Large Alocasia has a burst of growth with the help of fertilizer. Large Alocasia has a burst of growth with the help of fertilizer.

Fertilizer 101

Big or small, all plants want to grow and fill our homes with lush, vibrant foliage. But growth takes time. Luckily, there is a secret weapon that can help them grow fast, look good, and even flower more frequently. That secret weapon, you might have guessed, is fertilizer.

As plants grow, they pull nutrients from the soil. Our homes are not exposed to the natural environmental processes many plants require to have nutrients in their soil replenished. Fertilizers will replenish those nutrients.

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Before we get into the make-up of fertilizers, here is some basic information on soil nutrients.

To complete their life cycle, plants need 17 essential nutrients, each in varying amounts. Three are found in air and water: carbon (C), hydrogen (H), and oxygen (O). Combined, C, H, and O account for about 94% of a plant’s weight.

The other 6% of a plant’s weight includes the remaining 14 nutrients, all of which must come from the soil. Horticulturalists call out 3 Primary Macronutrients: Nitrogen (N), Phosphorous (P), and Potassium (K). The plant needs these three the most out of all soil nutrients.

When you buy fertilizer or soil, you’ll usually see three numbers displayed. This is the NPK Ratio, the ratio of these three Primary Macronutrients.

The 3 Secondary Macronutrients are the following: Magnesium (Mg), Calcium (Ca), and Sulfur (S). These are the 3 nutrients after the main ones that get used most often.

The eight other elements—boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc—are called micronutrients because they are needed in much smaller amounts than the macronutrients.

 

The BIG 3:

Nitrogen (N)

What it does –

Nitrogen is a major component in the production of chlorophyll, which is used during photosynthesis to absorb sunlight. It is responsible for rapid foliage growth and green color.

When to use it –

When you see reduced growth, or after your plant has been in a pot without new soil for at least a year.

 

Phosphorous (P)

What it does –

Phosphorus promotes root formation and growth. It also benefits the quality of seed, fruit, and flower production, and increases disease resistance.

When to use it –

Use phosphorus when you want to help plants flower or fruit! It can also be used when you are seeing reduced growth, dark-green, purple or red color in older leaves, especially on the underside of the leaf along the veins, distorted leaf shape, thin stems, or limited root growth.

 

Potassium (K)

What it does –

Potassium helps plants overcome drought stress, improves winter hardiness, increases disease resistance, and improves the rigidity of stalks.

When to use it –

Bring in potassium when you see reduced growth, shortened internodes, necrotic (dead) spots on older leaves, and weak stalks.

 

Understanding the N-P-K Ratio:

Most fertilizers will have three numbers displayed on the package. These display the product’s Nitrogen, Phosphorus, and Potassium nutrients by weight. For example, if a 1 pound bag of fertilizer displays an N-P-K ratio of 4-4-6, that means it has .04 pounds of nitrate, .04 pounds of phosphate, and .06 pounds of potash (potassium). The rest of 0.86 pounds is a filler or bulking agent.

When someone mentions a balanced fertilizer, this means that all numbers of the N-P-K ratio are the same, so a 4-4-4 or 10-10-10, for example.

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Choosing a Fertilizer:

In general, fertilizers created for indoor plants have lower N-P-K ratios than fertilizers formulated for outdoor plants. This helps to prevent fertilizer burn on leaves and roots in indoor plants, which is a common result of introducing too many nutrients to the soil at once.

When choosing a fertilizer, seek out organic, natural fertilizers formulated for indoor plants. If you have fertilized before, seek out an N-P-K ratio that fits the needs of your plants. If you haven't fertilized before, choose a balanced fertilizer or a fertilizer on the gentler side (one where the N-P-K numbers are lower). This will give your plants a boost without running the risk of fertilizer burn. If they do well on a weak fertilizer, you can always increase to a stronger N-P-K ratio next season.

You can also dilute stronger fertilizers to ease plants into the growing season. Overall, it’s best to follow the instructions on a fertilizer package, then dilute to your own discretion.

Depending on the plant, you’ll want to avoid fertilizing in the winter. And instead of watering with fertilizer every time in the growing season, it’s typically best to fertilize every other watering.