Flushing Coco pre-Flowering

Hi All,

I’ve been growing for a few years now in coco coir. I wanted to get your opinions on flushing because most of my knowledge is trial and error. I am new to ILGM but have used other forums previously. The community seems fairly smart and friendly here so I want to pick your brains.

Hydroponic Coco

How often do I water and how do I determine when to water: water daily, the amount is based on the weight of the medium

Indoor or Outdoor: indoor

Room size: 2x4

Light system: SF1000 and Vipar XS1000 (better of the 2 IMO)

Temps; Day, Night: 75

Humidity; 55

Ventilation system; fans

AC, Humidifier, De-humidifier: no

Co2; NO

Currently, I flush for a week with distilled water when I flip to flower. My thinking is to get all the remaining nutrients and salt out of the medium before switching to a flowering nutrient profile. I have had issues with salt poisoning in the final weeks of flower nearly killing my plants.

I’m simply looking for your opinions on my practice and any feedback or advice you may have.

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just a pic of the current plants


I started in coco coir. Was really interested in a hydo grow. I found that with the introduction of bacteria and microbes, my plants did better. I now add about a quart of composted manure or worm casting for every gallon of medium.

Sounds like experience talking and you have a good plan.

Can you define the flush for a week part…? Do you mean water to runoff as needed for a full week?

That feels like you’re depriving them of much needed nutrients for a pretty extended time.

If you really want to “clean the slate” you should be able to accomplish that in one large flush then immediately push in the flowering nutrients. Flushing won’t take nearly as much water as soil would.

@Nicky has a lot of coco experience and may be able to chime in though he’s runs autopots.


Good advice

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My question is what nutrients are you using? Secondly, when you feed, what is it’s ppm and do you feed / water enough to produce 10 - 15% runoff (maybe not every time but often enough to monitor runoff ppm & pH).
Like to see a photo of the salt poisoning.
I am in line with one thorough flushing followed with nutrients.

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Coco should be watered/fed daily to get agood amount of runoff with the proper ppm and ph going in, this removes the unused salts you’re concerned about. If you water daily to runoff you are flushing each time, coco offers nothing for the plant nutrition so have to fee every time you water. With some nutrient lines this can get expensive and lend themselves better to a recirculating system. For coco jacks 321 is popular as not harsh on plants and is reasonably priced and easy to use. Since I switched I’ve brought three harvests to completion and 2 other grows are coming along nicely. Doing this for a few years you probably already know this and likely way more than me but I’m happy to share what I know and discuss what I think I know.


With mature plants i would feed to runoff every day at or around time lights come on. Unless there is some kind of issue or you’rein larger pot than you need to be, they will be about dry same time the next day

You can do this without seeing deficiencies? I gave one straight watering to my plants with distilled last grow, within 36 hours my plants were screaming for calcium. May be a difference in how hard plants are pushed in my grow vs yours, but I couldn’t see getting away with maybe 1-2 days of straight water in the middle of a grow. I also run pretty much same npk ratio and concentration (+/-1000ppm) from start to finish on my coco grows. I’m not sure it provides the most successful results, but it definitely works pretty good.

Issues with coco could easily be just coming in with too high of ppm, not feeding to enough runoff, or allowing it to dry out. But it’s not exactly easy to overfeed by frequency in coco. In the right conditions coco can be fed full strength nutrients multiple times a day.


WOW so much feedback, thank you for all the input.

A common point I seeing being brought up is RUNOFF. How much liquid runoff should I have after feeding? I suspect I run a little drier than most of you which could be why I may be facing certain challenges.

For nutrients, I’m using GH 3 part (Gro,Bloom,Micro). consistently around week 5 of flower my fan leaves start drooping and turn this DARK green/purple. The flowers stop growing and the leaves get tip burn.

I am not in the practice of measuring runoff (shame on me I know) but it is something I have started doing.