Soilless Grow Mix Porosity
Delivering the correct porosity in soilless grow mixes is essential for maintaining healthy indoor plants. The balance between air pockets and moisture retention ensures roots get the oxygen they need while avoiding overwatering conditions that can lead to root rot, stunted growth, and disease. Too little porosity results in waterlogged roots, while too much causes rapid drying and stress for your plants. Whether you’re using traditional materials like peat and pumice or exploring innovative options like raw hemp fibre, finding the right mix can make all the difference. Our Porosity Calculator evaluates 11 substrate additives, giving you the insights needed to create the optimal mix for your plant’s needs, promoting healthier growth and a robust root system.
When crafting a soilless grow mix, achieving the right balance between air-filled porosity (AFP) and water-holding capacity (WHC) is crucial for root health. Here’s a general guideline for optimal porosity:
Air-Filled Porosity (AFP): 15-30%
- This refers to the portion of the mix that remains filled with air after watering.
- Too little air (<10%) leads to oxygen deprivation and root rot.
- Too much air (>35%) causes rapid drying, making it hard for roots to absorb nutrients.
Water-Holding Capacity (WHC): 30-60%
- This percentage represents the amount of water the substrate can retain after draining.
- Too low (<30%) causes frequent watering and nutrient loss.
- Too high (>60%) risks waterlogging, suffocating roots.
Balanced Example for Many Plants:
- AFP: 20-25%
- WHC: 45-50%
This range ensures a stable environment with enough moisture to sustain the plant while keeping roots oxygenated, reducing the risk of diseases like root rot.
These ratios vary depending on the plant’s needs. For example:
- Succulents: Lean towards higher AFP (25-30%) and lower WHC (30-40%).
- Tropical plants: Prefer moderate AFP (15-20%) with higher WHC (50-60%).
Soil Properties
Understanding Soil Properties
Interpretation of Color Codes:
- Red: Dangerous conditions for plants in selected media
- Orange: Suboptimal conditionsfor plants in selected media
- Chartreuse: Acceptable conditions for plants in selected media
- Green: Optimal conditions for plants in selected media
Property Descriptions:
Average Particle Size: Represents the average size of soil particles. Smaller particles (lower values) create denser soil with smaller pores, while larger particles create looser soil with larger pores.
Total Porosity: The percentage of soil volume that is not occupied by solid particles. Higher porosity means more space for air and water.
Water Retention: The soil's ability to hold water against gravity. Higher values indicate soil that retains more water, which can be beneficial for moisture-loving plants but may lead to poor drainage.
Air-filled Porosity: The percentage of soil volume filled with air when the soil is at field capacity (after excess water has drained). This is crucial for root respiration and overall plant health.
pH: A measure of soil acidity or alkalinity. A pH of 7 is neutral, below 7 is acidic, and above 7 is alkaline. Most plants prefer a slightly acidic to neutral pH (6.0 to 7.0).
CEC (Cation Exchange Capacity): A measure of the soil's ability to hold and exchange nutrients. Higher CEC values indicate better nutrient retention. Measured in milliequivalents per 100 grams of soil (meq/100g).
New Materials:
Horticultural Charcoal: Improves soil drainage and aeration while also absorbing excess moisture and nutrients.
Pumice: A lightweight, porous volcanic rock that improves drainage and aeration in soil mixes.
LECA (Lightweight Expanded Clay Aggregate): Clay pellets that provide excellent drainage and aeration, often used in hydroponics.
PON (Plant Optimal Nutrient): A soil-less growing medium that provides excellent aeration and water retention.
Hemp Fiber: A renewable resource that improves soil structure, water retention, and aeration.
