Question: I was advised to cut down on fertilizer for my indoor plants in the winter because of a slower growth rate. I have not fertilized since early November. When should I begin fertilizing my indoor plants again? Do you recommend a particular indoor plant fertilizer?
Answer: Because of a slower growth rate, I usually reduce fertilizer for my indoor plants by about half during the winter months. You don’t indicate what kind of fertilizer you are using, but it sounds like you have completely stopped fertilizing.
Most soluble and liquid indoor plant fertilizers have rates for fertilizing every time you water plus a higher rate for monthly feeding. If you use the monthly rate, you can simply reduce the fertilizer to half the recommended rate during the winter. Since plants use less water as well as fertilizer during winter months, the “every time you water” rate probably doesn’t need to be reduced by much. In fact, I would tend to use the same rate. If I am using liquid or soluble fertilizers, I usually fertilize every time I water.
I prefer using slow release or timed release fertilizers for indoor plants. My favorite type of fertilizer is the coated type. The length of time between fertilizer applications is determined by the size of fertilizer pellet which is coated and the thickness of the coating. Coated fertilizers last between two and four months. Each time a plant is watered, some water molecules move through the coating and dissolve some fertilizer molecules. This fertilizer solution then passes back through the coating and enters the soil. The fertilizer is released according to watering frequency and tends to match growth rate fairly well. I mark my calendar as a reminder when it is time to fertilize again.
Plant leaf color and new leaf production rate are good indicators of fertilizer needs. If general leaf color fades to a lighter green, it is a signal that more fertilizer is needed. It is normal for a few older leaves to turn yellow before they drop. An increased number of older yellow leaves also indicates more fertilizer is needed. Brown leaf tips may indicate too much fertilizer is being applied. Some plants are sensitive to fluoride or boron in the water which may cause brown leaf tips.
A third type of indoor plant fertilizer is the tablet, stake or spike type. Tablets work similar to timed release types. A little fertilizer is dissolved off the outside of the tablet each time it is watered. Since the tablet is gradually reduced in size, it begins to release less fertilizer. So new tablets or spikes need to be added before the old ones are completely gone.
This is also a good time to groom indoor plants. Check them carefully and remove any brown or yellow leaves. Brown leaf tips may be snipped off with scissors. Instead of making a square cut, trim to retain the normal leaf shape. If mold is accumulating on top of the soil, you may be overwatering. Make sure the soil is dry on top before watering.
If dust has accumulated on shiny leaf plants they can be placed in the sink and sprayed with a kitchen spray nozzle. Fuzzy leaf plants can be damaged by applying water to the leaves. Leaf shine products are available which will shine as well as remove dirt. Leaf shine products can be toxic to certain plants. Test leaf shine products on a leaf or two for each type of plant before applying to the whole plant.