How and When to Flush Cannabis Plants

Flushing cannabis plants involves running pH-balanced water through the growing medium to remove the build-up of unwanted residual salts, generally occurring during the final two weeks of flowering. In this article, we will provide a thorough four-step guide on flushing cannabis plants and compare two fascinating studies by Rx Green Technologies and the University of Guelph on flushing flushing vs not flushing chemical analysis of cannabis

What is Flushing?

Just as we cleanse our bodies to remove toxins and promote well-being, some cannabis growers flush their plants with water to eliminate residual nutrients that have accumulated in the growing medium or root zone. This essential process ensures healthier plants and enhances the final product’s flavor and quality. The result is a smoother, more enjoyable experience for cannabis enthusiasts.

Is it Ok to Flush During Flower?

Flushing is typically performed during the later part of the flowering stage when nutrient accumulation occurs most significantly. Growers implement heavy feeding schedules to enhance bud development, which can result in excess salts and unabsorbed nutrients in the growing medium. 

Flushing removes these build-ups, ensuring the buds remain clean and flavorful. Make sure to only flush cannabis plants before harvest to prevent detrimental effects.

When to Flush Cannabis Plants

So, when’s the best time to flush cannabis plants? Flushing weed during the vegetative phase can impede growth, as plants need consistent nutrients to develop strong roots, stems, and foliage. Performing a flush at this stage may lead to nutrient deficiencies, ultimately slowing growth and delaying the plant’s transition to flowering. 

The only reason to flush during vegetative growth is when there is excess nutrient build-up, which can cause nutrient imbalances. Flushing can fix this, and a normal feeding program can be resumed.

Between Growth Phrases

While nutrient accumulation during the vegetative stage has little effect on the overall quality of the resulting flowers, some growers advocate for flushing cannabis plants between the vegetative and flowering periods. This flushing period is believed to help reset the plants by eliminating excess nutrients, allowing them to redirect their energy and resources toward producing robust, high-quality flowers once plants reach the flowering stage.

Pre-Harvest

Flushing cannabis plants during the final two days of the flowering cycle is recommended, as it mitigates chlorophyll production that can adversely affect taste and aroma. This process forces the plant to rely on stored nutrients, redirecting energy toward trichome production—it’s one of the key benefits of flushing. 

By stabilizing the internal environment and removing excess nutrients, flushing enhances cannabinoid and terpene concentrations, ultimately improving the potency, flavor, and overall smoke-ability.

Nutrient Lockout

If your plants are experiencing nutrient lockout due to overfeeding, they will absorb only what is necessary while excess nutrients accumulate in the soil. A thorough flush helps remove these surplus nutrients and salts, restoring balance to the growing medium. 

This process is similar to unblocking pores in your skin, enhancing the overall health of the plants. Flushing not only alleviates lockout symptoms but also refreshes the growing environment for future growth.

How to Flush Cannabis Plants

Let’s dive into our four-step guide on how to flush weed successfully, and with the right approach, you can ensure your plants thrive. But, before proceeding with the flushing process, it’s essential to gather the right equipment:

• Filtered, distilled, or Reverse Osmosis (RO) water.
• pH Meter and Calibration Solution
• EC/TDS Meter
• Watering Can, Bucket, or Hose
• Run-off Collection Trays or Drip Trays

1. Preparation

Proper preparation is vital for a successful flush. Start by using clean, pH-balanced water, targeting a pH of 6.0 and 6.8 for soil and 5.5 to 6.0 for hydroponics. It’s important to make sure you can test the pH level of untreated tap water and avoid flushing if you can’t make the right pH adjustments. Additionally, ensure your growing medium has good drainage to prevent waterlogging.

2. The Flushing Process

Begin by watering your cannabis plants with two to three times the pot volume, pouring the water directly around the apical mainstem. Monitor the drainage closely to ensure you see the excess water leaving the soil, as any remaining residues can be reabsorbed into the medium.

To evaluate the effectiveness of your flushing, employ a Total Dissolved Solids (TDS) reader, which will help you measure the purity of the run-off water that drains from your medium.

3. Post-Flush Care

To optimize the flushing process, repeat it every few days throughout the 14 days while carefully monitoring your plants for signs of stress or nutrient deficiency. After initiating the flush, you may notice that your cannabis plants start to take on a lighter color, and it is normal for some leaves to turn yellow as the plants mature. Conduct a final flush with clean water one to two days before you’re ready for harvest to ensure you remove any remaining nutrients from the soil.

Flushing in Different Growing Mediums

Flushing is a widely practiced technique in cannabis cultivation, and its effectiveness varies depending on the growing medium used—whether soil, coco coir, or hydroponics. Each medium possesses unique characteristics that influence nutrient retention and overall plant health. By exploring these differences, we provide valuable insights for growers looking to optimize their final product, ultimately leading to better yields and improved quality in their cannabis harvest.

Soil

Soil is a natural growing medium that supports a complex ecosystem of microorganisms, which can lead to slower nutrient release. When flushing soil-grown cannabis, growers typically need to extend the flushing period to allow the plant to absorb residual nutrients effectively. This results in more decadent flavors and cannabinoid content. It’s also important to monitor moisture levels throughout the growth cycle to prevent nutrient lockout and safeguard the plants’ health.

Coco Coir

Coco coir is a widely used growing medium that combines the advantages of soil and hydroponics, providing excellent drainage and aeration. Due to its lower nutrient density, flushing in coco coir is generally more efficient than in soil. Residual nutrients can be removed more rapidly, enabling a shorter flushing period. This efficiency helps maintain optimal conditions for cannabis plants during the flushing process.

Hydroponics 

Flushing is often more precise in hydroponic systems due to the controlled environment and targeted delivery of nutrient solutions. This technique rapidly removes excess nutrients, usually within a few days, leading to cleaner and more refined buds. However, it’s vital to approach flushing cautiously; if done too abruptly, it can stress the plants and hinder their growth and overall development. So, be mindful and attentive during the process.

Common Flushing Mistakes to Avoid

When it comes to growing cannabis, avoiding these four common mistakes can help you elevate your plants to their full potential without compromising on flavor or potency.

1. Flushing too early can negatively impact bud development, leading to lower yields with reduced terpene and cannabinoid content. On the other hand, flushing too late may cause your buds to taste more like dried hay, ultimately diminishing the overall smoking experience. Always remember that timing is crucial for optimal results.
2. Insufficient watering during the flushing process can result in residual nutrients remaining in the growing medium. To effectively remove excess nutrients, it’s vital to water with at least double the volume of your container pot. However, be cautious, as over-flushing can lead to waterlogging, which may cause unwanted stress.
3. Neglecting to monitor the pH level of the flushing solution can seriously affect nutrient uptake, so it’s vital to maintain an optimal pH range for optimal development. Additionally, skipping regular checks on plant health during the flushing phase may lead to nutrient deficiencies and stress. Don’t let your plants get lonely!
4. Customize your flushing methods for each specific medium to optimize nutrient removal and ensure that your cannabis plants thrive throughout the flushing process. By tailoring your technique, you can support healthier plants and ensure that your cannabis plants thrive during the flushing process.

Flushing vs Not Flushing: Chemical Analysis

While some growers argue that flushing enhances taste and eliminates excess nutrients, research suggests it may not significantly impact yield or potency. To explore this topic further, we’ve examined multiple studies assessing the effects of flushing on cannabis. These analyses aim to clarify how flushing influences yield, potency, terpenes, and overall quality, offering a thorough understanding of the potential benefits and drawbacks.

The University of Guelph’s study on Irrigation Management Strategies for Medical Cannabis evaluated the impact of flushing on nutrient concentrations in cannabis buds and found that flushing did not significantly lower nutrient levels in dried buds. Researchers noted that decreasing irrigation frequency saved up to 45.7% of water but had negligible effects on yield and cannabinoid profiles, demonstrating that, in this case, flushing did not enhance bud quality.

Rx Green Technologies assessed the impact of 14, 10, 7, and 0-day flushing periods on the yield, potency, terpenes, and mineral content of cannabis flowers. The study found no significant impact on yield or taste from the flushing duration. However, samples flushed for zero days showed improved flavor and smoke quality, while the 14-day flush increased iron and zinc levels, suggesting that there is no advantage to extended flushing for enhancing taste.

So, what are your thoughts? Do you support flushing, or do you oppose it now that you understand the process? We’d love to hear your opinions! Share your thoughts with us on our Instagram account. Until then, happy growing!