KEEPING FUCHSIAS ALIVE IN
VERY HOT WEATHER
By Kevin Handreck
Kevin Handreck is an acknowledged Australian soil scientist.
By Kevin Handreck
Kevin Handreck is an acknowledged Australian soil scientist.
When fuchsias are dying and the weather is hot, there are two possible contributing causes to this problem.
One is that the fuchsias were simply killed by high temperatures around their roots. Growing fuchsias in plastic pots during summer is a near-certain method of killing them. I would say that for much of Australia, plastic hanging pots are virtually 100% lethal in summer. Fuchsias evolved mainly in high mountain areas of Central America, at elevations of 2000 to 3000 meters. Their roots would never have to cope with temperatures over about 25°C. Growing medium temperatures above about 30°C are lethal to their roots.
No amount of fungicide will prevent death by high temperatures. The only cure is prevention, by keeping the roots cool either by growing them in containers that have their own built-in evaporative cooling in the way of a porous outer covering to the potting mix. The only hanging containers to use for fuchsias are baskets that have coconut fiber or synthetic cloth liners, without any inner liner of plastic sheeting.
The other possible cause of death is that their roots were killed by pathogens that were stimulated to attack because the roots had already been injured through lack of oxygen. This lack of oxygen probably came about through a combination of a potting mix that was too fine and too frequent irrigation.
Plant roots need water, of course, but they also must have oxygen circulating around them if they are to remain healthy. That means that some of the spaces (pores) in the potting mix must be large enough to contain air when drainage has stopped after irrigation. For fuchsias, something like 15 to 20% of the total volume of the mix must be air space just after drainage has finished. If the percentage of air space (air-filled porosity) is, say, only 8-10% AND irrigation water is applied so frequently that the mix remains constantly wet, movement of oxygen from the atmosphere to the roots is too slow for good root health. The stressed condition in them causes them to secrete chemicals. These are readily interpreted by pathogens such as Phytophthora cinnamomi, Fusarium and Pythium species as,“ Come and get me; I am good to eat” The main way of preventing this ’over-watering’ syndrome is to use an open, free-draining potting mix. You need a potting mix that has an air-filled porosity of at least 15% if you live in an area with hot summers and at least 29% if you live in a generally cool area. Some potting mix bags give the air-filled porosity range into which the mix falls. For others, you will have to check the mix yourself. Do not use mixes that contain sawdust or greenwaste compost. The rapid decomposition of these components leads to rapid reduction in air-filled porosity. As with death by heat-stroke, death by drowning is not prevented by applications of fungicides. All they will do is cause a lingering death rather than a rapid one. The cause has to be eliminated.
Article from the B.C. Fuchsia & Begonia Society Eardrop, September 2004.
Edited to fit available space.