Is Flushing Before Harvest Necessary?

By Charlie Pearson

The Importance of Flushing a Hydroponic System Before Harvest

Have you ever heard about flushing your system before harvest? If you're wondering what flushing before harvest does and whether it's necessary (or not), you've come to the right place. In this guide, I'll cover what flushing actually is, what it does, and whether you should do it. So, without further ado, let's get right into it!

What Is Flushing?

Simply put, flushing your system means running it with just plain water and no nutrients. Even if you're a beginner hydroponic grower, you know that flushing your system helps remove salt build up as well as remove any chemical residues after cleaning your system (especially if you use bleach). So, why would you want to do that before harvest?

The main purpose of flushing before harvest is to allow your plants time to use up the nutrients they have already built up within them, which helps reduce the overall nutrient and contaminant load of your produce. It usually takes just a day or two since you're cutting nutrient supply to your plants immediately. This concept is not unique to hydroponics. Gardeners all over the world sometimes do this when growing in soil. Most of the time they simply water their plants and add no fertilisers for a week or two before harvest.

Benefits of Flushing Before Harvest

Proponents of flushing before harvest claim that it helps improve the taste and quality of your produce since it helps flush out excess salts, nutrients and contaminants. Other growers say it's actually counterproductive since you're robbing your plants of nutrients and once the nutrients have been absorbed by plants, they are there permanently and can't be flushed out, plus there aren't any conclusive studies confirming that flushing helps increase the taste and/or quality of the final product.

Growing crops both with and without flushing before harvest doesn't show a huge difference between them. Flushing is definitely helpful if you're experiencing salt build up or nutrient lockout. What many growers do is simply top up the reservoir with water once the plants are close to harvest. This helps save costs (because otherwise you would have to discard the nutrient solution and refill the reservoir with water) and still has a certain flushing effect (as you're not adding more nutrients and let your plants use the leftovers). Plus, you're not cutting your plants off nutrients all of a sudden, so it's not as much of a shock to them.

Should You Do It?

To sum up, I would recommend trying flushing before harvest for yourself and seeing if it helps improve the taste and quality of your produce. Depending on the type of nutrient solution you use, it might actually be helpful. However, if you follow the instructions carefully and change the nutrient solution and clean your system regularly, you shouldn't experience any problems, like salt build up or nutrient lockouts, so in this case, it likely won't make much of a difference. Alternatively, you can simply top up your reservoir with water once your plants are close to harvest, and this is a happy medium that still works as sort of a "flush" and also helps save costs and avoid water and nutrient wastage.