Fertilizer Program
🌿 Choosing the Right Fertilizer for Foliage Plants
Start with a base fertilizer that you can use for all your plants. While either slow-release granular or water-soluble fertilizers can be used, this guide focuses on water-soluble options.
For foliage plants, a fertilizer with an N-P-K ratio of 3-1-2 or 2-1-2 is typically recommended:
- 3-1-2: Promotes stronger nitrogen delivery — better for higher light environments with active growth.
- 2-1-2: Provides more balanced feeding — ideal for general use.
💡 Understanding Nitrogen Forms
Fertilizers often supply nitrogen in two common forms:
- Ammoniacal Nitrogen: Promotes lush growth and longer internodes. Can accumulate to toxic levels in low-light settings.
- Nitrate Nitrogen: Encourages compact, healthy growth and does not build up to toxic levels — making it the better choice for interiorscapes.
High-end fertilizers often contain a 50/50 blend of both forms, but for indoor plant health, prioritize those that provide mostly or entirely nitrate nitrogen.
✅ What to Look For
When selecting a fertilizer, base your choice on:
- The N-P-K Ratio: 3-1-2 or 2-1-2 for foliage plants
- The Nitrogen Form: Choose nitrate over ammoniacal nitrogen
Phosphorus and potassium sources are generally acceptable across most formulations and don’t require extensive review.
🌿 Essential Nutrients Beyond N-P-K
The next step in your fertilizer program is determining where all the other essential nutrients will come from. In addition to the primary macronutrients (Nitrogen, Phosphorous, and Potassium), plants also require a balanced supply of:
- Secondary Nutrients: Calcium (Ca), Magnesium (Mg), Sulfur (S)
- Micronutrients: Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), and Molybdenum (Mo)
Most quality fertilizers contain sufficient Sulfur, Manganese, Zinc, Copper, Boron, and Molybdenum. However, foliage plants often require additional Iron, Magnesium, and Calcium unless these are emphasized in your base fertilizer.
For palms, especially, extra Potassium and Magnesium will help maintain full, lush canopies with healthy older leaves.
🌱 Soil Matters
The type of soil your plants are grown in can drastically affect nutrient availability:
- Example: Palms grown in marl soil (common in South Florida) are already rich in Calcium — so extra Calcium isn’t needed, but Magnesium is.
- Excess Calcium can suppress Magnesium uptake, causing deficiencies.
- By contrast, plants grown in 100% soilless media will rely entirely on fertilizers for every single nutrient.
💧 Water Testing: A Smart Start
Don’t overlook your water source — it may contain useful nutrients or problematic elements. Testing your water helps you:
- Identify nutrients already being supplied through irrigation
- Detect contaminants that may interfere with plant health
- Prevent over-fertilization or nutrient imbalances
🛠️ Getting Started
You don’t need to be an expert to begin a good program. Just follow this simple plan:
- Step 1: Assume your soil contributes nothing — build your base program accordingly.
- Step 2: Get your water tested for nutrient content.
- Step 3: Use a complete fertilizer that supplies all required nutrients.
- Step 4: Refine your program over time based on observation, learning, and supplier feedback.
🌿 Fertilizer Rates & Frequency
Once you’ve chosen a fertilizer, the next big question is: how much and how often should you apply it?
In nursery environments with constant (daily) liquid feeding, a rate of 200–250 ppm Nitrogen (N) is typical for foliage plants. If you’re fertilizing less often — say weekly or biweekly — you can increase the ppm N to 300–400 ppm to compensate for the longer interval.
🧪 How to Adjust for Interiorscapes
For an interiorscape setting, feeding every other week with 50–200 ppm N is a good starting point. You can also try fertilizing:
- Every other watering
- Every third watering
- Or based on plant need and visual inspection
Remember:
- This is your base program. Plants in higher light or under stress may require more nutrients.
- Observe results over time and adjust accordingly.
🚫 Watch for Salt Buildup
At optimal rates, plants absorb what they need between applications, leaving no excess salts behind. However, high salt buildup can occur when too much is applied.
📊 Want to Get Precise? Use an EC Meter
For more scientific accuracy, test your soil’s EC (Electrical Conductivity):
- Remove a soil sample from the pot
- Add distilled water at a 2:1 ratio (e.g., 2 cups water for 1 cup soil)
- Stir and wait 20–60 minutes
- Use a calibrated EC meter to measure salt concentration
- Optional: Use a pH meter at the same time
Tip: If using tap water, measure its EC first and
As an example of the thought processes involved in designing a fertilizer program, consider the label of Scott's Champion brand water-soluble fertilizer 13-2-13:
This fertilizer has 12.1% of its 13% Nitrogen (N) as Nitrate Nitrogen, plus small amounts of all minor nutrients, plus larger amounts of additional Calcium (Ca) and Magnesium (Mg). All by itself, it satisfies the Nitrate Nitrogen requirement, the N-P-K ratio requirement, and the additional Calcium and Magnesium requirement.
However, this particular fertilizer lacks Sulfur (S). Sulfur is necessary, and a deficiency shows up as yellowing of newer growth with dark green veins. This condition can be corrected in a short time with the addition of a sulfur source. Therefore, one solution would be to not add additional sulfur and watch for a sulfur deficiency symptom, correcting it with one or a few applications of Ammonium Sulfate, Calcium Sulfate (gypsum), or Elemental Sulfur. Another solution would be to add a small amount of gypsum to the plants as they go out on the job. Both Calcium and Sulfur are beneficial, and gypsum can supply the Sulfur.
The only thing to add now is additional Iron (Fe). The iron in the 13-2-13 is only 0.05%. As a starting point, add additional Iron to bring the final concentration up to 0.5%, then monitor the plants for Iron deficiency symptoms. The Iron amount can be increased or decreased from this starting point depending on results.
With this program, all nutrients are supplied or there is a plan for addressing deficiencies if they occur. There are many choices of water-soluble fertilizers to use as a base and many products that will supply anything missing. Another idea could be to use a water-soluble 2-1-2 fertilizer without the extra Calcium and Magnesium, in conjunction with a liquid minor nutrient formulation that emphasizes Iron and Magnesium and enhances the minors package supplied by the base fertilizer.
A top dress of dolomite, as the plants go onto the job, would supply additional Calcium and Magnesium for 6 months to a year depending on the plant's environment. The main idea is to design a program that supplies all of the nutrients plants need — in the right forms (Nitrate Nitrogen), at the desired concentrations (additional Calcium, Iron, Magnesium, Potassium), and at the right frequency — so as not to cause problems.
Some important concepts to keep in mind:
13-2-13 means 13% Nitrogen (N), 2% Phosphorous (P), and 13% Potassium (K).
Using the value 75 in Example 1 – Section 1 below means you are working with a dry fertilizer, and the ounces (oz) are a weight measurement (16 oz = 1 pound). Use the value 78 in place of 75 if your starting fertilizer is a liquid. Then the ounces are fluid ounces (fl oz), and they are a volume measurement (128 fl oz = 1 gallon).
Parts Per Million or ppm can be stated as:
These are units for expressing a rate. This fact is hidden by the values 75 and 78 used in the calculations below. The value 75 represents 1 oz per 100 gallons expressed as milligrams per liter (mg/L), as shown below. For any dry material X, 1 oz of X mixed in 100 gallons of water results in a solution containing 75 ppm X.
Similarly, the value 78 represents 1 fluid oz per 100 gallons, expressed as 1 microliter per liter (µL/L). For any liquid material Y, 1 fl oz of Y mixed in 100 gallons of water results in a solution containing 78 ppm Y.
Example 1. Mixing fertilizers for a desired concentration
Let’s make the desired concentration 200 ppm Nitrogen (N) using Scott's Champion 13-2-13.
1. Use this formula to determine the ppm N achieved with 1 oz of this fertilizer in 100 gallons of water.
9.75 ppm N when 1 oz of 13-2-13 is dissolved in 100 gallons of water. You know that 75 is 75 ppm 13-2-13 when 1 oz is mixed in 100 gallons of water. Multiplying 75 by the percentage of Nitrogen in the 13-2-13 converts it to ppm Nitrogen when 1 oz is mixed in 100 gallons of water.
| Fertilizer | Answer |
|---|---|
| 20–10–20 | 15 ppm N when 1 oz is dissolved in 100 gallons |
| 15–5–15 | 11.25 ppm N when 1 oz is dissolved in 100 gallons |
| 24–8–14 | 18 ppm N when 1 oz is dissolved in 100 gallons |
2. Find the number of oz to dissolve in 100 gals of water to achieve 200 ppm N Desired ppm N / ppm N from 1 oz in 100 gals = multiplier to get desired ppm N in 100 gallons
Where X is the factor by which to increase the 1 oz / 100 gal rate to achieve 200 ppm N in 100 gallons of water
In this case:
The result tells us to multiply the 1 oz / 100 gal rate by 20.5 to achieve 200 ppm N in the 100 gallon solution.
Therefore, 20.5 oz of 13-2-13 dissolved in 100 gallons water will give you 100 gallons of a 200 ppm N mixture.
3. Find the number of oz per gallon to make the 200 ppm solution so that any quantity of fertilizer solution can be made
Just do the division:
Therefore, to make a 200 ppm Nitrogen (N) solution in 1 gallon of water, mix 0.205 oz of 13-2-13 in 1 gallon.
If you need 30 gallons of fertilizer, multiply the rate by 30 gallons:
So the result is: mix 6.15 oz of 13-2-13 in 30 gallons of water to make a 200 ppm Nitrogen (N) solution.
Here are all three steps again for this scenario using different values:
Using a water-soluble fertilizer with the label 12-4-12, make a 350 ppm N solution in 45 gallons of water.
1. ppm N of 1 oz in 100 gallons
2. Find the number of oz to dissolve in 100 gallons for a 350 ppm Nitrogen (N) solution
3. Find # of oz to dissolve in 45 gallons of water for a 350 ppm N solution
So, 17.5 oz 12-4-12 in 45 gallons of water will give you 350 ppm N solution. For clarity this can be stated another way: The number of oz of your desired fertilizer to mix into the quantity of water you will use to achieve the desired ppm is:
Where:
A = percent Nitrogen (N) in the fertilizer
B = desired ppm Nitrogen
C = quantity of water you want to make
X = ppm N when 1 oz of fertilizer is mixed in 100 gallons of water
Y = the factor by which to increase the 1 oz / 100 gal rate to achieve B ppm N
Example 2: Adding Additional Nutrients
1. From the discussion above, it was decided to add an additional source of Iron (Fe) to boost the 0.05% Iron delivered by the fertilizer. You can figure out the ppm Iron using the same technique that we used for Nitrogen, then increase the Iron — or any other element — with an additional fertilizer product.
Let’s assume that the chelated Iron product you will use is a dry product that contains 7% Iron, as specified on the label.
Here are the steps to figure out how much of this product to add to the fertilizer mixture to achieve the desired amount of Iron.
1. Find the ppm of Fe you are delivering with the base fertilizer (0.05%). Use the same method used above to find the ppm Nitrogen.
Mixing 1oz of 13-2-13 in 100 gallons the concentration of Fe is .0375 ppm. The rate you are going to apply this fertilizer at is 20.5 times this rate (See #2 in each of the scenarios above). So after mixing you will have a concentration of iron that is:
2. Using the same technique, find the ppm of the Fe you would be delivering if the base fertilizer contained your desired percentage of Fe (.5%)
3. Figure out the number of oz/100 gallons needed to make up the difference between 1 and 2 From the results of 1 and 2 the difference in the rates is
We need to add the right amount of additional iron to increase the concentration of iron, in the final fertilizer mix, by 6.912 ppm.
4. Find the number of oz of the 7% iron product to add to the fertilizer mix to get a 7.86 ppm Fe rate. This is the same problem as finding how much 13-2-13 to mix to achieve 200 ppm N.
Find the ppm of Iron (Fe) delivered in 1 oz per 100 gallons of water by the chelated Fe product.
Find the number of oz/100 gallons needed for the desired ppm Fe
So, 1.32 oz of the 7% iron product in 100 gallons will give you a rate of 6.912 ppm Fe. This, plus the iron delivered by the base fertilizer, will make the rate of iron 7.68 ppm, which is what we desired. Since the 1.32 oz is for making 100 gallons of mix we need to adjust this rate for the 30 gallons actually being made.
Finally, all quantities are known. To make 30 gallons of a 200 ppm Nitrogen (N) fertilizer solution with 0.5% Iron (Fe) using 13-2-13 and a 7% chelated iron product, you must mix 6.15 oz of 13-2-13 and about 0.4 oz of the 7% iron product in 30 gallons of water.
This may look complex because it is spelled out in great detail — hopefully for clarity — but the reality is that the math is not very involved. If you spend some time becoming familiar with ppm and these calculations, you will discover the simplicity.