Sent by a customer, I haven't tried this, but I know others who have had sucess with this, and it's a lot "greener" than Vendex, my miticide of choice. I do not oppose or endorse this or any method. I do recommend trying out new techniques on one to a few plants first. Usually an expendible plant.....
"This is our favorite method for all hibiscus growing in small-medium pots and for houseplant hibiscus. You only have to do it ONCE to kill all spider mites and their eggs. It kills every kind of spider mite, even the most microscopic ones that can hide in cracks in the bark. This method does require precision and care. You'll need a timer and a thermometer - a kitchen "candy" thermometer is perfect. If the water is too hot or you leave the plants too long, you can damage the leaves and they will all fall off after treatment. If the water is much too hot and you leave the plants much too long, you could actually kill a very young plant. But if the water is too cool or if you don't leave the plants in the water long enough, you won't dissolve the covers of the eggs and kill the growing larvae, which means the infestation will come right back.
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Lay several hibiscus plants on their sides, pots and all, in a bathtub. You can put many of them close together in a single layer in the bottom of the tub.
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Fill the tub with water that is 110°F (43°C). Use a thermometer to monitor the temperature. Be careful not to go above 120°F (49°C) or you will cook your plants!
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Fill the tub until all the plants are covered, and weight the plants down to make sure all parts of all plants are submerged in the water. (An easy way to weight them is to cover the plants with two large towels, then to pull the two shelf racks out of your oven and lay those carefully over the top of the towels.)
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Set a timer for 10 minutes. (Don't count on your ability to watch a clock! If you leave the plants in too long, you may damage the leaves badly.)
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Drain out the water and stand the plants up in the tub until the excess water drains out of the pots.
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Scoop any soil in the tub back into the plant pots.
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Leave the plants out of bright light for a few hours to rest, then put them back where they belong. Be careful not to water until the soil dries out after this thorough soaking. "
