How to prevent seedling stretch after germination?

[kronik]

High all, I use Grodan's recommended germination method (rockwool starter plugs, tray on top of tray with water, humidity dome, heating mat, etc.) and so far I am at almost 100% germ rate with this method (no presoaking, paper towel etc.) so I am pleased.

However, it seems that one day I will look and see nothing, the next day I look and have super stretched germinated seedlings! I use a 400w CMH bulb at about 18" away (which I read is good to start with) and I have plenty of wind blowing so I don't think it is due to any of those reasons - it's like they just come out that way.

The worst part is they topple over so then I have to quickly transplant to soil so I can keep em upright. Am I missing something?

Thanks in advance!!

kronik

 

[hoosierdaddy]

I would have thought that a 400 that distance would not stretch seedlings. (shrug)

Anywho, if it were me, I would go with flouro tubes or cfls for seedlings.
The bluer light models will help to keep things tight, and the closer you get with the light without burning, the better.

But it looks like you still have the dome on. I always take the dome off as soon as the cots are in the air. And just enough air flow to make them wiggle a little is plenty.
The plastic is really going to diffuse the light and help them want to stretch.
I've always found it better if the seedlings are in the same environment as the rest of the vegging plants. Not under a dome with a fan on them. If the environment outside of the dome is a bit harsh, that may be where you need to most work.

 

[WaterFarmFan]

It might be the rockwool - I would try switching to rapid rooters.

 

[andrew415]

18inches seems a bit to much to me?

I kept mine about 5 inches away but I was cool tubed, so maybe go down to about 10 inches and feet how hot that is?

 

[smokeymacpot]

stretching = stretching towards the light. so bring them closer
dunno how much, as i use cfl 1" away

 

[FRANKENBLUNT420]

I would have thought that a 400 that distance would not stretch seedlings. (shrug)

Anywho, if it were me, I would go with flouro tubes or cfls for seedlings.
The bluer light models will help to keep things tight, and the closer you get with the light without burning, the better.

But it looks like you still have the dome on. I always take the dome off as soon as the cots are in the air. And just enough air flow to make them wiggle a little is plenty.
The plastic is really going to diffuse the light and help them want to stretch.
I've always found it better if the seedlings are in the same environment as the rest of the vegging plants. Not under a dome with a fan on them. If the environment outside of the dome is a bit harsh, that may be where you need to most work.

i would have to agree with this one, sounds about right. they need to harden off to really tighten up, so maybe too much humidity is a bad thing

 

[Bulldog11]

The only other thing it could be is your heat mat. Do you have a thermostat on that bitch? Any temps above 85 will cause major stretch. Peace.

 

[JohnnyToke]

those rockwool starters cause all kinds of problems for me. I switched over to peat pellets and have no more issues. I grow hydro so when the plant is well rooted in the peat pellet, I bury it in hydroton just like I would the rockwool cubes.

works great and the pellets are cheap and readily available.

I also use them for my mom plants that I keep in soil. once rooted, just bury in your favorite grow soil.

regards,
JT

 

[Country Mon]

I agree with the others about most of this. Rookwool is, um... overrated. RapidRooter plugs are great, you may want to give them a try. Nothing compares.

As for the seedling heat mat... why use one? Are your room temps below 75 degrees F? I'd get rid of the mat and just concentrate on keeping your room temp at 78-82 degrees continuously. You don't need wind at this stage, either. You also don't need a dome for seedlings, just clones.

I also don't really get the 400 watt approach with starts and seedlings. A bank of florescents (get the 6000K bulbs) will do the same thing better for half the electricity/price. Important: run the lights 24/7. Dark periods can cause stretch with some strains. Also, get the 'lings about 8" away from the floro bulbs. Use the MH after the first week or 10 days; seedlings and clones don't need/like the intensity.

 

[NorCalFor20]

I have a 400w cmh and i keep mine 4" away from the tops of my plants, but your seedlings are so young id would do like 8-10" and try that.


either way seedling stretch isn't that bad mine stretched and the part that stretched is now (28 days later) a 2" thick tree bark! ready for those heavy buds....

with your 400w you should be looking like this in a months time.... its my first grow too. and these pics were tooken at 24 days.

 

[kronik]

Thanks for the excellent replies all!!

Here's some more details about my grow environment:

I'm growing in a closet using an aircooled 400w CMH bulb.... temps started off too high (85-87).... then I read an excellent post about an "ultrasonic fogger" and now through the use of 2 of them, I've got the temps down to the mid 70s!!

Of course, this raises the humidity a lot as well - my humidity ranges from 60-70% - I believe this is good no?

The humidity while the seedlings were under the dome was 80% however... temps were about 79.

This is what I have been thinking for the next time:

1) I've always read to germ in total darkness.... I dunno if I buy into this as obviously in nature the sun is still out while the seed is germing in the earth. So for my next time I was thinking of leaving the light on right so that the instant they poke through they "see the light" and hence no need to stretch.

2) hoosierdaddy - agreed, the next time the dome is coming off as soon as I see the first cots.

3) WaterFarmFan, Johnnytoke, Country Mon - my very first grow attempt was with rapid rooters and it failed miserably - I moistened them thoroughly and by the time I woke up the next morning they were like dried cat turds. Rockwool holds water like a camel - after 3 days my cubes are still moist!

4) Light Distance

andre415 - regarding the distance, what kind of light were you using? I am using an aircooled CMH so yes, it does run very cool - I can put my hand at about 6" underneath and it feels fine.

However, I read that for seedlings you don't want the light too close as they can't handle the par intensity (regardless of the heat)??

NorCalFor20 - Did you start off with the 400W CMH for your seedlings?

5) HEAT MAT

Bulldog11 - I never read that about the heat above 85 causing major stretch? I had the heat mat thermostat set to about 83ish (as the grow room itself is in the mid 70s).

 

[clowntown]

It's not the rockwool!

85F is a tad high, but it's primarily the distance from the bulb.

Also, take the dome off. You don't need a dome for anything with roots, and is actually detrimental in most cases.

 

[bongorilla]

I'd make sure when I took that dome off i'd do it gradually. 1st jack up 1 side and leave it for air flow then 12-24hrs later jack up the other side and finally take it off.
going from super hi humidity to low humidity can damage young plants and clones sometimes by drying out the foliage.

I usually get that stretch with seeds unless I put them in a garden window or direct sunlight helps minimize it a lot.
at transplant i just bury em up to the first leaves.

if the plants start falling over a pipe cleaner or wire twist ties make a good support stake.

 

[TREE KING]

guys im about the buy this light for seedling and clones. t5-8 lamp
http://www.hydroempire.com/store/product_info.php/cPath/3_28/products_id/1122
how high from the dome should i keep the light while germinating seeds? i also dont want them to stretch either.

 

[hoosierdaddy]

TK, You can leave the light completely away from the dome until they pop. Then take the dome off to fix your lights up. You can get T5's pretty close, especially if you have a light breeze going over top the youngins.

And I agree with the bongorilla...crack it at first and let them harden up a bit.
Try it next time without a dome.

NorcalFor20, is that shot with the ruler the bagseed? Looks like you might be growin some kind sativa there my brother.

 

[TREE KING]

hoosierdaddy, how close is pretty close? im so used to the regular flourescents sitting right on top of the dome. i seriously have no idea how close they should be. how many inches or feet away from the plants you think?

 

[smokeymacpot]

This is what I have been thinking for the next time:

1) I've always read to germ in total darkness.... I dunno if I buy into this as obviously in nature the sun is still out while the seed is germing in the earth. So for my next time I was thinking of leaving the light on right so that the instant they poke through they "see the light" and hence no need to stretch.

ahh....

my seeds are germed in soil and they get light as soon as they break the surface, if i wait a day before they get light, they can stretch as much as 5cm in one day!
so yes please dont sit your germing seeds in the dark.

 

[hoosierdaddy]

Tree King, it has lots to do with the temps. I would probably put the tubes 4-5 inches above the tops and see what my temps were between them. I don't think seedlings should see much more than 80degF. If my temps were OK, I may lower them another inch or two.

Once they harden up a bit, you can get the lights within a couple inches (providing you have a light breeze goin on), but I have seen seedlings do just fine when they were many inches from the flouros.

 

[Pipedream]

It's not the rockwool!

85F is a tad high, but it's primarily the distance from the bulb.

Also, take the dome off. You don't need a dome for anything with roots, and is actually detrimental in most cases.

Short, sweet, and on the money! Couldn't have said it better myself.

 

[mrniceguy]

How deep do you plant them?