How to Properly Flush Your Crop Before Harvest (2024)

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Flushing is an extremely important part of the cultivation process. Most indoor crops have a lifecycle of around three months – two weeks for propagation, another two for the vegetative stage, and eight weeks for the flowering period. During this time, growers enrich their crops with base nutrients, vitamin supplements, bloom boosters, and more, each week scaling up their feeding ratios to ensure their plants are absorbing a heavy dose of carefully crafted elements. Fortunately for plants, these feeding programs are packed full of essential elements that maximize potential yields. However, a heavy harvest isn’t the only thing to consider – cleanliness is also a major factor that determines the quality of a crop. If you’re new to cultivation, read the following passage for a complete understanding of how to properly flush your crop before harvest.

What Is Flushing?

Flushing, or a flush, is a term used to describe the action of rinsing a plant’s root zone with excess amounts of water. As mentioned above, growers enrich their crops with an array of nutrients in all stages of growth. These nutrients, which are essentially a combination of different micro and macroelements, tend to build up in the soil system over time. This accumulation of minerals happens not only in the root zone but also within the plant itself. While high levels of nutrients are needed to accelerate plant growth, the build-up of primary minerals such as nitrogen, calcium, phosphorus, and potassium in freshly dried flowers can often leave the product with a harsh, bitter taste and blackened, tar-like ash. To avoid this upset, growers will often flush their crops to wash out minerals that have built up in the root zone over time.

How to Properly Flush Your Crop Before Harvest

1. Start to flush 10-14 days before harvest
2. Flush your plants until run-off
3. Test the run-off samples and log the data
4. Use beneficial bacteria
5. Monitor your crop

#1: Start to Flush 10-14 Days Before Harvest

There’s an industry consensus that plants in soil/soilless substrates need at least a 10-14 day flush. So, time your harvest correctly, and make sure to cease the use of plant food approximately two weeks before your crop’s harvest date. Or, follow the recommendations on your established GreenPlanet feeding program. For growers not using a feeding program, this mark will likely be around the sixth week of flower. However, if you’re managing a strain with a longer flowering time, be sure to consult strain-specific growing guidelines to ensure your crop has an adequate flush without becoming over-ripe.

#2: Flush Your Plants Until Run-Off

The best way to completely saturate your medium is to water your plants until run-off. Start by watering your plants with plain, neutral water (with a pH of 7.0) until roughly 20% of the water runs out of the bottom of your container. For example, if your start by watering your potted plants with 1 Litre of plain water, at least 200mL should run out of the bottom of your container. This action will guarantee the flush of built-up sediment and mineral salts.

#3: Test the Run-Off Samples and Log the Data

If you want to be sure you’re flushing correctly, simply collect the run-off and test the samples with a conductivity meter. Start by flushing your plants until 20% of the water runs out of the bottom of your container. Then, collect some of the water in a container and test the sample with a conductivity meter. Finally, log the data and repeat the process every time you flush your plants. The data will ideally indicate a rapid decrease in salt concentration over time, meaning your plants are slowly flushing concentrations of salt away from the root zone, and are therefore becoming cleaner in the process.

Definition: Electrical Conductivity (EC)The relative strength or concentration of a solution, or its ability to conduct an electrical charge. Other measurement solutions include the Parts Per Million (PPM) scale and/or Total Dissolved Solids (TDS) estimations. How Does EC work?Salt emits an electrical charge (electrolytes) when in a solution. By testing the conductivity of that charge, you can get a reading of the relative strength of the solution.

#4: Use Benefical Bacteria

#5: Monitor Your Crop

It’s completely normal for plants to undergo physiological changes during the flushing period. In fact, it’s positive that certain changes take place. Since your crop is nearing the end of its lifecycle, it’s common for growth rates to slow, and for new colors to emerge. Also, due to the lack of nutrition during this stage, it’s likely that old foliage will begin to yellow and die off. But don’t worry, this is a normal transition sometimes referred to as “autumning-off”, or the process of a crop expressing autumn colors during the flushing process. Overall, the changes above are a good sign that your plants are nearing maturity.

Whatever your style of garden, chances are, GreenPlanet Nutrients has the perfect base nutrient program. To access the programs available at GreenPlanet Nutrients, contact a member of the GreenPlanet sales team, or your local garden supply store for product information and purchasing inquiries.

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