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Clean Out Your Crop With Proper Flushing Techniques

Be sure to flush your crop properly for the best results come harvest time. Be sure to flush your crop properly for the best results come harvest time.

In order to maintain optimal growing conditions and produce tasty consumables, growers must understand the basics of flushing.The problem most growers face is the overwhelming amount of information and misinformation on flushing.

Although methods of flushing may differ from grower to grower, the concept behind why and when growers flush remains fairly consistent. Before we dive into the actual flushing process, let’s first define what flushing is and when and why it must be done.

Flushing is essentially a cleansing of the plant’s root zone, including the medium itself (if any) and the hydroponic reservoir. Unfortunately, defining flushing in terms of indoor horticulture is confusing in itself. This is because the term “flushing” is used to describe two different procedures in an indoor garden: flushing during the plant’s life cycle and flushing before harvest.

Flushing DURING the Plant’s Life Cycle

Flushing is a common solution to solving problems that occasionally occur during the plants life cycle. In situations when there is a lack of runoff, nutrients can build up in your growing medium leading to issues like nutrient lockout. Many growers mistake the signs of lockout, like leaf discoloration, for a deficiency and will try to correct by adding more of the individual nutrient which appears to be missing. This of course causes the problem to become even worse. A flush will allow you to purge the buildup, so that your nutrient regimen can again be properly up taken by your plant.

Flushing in Soil

The biggest mistake growers make when flushing is that they don’t put enough flushing solution though the soil. First, elevate the planting container so that the runoff can go to waste and not be wicked back up by the plant. Pour a significant amount of water through the planting container until there is a noticeable lightening in the color of the runoff water. The solution poured though the containers can be straight water, a flushing additive, or a diluted mixture of the nutrients being used (1/8th the regular strength). Flushing with a flushing agent or with diluted nutrients is usually more effective than plain water at drawing the excess salts out of the soil.

Flushing in Hydroponics

Flushing in a hydroponic system will depend on the particular type of system being run. With deep-water culture, current culture, NFT, aeroponics, or other hydroponic systems where there is virtually no medium, a flushing can be done by simply changing the reservoir solution. Top-feed, ebb-and-flow, soilless, or rockwool hydrogardens will require flushing that is similar to the requirements of soil. Growers with these systems can add straight water, a flushing additive, or a diluted mixture of the nutrients being used to the reservoir and then run the pump for 10 to 20 minutes. This should be done when the lights are off so that the feeding of the plants is left uninterrupted.

Flushing Before Harvest

When flushing is referred to in regard to harvesting, it can be defined as a cleansing of the medium or reservoir, with or without the aid of an additive, and the withholding of all or most nutrients for a short period of time leading up to harvesting. Flushing before harvesting is essential to the removal of excess salts built up in the medium and the plant itself. By withholding nutrients during the last seven to 10 days prior to harvest, the plant is forced to use the remaining nutrients in the medium and then some of the reserves within itself. Consumables are safer and have smoother flavors when proper flushing has been implemented.

There are many techniques growers use during the final flushing of their plants. From flushing additives to fruit juices, growers have tried just about every technique possible in order to accentuate the flavors and aromas of their plants.

For the final flush before harvest, the best thing a grower can do is to experiment a little with the amount of time and type of additives used. Some varieties of plants will respond differently to different flushing techniques, so it is important that growers are able to slightly change their technique depending on the plant variety, if necessary.

Newbie growers or growers who want to stay on the safe side should flush a good week or more before the projected harvest date to ensure an adequate flushing. As growers get more harvests under their belts, they will find the particular flushing method that works best for them and their plants. No matter how well a garden is grown, without a proper flushing at harvest time, the fruits of a grower’s labor can end up tasting like garbage.


Don’t underestimate the importance of a proper flush before harvesting. High-value plants that are not properly flushed will retain excess salts, which cause unpleasant flavors.

Do experiment with different flushing procedures and durations, especially when growing a variety of different plants. Each variety of high-value plants will have slightly different needs for the pre-harvest flush.

Don’t add fruit juice concentrates or any other raw carbohydrate sources to a hydroponic reservoir during the flush before harvest. Many of the carbohydrates available at the local hydroponic store will better suit your plants than the raw carbohydrate sources.

Do use water, diluted nutrient solution, or flushing additives to flush during the plant’s life cycle. When using any flushing additive, make sure to closely follow the manufacturer’s directions. Many flushing products have slightly different instructions. Failure to follow these directions precisely could make the difference between a good or bad tasting product.

Do leave Advanced Nutrients’ Final Phase in the reservoir during the last week prior to harvest. Final Phase is the only flushing additive on the market that can be left in the nutrient reservoir for the final days of the plant’s life.

Don’t use flushing agents during the garden’s light cycle. During the light cycle, plants will attempt to uptake the flushing additive. This is really bad for the plant itself, not to mention the horrible flavors it invokes (the exception to this is Advanced Nutrients’ Final Phase, which is designed to be absorbed by the plants).

Do flush at any sign of nutrient lockout or at transitional times throughout the plant’s life cycle (such as when they change from vegetative growth to blooming).

Don’t use any plant-hormone-based product as a flushing agent or during the final week before harvest. Excessive plant hormones in the late stages of blooming could cause the plant to revert back to vegetative growth.

Don’t flush plants in soil containers that are already overwatered unless a nutrient lockout has occurred. Choose to flush soil containers only when they have naturally dried out.

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This video contains tips on flushing your crop.
Last modified on Thursday, 10 October 2013 19:25

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