There is much confusion about using fertilizer (plant food) for indoor potted plants. Houseplants use nutrients in minute quantities and only when they are in good light, and are healthy and growing vigorously. Fertilizer is NOT medicine and should not be used on ailing plants.
Much ado is made about using organic or commercial fertilizers. Use whichever you prefer, but don't expect "miracles" from its use and don't expect it to solve your plant problems. It is tempting to "fix" plant problems with the simple application of fertilizer, but it is a rare problem that is resolved by fertilizer.
It is easy to find photos of plants that exhibit symptoms of nutrient deficiencies along with the specific nutrient that is lacking. Unfortunately, it is rarely mentioned that the first step in correcting a nutrient deficiency is checking the soil pH. Most tropical plants require a soil pH in the 6.0 to 6.8 range (mildly acidic). A pH outside that range will bind up the nutrients and make them insoluble or unavailable for the roots to absorb. So the problem may not be lack of certain nutrients in the soil, but a pH problem that is preventing them from being absorbed. If you suspect a nutrient deficiency, always check the soil pH first. If you correct the pH problem, then the nutrients already in the soil will become available to the plant.
Plants grown in nurseries are in soil with proper pH levels. However, if you repot and use soil outside the proper pH range, that may create a problem. The use of compost and other organic materials in your indoor potting mix may substantially alter the soil pH. Another cause of improper pH in soil is using hard water to irrigate your plants. If the quality of your soil is good and your water is not hard, then soil pH is not likely to be a problem.
The label dilution rates on fertilizer labels are based on ideal nursery environments, which few of us have in our homes. If you feel compelled to use fertilizer, use it at half the dilution rate and no more than once per month in most instances. Over fertilizing, which can cause burning of tender roots, is a more common problem than nutrient deficiency. So err on the side of less rather than more.
