Question
Hi, my name is Scott Koshowski and I  am from London, Ontario, Canada.  My question is in regards to Sodium concentration in water that will be detrimental to the health of grass.  At what level (parts per million) will you start to see negative effects visible in the grass quality?  Are there other factors that should also be taken into account such as the concentration of magnesium, calcium, etc.?  Is a sodium concentration of 300 - 400 ppm going to result in toxic effects to the grass?

Thanks for your help.

Answer
Normal sodium levels in drinking water are not lethal to plants. Sodium molecules are highly soluble and can be flushed through the root zone. Watering properly (e.g. deeply and infrequently as opposed to frequently and shallowly) will aid in this. Potassium molecules (required for plant growth) are also highly soluble and you should ensure that enough potassium are provided as sodium can replace potassium molecules in the soil causing grass to take up these instead. You can add twice yearly applications of sulfate of potash to the lawn if you need.

Sorry, but I don't know at which levels sodium affects grass.

The Calcium:Magnesium ratio concept is a bit controversial and in my estimation there has not been made convincing arguments to prove the theory. This ratio should not be used as a basis for fertilization or liming practices. Having sufficient levels of Ca and Mg is the proper method of evaluation, rather than trying to manipulate ratios. However, make sure soil pH does not increase too much with addition of calcium (target pH 6.2 - 6.8)