Advice on a seedling potting mix for a frequently flooded seedling system

[Kobus Jooste]

I am converting a small section of my mixed system to house 30 seedlings at a time for new plant establishment.  It will be connected to the existing flood and drain system, which means getting flooded every hour.  I would like to know if there are suggestions out there for a media mix for the seedling pots that will work under these frequent flooding events.  I'm scared of rotting seedlings and was thinking down the line of a mix of sand and coir / coco peat.  Any suggestions? I really want to keep to the pumps I already have going and am trying to avoid putting in another one just for the seedlings.

[TCLynx]

uh, bark chips maybe?

 

Actually instead of flooding and draining the seedlings, perhaps some sort of capillary matting set up might be more appropriate to something in a potting mix.  I simply have a shelf with liner where there is water in a gutter beside it and the matting hangs off the shelf into the gutter of water to wick moisture up to the shelf and the seedlings sitting on it.  Seems to work for seed flats, peat pellets, soil blocks and even small (up to say 10 cm) seedling containers so far.  I've also done this on top of a raft without holes too.

[Kobus Jooste]

I have seen your wicking bed and it is really nifty.  I have a small bin already plumbed in (used to be a small duckweed bed) that I want to fill with gravel.  It is a bit shaded, and ideal, I thought, for seedling establishment apart from the flooding regime it will be exposed to.  I was hoping that using a rather "open" mix would allow seeds to germinate without rotting.  Seeds germinate if I just lob it into the gravel.

TCLynx said:

uh, bark chips maybe?

 

Actually instead of flooding and draining the seedlings, perhaps some sort of capillary matting set up might be more appropriate to something in a potting mix.  I simply have a shelf with liner where there is water in a gutter beside it and the matting hangs off the shelf into the gutter of water to wick moisture up to the shelf and the seedlings sitting on it.  Seems to work for seed flats, peat pellets, soil blocks and even small (up to say 10 cm) seedling containers so far.  I've also done this on top of a raft without holes too.

[TCLynx]

I've done compost mix in pots dug into gravel beds so just the bottom inch of the pots touch the water on the flood cycle.  Seemed to work for many things except that some critters tended to dig up the pots in search of worms to eat.

[Kobus Jooste]

I was wanting to go for that kind of thing.  Water level will be at the top of the gravel, and then lifting an inch every flooding cycle - just enough to wet the bottom 1/2 of the seedling tray.  I figured if the media is coarse, it will not become waterlogged but the seeds will still germinate.  Can only give it a try and see.

TCLynx said:

I've done compost mix in pots dug into gravel beds so just the bottom inch of the pots touch the water on the flood cycle.  Seemed to work for many things except that some critters tended to dig up the pots in search of worms to eat.

[TCLynx]

Yep.

 

You may find that some types of seeds germinate and get going fine while other seeds need more drying.  Might be as simple as adjusting the height the tray sits in the bed so the seeds that want drier only the bottom 1/2 cm gets wet while the seeds that don't mind wet could sit lower and the bottom 1/2 of the tray would get wet.  Stuff like lettuce will germinate in waterlogged conditions while I think spinach wants a bit more drying.  Of course spinach can be challenging to get to germinate well in hydroponic situations.

[Kobus Jooste]

Will give it a try soon.  Almost done with the gravel (ran out).  Will want to try to germinate onions and lettuce first. 

TCLynx said:

Yep.

 

You may find that some types of seeds germinate and get going fine while other seeds need more drying.  Might be as simple as adjusting the height the tray sits in the bed so the seeds that want drier only the bottom 1/2 cm gets wet while the seeds that don't mind wet could sit lower and the bottom 1/2 of the tray would get wet.  Stuff like lettuce will germinate in waterlogged conditions while I think spinach wants a bit more drying.  Of course spinach can be challenging to get to germinate well in hydroponic situations.

[TCLynx]

onion seeds I have started liked it pretty wet.

[Kobus Jooste]

Here is what I have tried.  The mix is 60% fine gravel 40% coconut husk.  The mix goes into polystyrene 12 plant trays, and if it works, the seedlings will stay here until transplant into the grow beds.  The seedling starter bed is the old duckweed "snack box".  It is filled with gravel until the overflow line.  The overflow is threaded, and fitted with a threaded pipe full of holes.  The idea is that I should be able to adjust the height to which the water rises adequately with this, to have some control over the wicking process.  So far, the mix gets soaked right through pretty fast, thus I may have to reduce the height to which water rises in the bed.  Still, with the open structure of the media, I may just get away with it.  I planted lettuce, carrots, brown and Welsh onions as a first trial today.

 

 

 

[TCLynx]

Well that's pretty cool.  The poly styrene will float up I expect so shouldn't get too waterlogged with the time between watering to drain.

[Kobus Jooste]

TcLynx - the gravel actually weights it down not to allow any floating with the amount that the water rises - eventually it will likely float but not the +- 1 cm that I allow it to rise now.  Thanks for the compliment.  Lets hope it works

[TCLynx]

Ok, Anyway, hope it works well.

[Chris Smith]

I use small rock for germination. I have found that small (1/8-1/4)rock will have a wicking capacity. When using a 2"net pot filled with small rock and sitting in 1/8 of water there is usually enough wicking to keep a seed on top moist. I have found this to be a huge benefit because I cannot water log anything. The seed gets all the moisture it needs and when the roots pop they will get all the O2 they need. I get a very good germ rate this way.

In my case I am using small cinder that was washed out of my GB media. I have played with other small rock and it works similar. This technique works so well that I now germ 90% of my seeds this way. I seed net pots that directly in 2x2 foam sheets with 60 spaces. I give them a 3 day germ in the shade then float them in a sprouting table with 1 inch of water.

Here is more details on my technique.