1. What is Vapor Pressure Deficit (VPD)?

Vapor Pressure Deficit (VPD) is the difference between the amount of moisture in the air and how much moisture the air can hold when it's saturated. It's a crucial measurement for cannabis cultivation as it affects plant transpiration and nutrient uptake.

2. How Does the Calculator Work?

The calculator uses the VPD equation:

Where:

• \( SVP \) — Saturation vapor pressure (kPa)
• \( RH \) — Relative humidity (%)

Explanation: VPD represents the "drying power" of the air, calculated by comparing how much water vapor is in the air versus how much it could potentially hold.

3. Importance of VPD for Cannabis Growth

Details: Proper VPD levels ensure optimal transpiration rates, nutrient uptake, and stomatal function. Ideal VPD ranges vary with growth stage (0.8-1.2 kPa for veg, 1.0-1.5 kPa for flower).

4. Using the Calculator

Tips: Enter SVP in kPa (calculated from leaf temperature) and RH as a percentage. Both values must be valid (SVP > 0, RH between 0-100).

5. Frequently Asked Questions (FAQ)

Q1: Why is VPD important for cannabis?
A: VPD directly affects transpiration rates, nutrient uptake, and overall plant health. Proper VPD prevents issues like nutrient deficiencies or mold.

Q2: What are ideal VPD ranges for cannabis?
A: Generally 0.8-1.2 kPa for vegetative growth and 1.0-1.5 kPa for flowering, though optimal ranges vary slightly by cultivar.

Q3: How do I measure SVP?
A: SVP is calculated from leaf temperature using the Arden Buck equation or similar formulas based on temperature.

Q4: What happens if VPD is too high or low?
A: Low VPD slows transpiration (risk of edema), while high VPD causes excessive transpiration (risk of nutrient burn).

Q5: Does VPD affect CO2 uptake?
A: Yes, proper VPD ensures stomata remain open for optimal CO2 absorption while preventing excessive water loss.