Learn About Hydroponics

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Do You Need to Flush?


Most growers flush at some point - but when and for how long should you do it? Here's what you need to know.


What's flushing?


It’s where you apply nothing but water to your root zone (absolutely no nutrients at all).


When do you flush?


It’s common to flush plants in the final stage of growth, typically the last 1-2 weeks.


Some growers also flush for 1 – 2 days mid-cycle.


Why flush?


Flushing at the end


It forces plants to use the nutrient stored up inside them.


If unused or in excess, these nutrients can alter the taste and quality of the final yield.


Some growers also find that flushing at the end helps bring out preferred characteristics – like a slight colour change.


Ultimately, by flushing at the end, you’re making sure it’s the final produce you’re tasting, not stored nutrients.


Flushing mid-cycle


Flushing for 1 – 2 days reduces nutrient intake quickly. Some growers flush mid-cycle to correct damage done by overfeeding. You can do this at any point of growth.


Some growers also flush for 1 – 2 days when switching to a flowering cycle. Doing this quickly rebalances the preferred NPK ratio in the growing media ready for the change in growth.



Do I always need to flush at the end of a crop?


There’s some debate.


Some people argue that it depends on the type of feed and growing method you use.


Most people agree that if you grow organically, flushing isn’t as important as it is when you use mineral based nutrients.


There are also some flush products. Some help plants use excess nutrients, others make flushing easier by binding up nutrients in the media.


The one that we sell is Canna Flush. It draws out and holds onto nutrients in plant tissue & growing media, so that it's easier to flush out.

Canna Flush

How do I flush?


It’s as simple as just feeding plants water.


If you grow in a hydroponic system that doesn’t use media, flush for around 7 days at the end of your harvest.


If growing in a media (like soil or coco) you need to start earlier to ensure the nutrients that have built up in your media will be flushed out too.


Most people using media start 2 weeks before harvest. Or you can halve the nutrient strength in the second to last week, then move onto water in the final week.


You can cut down the flushing time by using SHOGUN Dragon Force, an end of flowering booster that adds weight to your final harvest. You'll still need to flush for one week though.


SHOGUN Dragon Force


How do I know I’m flushing for long enough pre-harvest?


Flushing is a bit of a balancing act. Flush for too long and it can hurt your yield. Too short and your flavour is poor.


When flushing for the right amount of time, lower leaves should turn yellow, or even a red-brown colour. This’ll happen roughly halfway through your flush.


This fading out of the older leaves is a sign that the nutrient reserves are being used up and transported inside the plant to the developing fruits and flowers.


What’s a flavoured flush?


Some companies sell flavoured flush nutrients that they claim adds a flavour (like pineapple or blueberry) during the last two weeks of flowering. These are mostly available in North America.


We don’t believe they work.


Ultimately, flavour is determined by your plant’s genetics. You can make the flavour stronger, but you can’t change it altogether.

Is there an alternative to flushing?


Yes. You can slowly work down your nutrient strength over the last 3 weeks of your crop instead. Start at week 6, where the nutrient solution will be around 1.6 EC (16 CF), and work it down to:


• End of week 6 - 1.4 EC (14 CF)

• End of week 7 - 1.2 EC (12 CF)

• End of week 8 - 0.6 EC (6 CF)


By keeping it low at this time (while plants are maturing) you lower the risk of excess nutrients being stored in the plant at all.

Flushing media

Are there any down sides to flushing?


Only if you over-do it mid cycle.


Some growers panic and flush too heavily, for too long. Make this mistake and you can go the other way and underfeed plants!


If you’ve overfed plants and the leaves are just starting to curl over or burn at the tips, go easy! Try using a half strength nutrient solution instead of applying lashings of water.


Doing it slowly like this causes less osmotic stress.


The best method, of course, is not to overfeed plants in the first place!


If the EC rises in a recirculating hydro system, plants are using less nutrients and more water. Reduce your nutrient strength before plants get overfed.


In a hand-watered or drip system you can check the EC of run-off. If it’s higher than normal, either get more run-off when you feed or reduce the nutrient solution EC.

This post was posted in Growing Tips, Nutirents & Boosters, Nutrients, Your First Grow


6 Comments - Add Comment

  • John N
    Posted January 15, 2017 at 10:55 am
    If you're using General Hydroponics "Flora" series then you run FloraKleen through your hydro system for 24 hours once every 15 days.

    I use it when I do a complete nutrient change (pump out/refill) about once a fortnight.

    That keeps drippers/airlines clean and prevents any build-up of salts/nutrient lock-out. For soil its a drench every 15 days.

    You can use it for a final flush but IMHO it isn't required provided you've been using it throughout the grow. Final flush isn't practical for things like tomatoes which will grow continuously until you kill them/frost gets them.


  • Jay
    Posted December 15, 2016 at 10:22 am
    Flushing is the biggest myth ever started do the commercial growers in greenhouses grower our food crops flush? Most grow in rock wool cubes and can feed anyway up to 40 times a day via drippers that's to ensure no nutrient build up as the plants are receiving a constant supply of fresh nutrients. The problem with a lot of growers they over feed and that can affect the final product or if you let your medium dry out your mineral nutrients can crystallise. The only good advice on there was to reduce your ec most Dutch growers will reduce this by half there max ec in the last week that's it. If you read this don't just dismiss it because everyone goes on about flushing try it and also you will notice a big difference in your yield why take food away from a plant when it needs it I don't think your plant likes to be flushed whether your feeding mineral or organic the plant just wants food!
    • Replies

    • Mrsj
      Posted January 2, 2017 at 9:39 pm
      Actually, flushing makes the plant use up all the nutrients and sugars up from the leaves. The taste of anything you grow will be very different if you do not flush. Thats from personal experience and years of learning. Don't do it if you don't want too,but also,don't rubbish it until you understand why its done and what difference it makes.

  • Derek Morris
    Posted December 13, 2016 at 12:18 pm
    Nice information. I'll try the middle cycle flush next time as I use Coco. Great tip.
    Thanks Growell!

  • RICHARD Scott
    Posted December 12, 2016 at 11:10 am
    Excellent article.. been at it forva while now and always flush for the last week pre harvest. Deffo changes taste for the better.

  • Paul Sleczka
    Posted December 12, 2016 at 10:21 am
    This was very informative as I'm a newish grower and my latest attempt has leaves that have gone brown. Thank
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