Humidity and Plants

Frequently asked Questions:

Q: Why is humidity so important to plants?

A: Plants do not have a heart or a bloodstream like we do. What a plant does is absorb water and nutrients through the root hairs and evaporates water only out the leaves, leaving the nutrients behind. This method of moving the nutrient inside the plant's own system is called "transpiration". In high humidity, it becomes more difficult for the plant to evaporate the moisture it needs to for transpiration. This can result in nutrient deficiencies and color changes on the leaves.

Q: What is the best relative humidity?

A: Most books say 50% . We do not know where the research for this number comes from, but virtually everyone sticks to this number. We suspect, however, that this research comes exclusively from plants grown in soil. From experience, we know that the best relative humidity depends on a number of factors and that for experienced hydroponic growers, in urban gardens, with their plants growing very quickly, lower humidities than 50% have proven to help with speed. In soil, though, it is best to stick to the range around 50%.

Q: In Hydroponics, how low can you make the humidity and still speed up growth to the maximum?

A: You know, there is a graduate student at a large Agricultural University somewhere in the Midwest or maybe in Cali. He's haunting the college, drinking too much beer, racking his brain for a topic on which to base his dissertation. You can see him hanging out at the local coffee shop with his yellow pad, frustrated, furiously scribbling anything for show. If he had not alienated all his friends by being so self-absorbed, one of them would have directed him to this website by now--and then we could all know the answer.

Q: Uh,..OK...........What other new research is going on?

A: The new research is on "water vapor pressure deficit" An easy way to get a handle on this one is to look at the current temperature and to compare it to the dewpoint. A high VPD is dry, while a low VPD is wet.