As a cannabis cultivator, you know temperature and humidity are critical environmental factors in your grow room. But did you know it’s the relationship between temperature and humidity, known as VPD (vapor pressure deficit), that truly determines plant growth and health?
By mastering VPD, you can optimize your entire cannabis cultivation operation for faster growth, bigger yields, and more potent buds.
What is VPD?
VPD measures the difference between the amount of moisture in the air and how much moisture the air can hold at a given temperature.
Warm air can hold more moisture than cool air. So if warm air contains 60% relative humidity, it has a higher VPD than cool air at 60% RH.
Why VPD Matters
Transpiration! Plants absorb water through small openings on their leaves called stomata. Higher VPD causes the stomata to open wider as moisture evaporates faster. This allows more rapid transpiration and CO2 absorption for growth.
At lower VPD, the stomata close to prevent excess water loss. This slows transpiration, photosynthesis, and ultimately cannabis development.
Each cannabis growth stage has an ideal VPD range for optimized growth and yield:
- Seedling: 0.5 to 0.8 kPa
- Vegetative: 0.8 to 1.0 kPa
- Flower: 1.0 to 1.35 kPa
Monitor VPD with sensors and use temperature and humidity controls to maintain the proper ranges. Higher daytime VPD with lower night VPD is optimal.
Here’s a handy VPD chart from Dr. Greenhouse for reference.
Dialing in VPD results in faster nutrient absorption, bigger leaves, sturdier stems, more bud sites, and bigger flower clusters.
Plants grow more vigorously, producing higher yields in shorter grow cycles. Terpene and cannabinoid production increase as well.
Understanding and controlling VPD is a must for your environment. Master it and get ready for your highest quality, highest efficiency cannabis grow yet.