The Q&A Archives: Effect of Salt on Plant Growth

Question: My son (6th grade) is doing a science fair project. He is studying the affect of salt water on plant growth. He plans on growing the plants (marigolds or beans) from seed indoors using a seed starting kit with a plastic dome and seed starting mixture. Hewill have a control group watered just with tap water, and other groups watered with various concentrations of salt water. How often should he water, and would you know how much table salt he should use to make a mixture similar to sea water? <br><br><br><br><br>

Answer: Sea water has a salinity of around 34 parts per thousand. To make a solution, mix 34 grams of salt into a liter of water. Hopefully, his classroom has the equipment to help him make these measurements. <br><br>I'm curious why he would choose to waterhis plants with sea water? Is there a reason behind this? One way to tie this into a common occurance is to link it with plants' exposure to road salt, a common occurance here in the north.<br><br>As far a how often he should water, I would recommendthat he use the control plants as his indicator: when they need water, he should water them with a precise amount, then water the others (with varying concentrations of salt water) with the same amount. It's hard to give an amount/frequency of watering, since it will depend on the type and size of the plants, the size of the pots, room temperature, amount of light, etc. <br><br>I found an interesting web site with lots of information about sea water, just for some background information if that'shelpful. The address is<br>Or just search the net using the word "seawater". <br><br>He should also think about how he will measure plant growth. Height of the plants? Size of the leaves? Number of leaves? There are lots of ways of doing this, and it merits some consideration.<br><br>He might also consider spraying the leaves with saltwater solutions of varying concentrations, to mimic road salt spray. That way, he can water the plants with the same amount of pure water, and vary the spray. <br><br>Just a few thoughts. Hope it helps.

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