Originally Posted by emilya
Zandor was a wonderful resource on this board... I would love to know what happened to this guy. I too learned a lot from reading his writings here at c.com.
Here is what I know about flushing.
There is a point about 5 weeks into flower using FoxFarms nutes and soil where you just have got to flush. You see the plants go from a stable wet/dry cycle to something noticeably longer, almost overnight. Your girls are locked up at that point, with way too many salts in the soil. This makes total sense, since right before this the FF schedule has you throwing the entire line at them for 2 weeks... so it is flush time. If you watch your wet/dry cycle carefully, you can see when this time is.
The other time that you flush, as Zandor reminded, is before you harvest so that you do not have to taste the chemicals in your end product. This takes at least a week of plain water, and some do 2 weeks of just plain PH'ed water at the end after the final flush.
Here, I do a 1.5x flush in the middle and a full 3x flush at the end, one week before harvest. The 1.5 and 3x is the volume of water per container size... at the end, a 3gal container gets 9 gals of water. Also, my city water is a bit over 7.0ph part of the year and 7.2ph during others. I use plain white vinegar from the grocery store as my PH down all through the grow, and I have found that vinegar is also an effective add in to remove salts more effectively than just plain water, so this works very well to provide an effective flush in my garden.
Now, I have been speaking as a soil farmer, but if you grow using hydro the rules change and you are changing solutions every 2 weeks. The flush at the end however would still seem to be very important to me and I would adjust accordingly.