Gardening with Allen: 3 methods to fertilize indoor plants

My friend who has good success with indoor plants fertilizes her plants every time she waters them. Is that the best way to fertilize indoor plants?

There are at least three different methods of indoor plant fertilization that can be effective. Many indoor plant liquid and granular fertilizers have directions for fertilization every time you water. These are relatively low rates which provide a small amount of fertilizer every time. This system works quite well because plant growth rate and water use are proportional. When plants are growing rapidly, they use more water as well as fertilizer. When growth slows, they use less of both.

Most indoor plant fertilizers also have directions for a higher rate to be applied monthly. I prefer the every time system because I am less likely to forget.

A third system is to use a more highly concentrated fertilizer with longer intervals. High-analysis granules and concentrated plant food stakes and pills are two examples of this system.

My favorite fertilizer to use is slow-release coated capsules. Fertilizer pellets are coated with a porous plastic. Tiny holes in the coating allow water molecules to flow into the pellet, dissolve a small amount of fertilizer and flow out again. This provides a small amount of fertilizer to the root system every time they are watered just like the first system described. However, it is not necessary to add fertilizer to the water.

I use Osmocote brand slow-release coated fertilizer predominantly. I mark the calendar at three-month intervals to remind me when it is time to reapply. However, I also pay attention to plant appearance to tell me when extra fertilizer may be needed or when plants are getting too much fertilizer.

There are three main symptoms to look for. When more than an occasional older leaf turns yellow, it is a sign of nitrogen deficiency. This means that more fertilizer needs to be applied. If the newest leaves turn yellow with darker green veins, it is a sign of iron deficiency. All indoor plant fertilizers contain nitrogen but some do not contain iron. If you find iron deficiency, make sure you are using fertilizer which contains iron.

Fertilizers are salt compounds. When an excessive amount of salt accumulates in the soil, new leaves first start to turn light green to yellow without dark green veins. Brown leaf tips is another sign of too much salt. Too much salt can also come from salt accumulation from water softening systems. The best remedy for too much salt or over-fertilization is to apply a larger amount of plain water to dissolve the excess salt so that it drains out the bottom of the pot.

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