Lime and Fluoride Sensitive Plants
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What does it mean if my plant is sensitive to lime and fluoride?
Most home water supplies have tap water that is hard, meaning it contains a high level of minerals and fluoride. Although the majority of plants are fine with being watered with tap water, some are more sensitive than others. Hard water isn’t always the best thing to water your plants with as it can be overly calcareous, meaning that it contains significant amounts of calcium carbonate (also known as chalk or lime). This can cause limescale deposits to develop - this is the same stuff as you might see building up in your home around taps and sinks etc. You may also notice that it causes spotty stains to appear on leaves after misting. Excessive buildup can interfere with your plant's ability to uptake nutrients.
Plants that are sensitive to lime and fluoride are sometimes also known as 'Ericaceous plants', meaning that they dislike alkaline soil (those that have a high pH). Some examples include azaleas, rhododendrons, heather and certain types of berries (like cranberries and blueberries).
Symptoms of lime sensitivity
Larger amounts of lime in the soil can cause a number of symptoms such as browning of the leaf tips, yellowing of the leaves, wilting and brown / black spots on the leaves. This is often particularly noticeable on tropical rainforest plants which have large patterned leaves, as they're susceptible to developing damage on the leaves as a consequence of lime.
If you've ruled out other possible causes for these symptoms and you think your plant may be sensitive to lime and / or fluoride, try switching up your watering method and make sure to only use filtered water if possible when watering your plants.
What to do about it
How hard the water is in your home depends on the area you live in - if you're unsure then you should be able to find information about the water hardness for your municipality online. If you find out that your area only gets hard water and you have a lot of sensitive plants then it may be worth investing in a water purifier so that you can water your plants using filtered water instead. Alternatively, you can use collected rainwater to water your plants.
Another filtration method is known as 'Reverse Osmosis'. This is the process by which pressure causes water to flow from a state of high concentration (where they are many contaminants in the water) through a semi-permeable membrane until it reaches a state of lower concentration (so there are now fewer contaminants present). The filtered water can then be used for your plants.
It's also important to flush the soil of mineral build-ups every now and then. Even if you typically use the bottom watering method to add moisture to your plants, you should change things up every now and then and water over the soil. This will help wash away any excess salts and minerals - just be sure to empty out any water that collects in the dish beneath your plant (it's also very important that your plant pot has drainage holes).