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Tropical House Plant Care – Fertilizing House Plants

November 14th, 2009

Blooming Coleus between two Blooming Vincas

I forgot to pinch off the blooms on this coleus.

Your plants basically need two types of nourishment to survive: water and minerals. They get minerals by absorbing them from the damp soil through their roots. Outdoor plants can often gather all the minerals they need from their surroundings by themselves. However, houseplant care requires more careful attention from the gardener, since the nutrients available from the soil in a pot are limited.

What are those numbers on the bag of fertilizer?

Fertilizers contain the key elements needed: Nitrogen (N), Phosphorus (P), and Potassium (K) in varying proportions. The numbers given on a bag of fertilizer show the relative amounts of these three elements. For example, an 18-6-12 fertilizer contains 18% N, 6% P2O5, and 12% K2O. Other elements are also necessary, but in much lower amounts.

Two Different Coleus Plants

These really are both coleus. The short one had its blossoms pinched off, and the tall one has been grown indoors, so it hasn’t tried to bloom.

How do I decide what proportions to use for my plants?

The amount of each element needed will of course depend on the species of plant. Too much is just as bad for the plant as too little, so it requires a bit of research to learn exactly what is right for your particular tropical plant. Usually this help is available by either reading the label, or by asking your plant-supply person.

What is the function of each of the primary nutrients?

Without going too deeply into biochemistry, we can say that flowering tropical houseplants have a greater need for phosphorus, whereas leafy green house plants like a lot of nitrogen. Potassium helps fight plant diseases, and helps fruit-bearing plants by making it easier to transport other necessary elements through plant tissue.

Dying Coleus Plant

I brought this back in the house, and it began to wilt. It has to lean against the wall. I think it’s had it.

How can I tell if my plant is getting too little or too much fertilizer?

A nutrient deficiency will often cause the leaves to lose color, or to be smaller than normal. To help the plant recover, use a soluble fertilizer, so the nutrients can be absorbed faster. Too much fertilizer can result in brown leaf tips, or in wilting. This condition is easily relieved by soaking the whole pot in water to allow the excess nutrients to be washed away.

How and when do I apply fertilizer?

Personally, I prefer fertilizers that are dissolved in water, as this method is less likely to result in over-fertilization. I mix the fertilizer according to package directions, and then apply it by thoroughly watering the plant, until it flows out of the drainage holes in the bottom of the pot. I find that doing this about every two months is usually just about right.

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By being careful in fertilizing houseplants, you can make sure that they not only survive, but thrive. And be sure to take advantage of your plant-supplier. He should be happy to give you advice on how to keep your tropical houseplants healthy.

2 Responses

  1. gertrude sealy (1 comments) Says:

    where can i get a guava tree , i loss mine in january with a hard freeze in texas

  2. Professor (6 comments) Says:

    What a shame! I love guavas right off the tree. And they don’t take very long to bear fruit, either.
    Gurney’s has a guava plant for only $12.95. Just click their button in the left column, then enter “guava” into their search bar at the top of the page.

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Posted by Professor and filed under care, fertilizer, tropical house plants | 2 Comments »