Interiorscape Fertilization Program – A Step-by-Step Guide

Step 1: Choose the Right Base Fertilizer

Use either a slow-release granular or a water-soluble fertilizer. This guide focuses on water-soluble types.

Understanding NPK Ratios

Choose a 2-1-2 for low-light interiors or a 3-1-2 for high-light environments.

Forms of Nitrogen

• Nitrate Nitrogen (NO₃⁻): Promotes compact, healthy growth.
• Ammoniacal Nitrogen (NH₄⁺): Encourages fast, lush growth but may become toxic.

Step 2: Supply All Essential Nutrients

Plants require 13 essential nutrients:

• Macronutrients: N, P, K, Ca, Mg, S
• Micronutrients: Fe, Mn, Zn, Mo, Cu, B

Foliage plants and palms often need extra iron, magnesium, and calcium. Test your water to adjust nutrient delivery accurately.

Step 3: How Much and How Often to Fertilize

• Daily feeding (nursery): 200–250 ppm N
• Periodic feeding: 300–400 ppm N
• Interiorscapes: Feed every 2nd or 3rd watering or every 2 weeks at 50–200 ppm N

Avoiding Salt Build-up

Look out for wilted plants despite moist soil. Test salts using an EC meter:

1. Mix 1 part soil with 2 parts distilled water
2. Stir and wait 20–60 minutes
3. Measure EC (mS/cm)

EC Interpretation Table

EC Value	Nutrient Level	Recommendation
0.2 – 0.5	Very Low	Add fertilizer
0.5 – 0.8	Low	Slightly increase feeding
0.8 – 1.2	Optimal	Maintain current program
1.2 – 1.8	Moderately High	Monitor and reduce slightly
> 1.8	High – Possible Toxicity	Flush media and reduce feed

Understanding Fertilizer Calculations

General rules:

• Dry fertilizer: 1 oz in 100 gal = 75 ppm
• Liquid fertilizer: 1 fl oz in 100 gal = 78 ppm

PPM Calculation Formula Chart

Type	Formula	Description
Dry	PPM = 75 × (% nutrient)	1 oz per 100 gallons
Liquid	PPM = 78 × (% nutrient)	1 fl oz per 100 gallons

Example: 13-2-13 Fertilizer (13% N)

1 oz in 100 gal:

75 × 0.13 = 9.75 ppm N

To make a 200 ppm N solution:

• 200 / 9.75 = 20.51 oz per 100 gal
• 20.51 / 100 = 0.205 oz per gallon
• 0.205 × 30 = 6.15 oz for 30 gallons

Adding Extra Iron (Fe)

To supplement from 0.05% to 0.5% iron using 7% chelated iron:

• Base Fe delivery: 75 × 0.0005 × 20.5 = 0.768 ppm
• Target Fe: 7.68 ppm → Difference = 6.912 ppm
• Iron product: 75 × 0.07 = 5.25 ppm per oz
• Needed: 6.912 / 5.25 = 1.32 oz per 100 gal
• For 30 gal: 1.32 × 0.3 = 0.396 oz

Final Formula Example

• 200 ppm N: 6.15 oz of 13-2-13
• 0.5% Iron (7.68 ppm): 0.4 oz of 7% chelated iron

Key Concepts

• 13-2-13: 13% N, 2% P, 13% K
• Formulas:
• PPM (Dry) = 75 × % nutrient
• PPM (Liquid) = 78 × % nutrient

Practice these formulas and adjust your program as your plants grow. You’ll gain confidence and success with every application!