Balancing Moisture Levels for Healthier Plants and Increased Productivity

Both over and under watering are common mistakes that stress plants, leading to significant inefficiencies in biomass production. Cultivators can help prevent this problem with a better understanding of dry back. 

After plants are watered, the medium has to be able to dry back to a state where plants become most efficient at drinking water again. Roots are unable to uptake nutrients without water and should not be deprived for too long. The goal is to get the plant to a state where it is ready to begin taking up nutrients again without inducing negative stress.

Drying back too much is comparable to under watering. Not drying back enough is considered overwatering.

Dry back can be looked at similarly to human digestion. Dry back is like either waiting until you are starving to eat or eating a full meal when you are stuffed. Both are inefficient and lead to stress on the body. Finding the happy medium is key!

What are factors that affect dry back?

  1. Water Holding Capacity of Medium: Perlite and long strand coco fiber have a low water holding capacity. Clay, short/fine strand coco fiber and peat moss all have a high water holding capacity.
  2. Size of Plant: Larger plants tend to consume more water.
  3. Lighting: Higher PAR intensity usually means faster drink rate.
  4. Humidity & Heat: Affects plant transpiration rate.
  5. Size of Container: Too big of a container can exacerbate overwatering.  

How do you know when to water a plant? There are different ways to understand if dry back has occurred. Some cultivators will use moisture sensors to measure medium water content. This is especially true in large scale cultivations vs. smaller home grows. If you don’t have a moisture sensor you can feel the soil or the weight of the pot. If the medium cannot give up water when compressed, the roots will not be able to draw water from it either. It’s time to hydrate. 

Does the plant have enough water to make it to the next watering event? If the answer is yes, do not water it. If the answer is no, provide water. A lot of this has to do with the plant’s ability to maintain turgor pressure. 

Effects of Over Watering: Roots want oxygen. Oxygen can become depleted if too much water is present in soil for too long of a time. This can cause unwanted pathogens to grow, increasing risk of root rot. Roots cannot sustain optimal health by sitting in deoxygenated water.

Effects of Under Watering: Ultimately, under watering starves the plant. If the roots go too long without water, nutrients in the medium will not get taken up by the roots and utilized by the plant.

Optimal dry back levels are dependent on medium, i.e. rockwool vs soil. While optimal dry back for rockwool is 40-60%, it may be 30-50% for some soil substrates. Other significant variables include strain, metabolism and environment.

As a cultivator, you always have to adjust to changing variables to achieve the optimized best practice. Understanding dry back comes with time and experience!

Understanding the Foundations for Healthy Plant Development