1. What is Vapor Pressure Deficit?

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 growers as it affects plant transpiration and growth.

2. How Does the Calculator Work?

The calculator uses the VPD equation:

Where:

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

Explanation: The equation calculates the difference between the actual water vapor pressure and the saturation water vapor pressure at a particular temperature.

3. Importance of VPD for Cannabis Plants

Details: Proper VPD levels ensure optimal transpiration rates, nutrient uptake, and plant growth. Cannabis plants thrive when VPD is maintained between 0.8-1.2 kPa during the day in vegetative stage and 1.0-1.5 kPa during flowering.

4. Using the Calculator

Tips: Enter SVP in kPa (which depends on leaf temperature) and RH in percentage (0-100%). Both values must be valid (SVP > 0, RH between 0-100).

5. Frequently Asked Questions (FAQ)

Q1: Why is VPD important for cannabis cultivation?
A: VPD directly affects stomatal opening, transpiration rates, and nutrient uptake - all critical for healthy cannabis growth and maximum yields.

Q2: What are ideal VPD ranges for cannabis?
A: Vegetative stage: 0.8-1.2 kPa; Flowering stage: 1.0-1.5 kPa; Nighttime: 0.4-0.8 kPa. These ranges may vary slightly by strain.

Q3: How do I measure SVP?
A: SVP can be calculated from leaf temperature using the Arden Buck equation or obtained from psychrometric charts.

Q4: What happens if VPD is too high or too low?
A: Too high: plants close stomata, reducing growth. Too low: poor transpiration, risk of mold/mildew from excess humidity.

Q5: Can I use this for other plants?
A: Yes, but ideal VPD ranges vary by plant species. Cannabis prefers slightly higher VPD than many other plants.