Need to flush in handwatered rockwool?

[King Tubby]

I presently have about 20 plants started from seed (Kali Mist, PoG, Hashberry, Haze x Chronic) that I have in quart Kord pots. The mix is rockwool mini cubes, perlite and a pinch of fine vermiculite.

They've been feed PBP with Cal-Mag and LK. say 12-18" tall with 5mg Cal, 12-15 PBP and 10-15 LK per gallon.

Showing some slight tip burning and mag/cal defs (whichever one where the margins of the leaves yellow then brown).

Should I be flushing this mix with 5.5 pH'ed water every now and again? First time with rockwool; I'm a NFT/amended-dirt organic head most of the time.

 

[fishheadbob]

I don't feel that the occasional flush hurts anything; it's usually beneficial. I use 4" rockwool cubes and suspect that they might accumulate ferts and salts over time, so I give my cubes the occasional clean water bath as a detox measure.
Over fertilization is a common problem, you may be experiencing this with your tips. Check out the cannabis infirmary, My Name Stitch has a great long post with diagnostic photos which I find very helpful.
I also like to go light on nutrients. Seems to me that results good or bad become evident quicker in hydro without the buffering effects of soil, mistakes can come on fast. I also feel that nutrient companies are in the business of selling nutrients, and maybe their ppm recommendations are on the high side to sell more product?

 

[FirstTracks]

rockwool should be flushed at least once every 2 weeks to avoid salt buildup

 

[Whatever]

rockwool should be flushed at least once every 2 weeks to avoid salt buildup

That's not my experience with rockwool. If you're running too high an EC then maybe so.

 

[phatnuggetz]

I would flush, it cant hurt.

 

[BENJI]

as my mate says, if in doubt flush it out!!!
phatnuggetz is right flushing wont hurt..

 

[franco.gh]

The system of flushing is not only good for removing excess salts. It also allows you to create a rhytm of wet-dry-wet that contributes to maximize oxigen to the root system and feeding intake.
;-)

 

[King Tubby]

The system of flushing is not only good for removing excess salts. It also allows you to create a rhytm of wet-dry-wet that contributes to maximize oxigen to the root system and feeding intake.
;-)

Thanks everyone.

I was away this weekend and came back to some explosive growth and bone-dry rockwool! Slight wilting. Since I lost some plants a year ago due to drying out, I've been watering more than necessary I think. I recount reading somewhere that over-watering can contribute to/mimic nutrient deficiencies.

I'm going to flush with some 5.5 pH water every two weeks I think for the hell of it. I mean, with the hand watering you always get a healthy amount of runoff; this isn't like some 4" cubes sitting in the same solution all the time.

 

[Whatever]

The system of flushing is not only good for removing excess salts. It also allows you to create a rhytm of wet-dry-wet that contributes to maximize oxigen to the root system and feeding intake.
;-)

I disagree with that...you don't want wet-dry cycles in rockwool. Just the action of solution draining creates a lot of oxygen availability in the root zone and if your starting solution is well oxygenated, high ppm DO content, it wouldn't matter how often you water. For one when rockwool dries out your EC in the root zone goes up.

I've been watering more than necessary I think. I recount reading somewhere that over-watering can contribute to/mimic nutrient deficiencies.

How often are plants watered in DWC? I ran rockwool slabs for a few years and had great results running 4 30 minute feed cycles per lights on. Problems easily arise when you're running too strong a nute solution for starters.

Anyway...never 'flushed' this stuff and at the end just stopped feeding. I always kept it wet.

 

[paulobaca]

That's not my experience with rockwool. If you're running too high an EC then maybe so.

Only a noob but I agree with whatever. Since you have overfeed signs I would say try to flush but "flushing for the sake of flushing" is not required for RW IMO.

 

[paulobaca]

There is a lot of misinfo on RW regarding things whatever mentions. I started 15 months ago and did extensive searches for RW info and encountered a lot of BS.

If there are roots coming showing on the bottom of the pot you should start watering more frequently. RW growers water rooted plants anywhere from 1-8 times a day.
Even when RW is wet there is still a lot of oxygen in there so once the plant has prolific roots dont be too scared to water.

The wet dry cycle is for soil- letting RW get to dry will destabalize RW EC/PH and plants will probably suffer.

Really with RW I think the periods during which you should worry about over watering are with unrooted/barely rooting seedlings/clones and for a couple of days following a transplant.

Pot size should also have something to do with water frequency too. If they are in a oversized pot for their size you may want to try 1-2 times a day. Now if we were talking a 3 foot plants in a four inch RW cube you would want to water much more.

 

[Whatever]

There is a lot of misinfo on RW regarding things whatever mentions. I started 15 months ago and did extensive searches for RW info and encountered a lot of BS.

If there are roots coming showing on the bottom of the pot you should start watering more frequently. RW growers water rooted plants anywhere from 1-8 times a day.
Even when RW is wet there is still a lot of oxygen in there so once the plant has prolific roots dont be too scared to water.

The wet dry cycle is for soil- letting RW get to dry will destabalize RW EC/PH and plants will probably suffer.

Really with RW I think the periods during which you should worry about over watering are with unrooted/barely rooting seedlings/clones and for a couple of days following a transplant.

Pot size should also have something to do with water frequency too. If they are in a oversized pot for their size you may want to try 1-2 times a day. Now if we were talking a 3 foot plants in a four inch RW cube you would want to water much more.

I think in general that's good info and nice clarification on some points. Keeping things on the dryer side, not really dry, does help drive roots down but it doesn't take long really. Whenever I transplanted freshly rooted clones to something like 3 or 4" cubes I soaked everything well and didn't water again until they got pretty dry. The solution those cubes got soaked in to prep em was pretty weak so no crazy pH/EC swing as they dried.

Once I dropped the well rooted cubes onto slabs would only run a cycle or two per day through the slabs just to keep em fresh. I top watered the cubes during the initial few days waiting for roots to drive into the slabs.

I never worked with seedlings in RW and never interested in doing it either.

but "flushing for the sake of flushing" is not required for RW IMO

Yup