Answer: There are many reasons that the tips may be turning brown. The plant can be over-watered, under-watered, have too much heat, have too much fertilizer, or any combination of these factors and others. Then we throw into the mix all of the different varieties and its gets very confusing on why you get brown tips.
In the nursery these plants are watered and fertilized on a regular basis. They may be watered every day or every other day. All of a sudden the plant is shipped to a nursery or garden center and it isn't receiving the same treatment.
They may get less water and the fertilizers (salts) which are in the pot are getting higher because of the reduced moisture and can be burning the roots.
Speaking of under-watering, there are two ways (and probably more) to do this. The first is just not watering the plant enough and allowing the plant to wilt down before watering. A little droop may be OK, but not laying on the ground.
The second method is what I'll term "fake watering". We think we water but we really don't. This occurs when the soil has dried out, the soil may even be pulling away from the pot and the plant is re-watered. The water is going to take the path of least resistance and heads to the bottom of the pot. The soil may become moist in areas but the root ball or soil mass doesn't become sufficiently moist. It may be moist enough to let the plant perk up but the soil is still too dry. Again, this can be salts or the plant protecting itself by reducing the amount of foliage it needs to support. Result - Brown tips.
Over-watering can cause brown tips also. The root system is just not able to use all the water you provide. The roots may be swimming in water and rot off. Less roots means less leaves, and the plant will usually begin by losing the oldest leaves first.
Too much heat is another possibility. You may be asking yourself how can I have too much heat, it's 72 degrees in the house. That may be true but a plant sitting next to the window can be heating up more than you realize. We all have hot and cold spots indoors and out.
Once you've put on your detective cap, you'll be able to determine what is causing the browning tips on your peace lily.
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