The Q&A Archives: Mass Mortality Of Wave Petunias

Question: Anybody know what causes sudden mass mortality of Wave petunias ? For the last 4 years, I would plant out around 30
hanging baskets of purple wave and Misty lilac Wave petunias
in March; I make my own soil, mostly from coir, perlite,
vermiculite, water-holding polymers. All the petunia baskets would grow wonderfully till the temperature hits 90 degrees and more, and then they would suddenly all die within a week !! Water is not a problem; my hanging baskets
are the self-watering kind that have a big reservoir on the bottom, with a hole just above the water line. When the temperature goes above 90 degrees, the plant would suddenly
start getting wilty and the next day the whole plant would be dead !!

Answer: How disappointing to have your petunias become victims of the heat! In general, most tender annuals and some perennials react to high temperatures (90F and above) by slowing down and sometimes even stopping their respiration and transpiration in an effort to conserve moisture. This results in wilting and can eventually cause cell collapse in both stems and leaves. It's not a lack of water that's causing the wilting but the inability of the water around the roots to be transported up through the plant's vascular system because the stomata (natural openings in the leaves) have shut down in a defense against the heat. Usually heat stressed plants resume transpiration and respiration when the temperatures drop below 90F, and by the next morning they're fully recovered. Apparently your petunias are becoming so over-heated that they can't recover even when the temperature drops. If the baskets are hanging out in the afternoon sunshine, the roots may be baking, as well. Have you tried hanging the baskets where they receive only morning sun? This may give them just the protection they need to endure and then recover from high temperature stress.

Hope you have better success with your petunias in the future!

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