Should I Flush My Hemp Field?

October 15, 2020
Category: Growing Tips

To flush, or not to flush, that is the question. While the marijuana industry has established practices regarding flushing, flushing in CBD and industrial hemp production is still experimental. Grower’s varied perspectives may make the the question of “Should I flush my hemp field?” a confusing decision. In this article we’ll explain:

  • What flushing is in industrial hemp (Hint: It isn’t related to toilets.)
  • The arguments for and against flushing
  • Flushing methods for various cannabis growing mediums

What is Flushing In Industrial Hemp?

The process of flushing hemp fields is fairly simple. For a short time before harvest, you stop feeding the plants nutrients and run pure water or a flushing agent through the soil to remove nutrients from the root area. This allows the plants to break down the nutrients they’ve already absorbed and use them up. While the process is simple, choosing whether to implement it is more complicated. 

Does Flushing CBD Crops Matter?

CBD from industrial hemp has been ruled legal, but the jury’s still out on whether flushing is a necessary step in industrial hemp production. 


  • Costs more in production time
  • May improve flavor
  • May improve burnability
  • Adds a step to the growing process
  • Deprives the plants of nutrients for a short period of time

That final point is the main question of debate: does depriving the plants of new nutrients for the final week or two of growth create a meaningful benefit? 

Some growers say “yes,” while others argue that flushing may offer no benefit. Proponents of flushing attribute improved flavor to the process, which allows the plants to use up excess nutrients as well as get rid of salts and contaminants. Those who argue against flushing point to studies that show no significant difference between the mineral and nutrient content of flushed and unflushed plants, as well as blind taste tests in which consumers preferred unflushed Cannabis flower.

Whether you choose to flush your industrial hemp fields may depend on the end-use of your product. 

If flavor and burnability matter, you may have more reason to flush, while if you’re growing cannabis primarily for CBD content or other industrial hemp applications, flushing may provide no benefit. There is little evidence that flushing increases CBD content or plant health. Flushing does tend to push nutrients into the flower, forcing buds to swell; this may improve the flavor of the dried CBD flower. 

Whether or not you flush may also affect how the plant matures in its final weeks and the concentration of terpenes in the plant’s profile. Suppose you are growing primarily for essential oil extraction. In that case, you may choose not to flush to keep your plants increasing growth in that final week or two before harvest, as terpenes become more concentrated as the flower matures.

In this adventurous line of work, careful experimentation is the key to learning what works best. Testing the effects of flushing on your specific crops will yield the most accurate information to help your crops, your business, and the hemp industry flourish. You might try growing two sets of crops under all the same parameters but flushing one while leaving the other unflushed. See what happens and share your findings with the industrial hemp growing community. 

How to Flush Your Hemp Field

If you choose to flush your hemp, the specifics of the process will differ depending on your growing medium. You can flush with plain water or with a flushing agent. A flushing agent will chemically bond with nutrients to help them exit as the chemically enhanced water passes through the growing medium. 


In soil, flush the roots with plain water or a flushing agent for two weeks before harvest. Heavier clay soils may require a slightly longer flush of 15-20 days, while looser sandy soils may require a slightly shorter flush of 7-10 days. Use water with a pH of 6.0-6.8. If you are growing cannabis in organic soil that you’ve amended specifically for its nutrient specifications, you may not need to flush. Flushing would damage the soil ecosystem you’ve built. 

Rockwool or Coco

If you’re flushing plants grown in Rockwool or Coco, use water with a pH of 6.0-6.8 for one week. 


In medium-free hydroponic systems, flush with water at a pH of 5.5-6.5 for 3-4 days. This will replace the nutrient-rich water, giving the plant a chance to use up the nutrients it has already absorbed. In medium-based hydroponic systems, flush with water at a pH of 5.5-6.5 for 4-7 days. 

Want to start growing hemp? You can purchase several varieties of hemp clones here. Learn more about growing Cannabis for CBD production on our blog: we cover rooting, testing, terpene profiles, growing schedules, regulations, and more.