Rock Wool

[hooksbob]

I've seen various posts on rock wool, with conflicting information. Consensus sems to be soaking in a low ph solution overnight. I've soaked mine in tap water overnight currently. Do I need to adjust the ph and do this again? How do I adjust the ph of the water naturally?

[rfeiller]

the build up of organics in the water will lower the pH, that takes time. your pH should be around 7.3 or so out of the tap, isn't it? if you want to accelerate it naturally use peat in a sack it wil lower it naturally, it does tint the water. the best way to determine what you need to do is get a gallon of distilled water and soak one (depending on size of block small 2x2 or less i would put several in the water) of the mineral wool blocks in it overnight with aeration. check pH in morning.

the mineral wool 6x6 blocks i used were pH neutral. depends on the mfg. coir is another one that you have to test some is pH neutral and some quite alkaline.

[urbanfarmer]

You need to soak it in something with a pH of 5.0 - 5.5 because it has a build up of lime from the manufacturing process. This goes for all rock wool or it's not rock wool. If you leave it there, it will cause the root zone to be very basic thereby creating what's called nutrient lockout for your plant. If you are not using the rock wool as a medium and are just starting the seed in it and transplanting to a gravel grow bed for instance, it won't have much of an impact because the roots will come waaaay out of the cube.

[davidstcldfl]

Hi hooksbob....sometime back I tried a slab of rockwool cubes from the hydro store. The directions said to pre-treat for the high PH by adding some lemon juice to water and soaking them in it 1st, before using. They gave the target range of 5.5 ph.
Of course, I did the 'guy thing' and tried using them without reading the directions. Nothing sprouted and I still have about a half of a slab that I didn't use.

I now use oasis horti-cubes, with great success. I just drop the seed in and add water....no pre-treating. Doesn't get easier then that.
http://www.hydro-gardens.com/germinate.htm#oasiscubes

[urbanfarmer]

Ya, I'm not a fan of rockwool either. Those oasis cubes are pretty popular. I still have about 3000 rockwool cubes left. I find the peat pellets from walmart so much easier to play with. The cheapest option is taking some worm poop or even some fine sifted fertilizer and mold it into a cube or ball and plant your seed in that. Works pretty darn good, and you can just put it in the gravel grow bed.

[rfeiller]

Rock wool I like for cuttings and larger plants for flood and drain or with a mat. For seeds jiffy pellets, I like the containment nets they have.

[hooksbob]

Thanks all. I soaked the cubes overnight, and planted the seeds. They seem to be doing well. I'm going to place them directly in my ebb and flow bed, with hydroton. When should I place them in the bed?

[cedarswamp]

I vote for now, at least that's how I do it if I'm using Grodans. Which isn't that often anymore, I've started to prefer direct seeding to the GB.