If you love plants, and have a Koi pond, chances are you have some plants in your pond. The problem is always how to avoid bringing in pathogens and parasites with the new plants.  Salt baths used to be used to remove pathogens on incoming pond plants, although Potassium Permanganate at a 20ppm dose for 30 minutes is now considered much more effective.  For sensitive plants, try 10 ppm for 3-6 hours. Always bare root the plant before dipping in PP, and then replant in sterilized soil before placing in the pond.  Watch the plant carefully for wilting during the treatment.  If the treatment is hurting the plant, then dilute the PP and use a longer treatment.  K.O.I. recommends using salt only in Quarantine and holding tanks to aid sick or stressed fish.  While salt used to be a common treatment for parasites, the overuse of salt has caused most parasites to become resistant to salt. 

If you are wondering about the how much salt certain plants can tolerate, I have copied the following information from http://www.bonniesplants.com/.

The plant versus salt test was run over a period of 6 weeks. The test was run TWO separate times to ensure validity. Healthy, actively growing plants were set in a 600-gallon stock tank. Aeration was added to make sure that the salt was evenly distributed throughout the tank. Salt was measured once a week using a refractometer and LaMotte salinity test kit. Each plant was physically removed from the tank and inspected before the next level of salt was added. Water was replaced as need because of evaporation and the salt level then adjusted for that period. Every 2 weeks more salt was added to bring the level up another 0.1%.

The letter "D" in each box represents the level of salt at which the plant died. I increased the salt by 2-week periods because it is generally recommended that pond salt be used for no more than 3 weeks in the case of parasites. What I was looking for is what plants that can tolerate 0.3% salt for a period of 2 weeks or more. I have also included notes for specific plants.