Chlorine and water have an important relationship, and not just in swimming pools. In plants, chlorine helps regulate water. To get technical, the ionic form of chlorine (chloride) provides a counter balance to potassium ions in the opening and closing of stomata, regulating how much water the plant takes in. This makes chlorine especially important in drought conditions or when water is less available. Chlorine also breaks the bonds that hold water molecules together during photosynthesis, helping to move the photosynthesis process along.
As one of the water-soluble micronutrients, chlorine is very mobile in both the soil and the plant. Plants take in chloride, the anion form of chlorine, along with water through their roots. It also helps transport other essential nutrients such as calcium, magnesium and potassium. Chlorine is usually found in ample quantities in the salts found in garden soil, and its uptake by plants is relatively unaffected by soil pH.
The symptoms of chlorine deficiency will show up in new tissue first. It can cause wilting or browning of leaf tips and a stubby root system. As with everything, though, too much of a good thing is also bad – an overabundance of chlorine can cause a plant to form thicker, smaller leaves or cause older leaves to yellow along the edges. So, unless your soil test tells you otherwise, save the chlorine for your swimming pool, not your garden.