raised it up 3 feet (1 put it up on a table), so that the mister heads were now about 5 feet from the floor. Then I strategically placed the fan behind it so that the mist was being blown through the shadehouse. At first, it took a little trial and error with the fan, but once I had the right distance and angle and speed, the results were even better than I expected. The mist covered an area about 6 feet wide, 12‑15 feet long and 8 feet high‑approximately 80% of my shadehouse. Even the hanging plants were misted.

The fan encourages evaporation, and as the water evaporates, it has a cooling effect on all surfaces ‑ the floor, the walls, the benches, the pots, the leaves and the air. So even when rain doesn't cool us down in the afternoon, my outside growing area is definitely cooler at night. The thermometer in there usually registers at least 5 degrees cooler than the outside air, which is often enough to bring the temperature in that area below 80°F. Hooray! And I think the plants like the mist, too, as it more resembles many natural begonia habitats.

As I already had the hose and fan, my entire investment in this system was the $6 I spent on that personal cooler / mister hose attachment. And since I did not come out in the mornings to find melted and mushy begonias, I feel like I got a very good return on that investment!

Next, I needed to do something in the room where I keep the terrariums. Each of 3 shelves has 1 or 2 four foot double fluorescent fixtures. The lights were on timers set for about 14 hours a day ‑ from 8am to 10pm. My house does have central air conditioning, but even with the ceiling fan running constantly, I was having trouble keeping the temperature in the terrarium room below 80°. And if the temperature in the room is 80°, inside the terrariums it had to be warmer.

So I decided to reverse the light timer. By that I mean that instead of having the lights on during the day, when the whole house is warmer anyway, I had them come on at night, when everything is cooler. And since it's also summer, when the days are long naturally, I set the lights accordingly ‑ on at 8pm, off at 10am. The terrarium room now stays below 80° at all times.

There is one downside to this plan, however, at least for me. Now that the lights are off during the day, I don't see as much as I used to, and the dusting of the containers and lights and grooming and watering etc. doesn't get done like it used to!

This method cost nothing to set up. It's hard to really compare electricity bills from last year, but the entire house is cooler, and it doesn't seem to me that the air conditioner has to work as hard. And I am much happier with the room staying below 80°.

The next growing area I needed to work on was the small greenhouse at the University of South Florida Botanical Garden that we refer to as the "Cool House." The glasshouse that houses most of the begonia species collection stays naturally cool due to oak tree shading and ventilation, but there are still some species that absolutely require (overall) cooler growing conditions, such as tuberous (which, by the way, will not grow in Florida at all), some of the thick stemmed species like B. wollnyi, those `picky' trailing scandents like B.solanthera, and some begonias that have been collected in the wild from cooler climates in Mexico, Peru and Ecuador.

Situated out in the full Florida blazing sun, this 10' X 10' fiberglass greenhouse can really cook! To keep the daytime temperatures as low as possible we use what (I recently learned) is commonly called a 'swamp cooler.' Fans at one end of the greenhouse exhaust air that is drawn through a drip pad at the opposite end. Daytime temperatures stay below 90°, without it they'd be over 120° in there. But again, my objective was to lower those nighttime temperatures.

We decided to install a portable room‑sized air conditioner to run at night. Given the limitations of the aluminum beams, we bought the largest (used) A/C we could find that would flit in the structure. I set the timer for the unit to turn on about 4pm and run all night long until about 8am. The drip pad continues to run, providing constant humidity, but the external exhaust fans are shut off so as not to draw the air conditioned air out of the greenhouse. They are set to come back on in the morning when the A/C cycles off. (An internal fan runs continuously.) I am extremely pleased with the results‑daytime temperatures are no higher than 90°, and nighttime temperatures are about 62°. This is very close to the natural habitats of many of our begonia species. I am even able to grow tuberous begonias such as B.evansiana in there, among others.

Obviously, this was the most expensive solution of the three I just described. The used air conditioner cost $175, and of course, the electricity it needs to run is not free. But the begonias are happy, I'm happy, and the small increase in the electricity bill is only temporary. When the weather breaks, usually in September or October, the air conditioner won't be needed again until next April or May.