Rockwool in Pots and Planters

cottagegardenlover(9b)June 22, 2013

The more I research the more I'm sold that rockwool would probably be best for my situation.

I have an extensive outdoor container garden with roses, boxwood topiaries, clematis and other perrenials, plus I want to grow camellia's and lemon trees indoors. I have a disability where I can only do a little work at a time and not very strenuous. I have caregivers help me.

I just haven't been able to talk to anyone who uses rockwool in your average container garden. All the online posts are from marijuana sites for use in a hydroponic system. I realize it's hydroponics, but I'm wondering if anyone else out there has used it for outdoor plants and houseplants?

I'm also wondering if it would work well, at least indoors with wick watering from below in the saucer?

Plus, they talk about measuring the Ph of your tap water, and I'm wondering if this is necessary after the initial prep work to bring the Ph down before planting. I've seen Al post that Ph is not important because it will be naturally volatile.

Has anyone rootpruned their plants grown in rockwool? I imagine that it shouldn't be any more difficult than rootpruning my boxwood trees, and we cut off the outer 2 inches of the rootball in a circular motion. Then putting it back in the container with new or reused clean rockwool around it.

I think it will be the best option for me because it is so lightweight that my helpers and I can manage it plus it won't involve a lot of mixing large quantities of rocks etc. It holds moisture for a long time so I won't have to water as frequently, but still allows for air.

Can anyone tell me if I would get a perched water table (PWT) when using only rockwool in a container?

I plan to add some Physan 20 to control algae when I fertigate with Foliage Pro and Protekt. Plus I will mulch with a layer of decorative pea gravel on top to keep the light out.

Does anyone have any suggestions or personal experiences with this medium to share with me?


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nil13(z21 L.A., CA (Mt. Washington))

You know my opinion of rockwool. I can't stand the stuff.

    Bookmark   June 22, 2013 at 11:04AM
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C...without knowing all the properties of rockwool...I would say it is a poor choice for containers. The properties we want in a container mix is: drainability and the ability to perch some water without being too dense (fine particles). This is why perlite (for example) is so widely used. It is a volcanic rock that is heated to the point it explodes like popcorn. It is lightweight and has many finite holes for water and nutrients to be used by roots.

    Bookmark   June 22, 2013 at 4:48PM
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Okay, so Nil, why do you hate it so much?

Fire, I've just been reading up and watching the videos on the Grodan site. It states:
"Grodan Rockwool, when allowed to drain by gravitational pull, i.e. at field capacity contains 80% solution, 15% air pore space and 5% Rockwool fibers. This ratio of solution to air promotes vigorous root growth. Plants growing on Rockwool will remove solution and increase the ration of air-pore space to solution. Thus, if a higher proportion of air is desired in the root zone increasing the time between watering will increase the percent of air.

The tension required to remove solution from Rockwool increases only slightly as Rockwool dries. This means that it is as easy for a plant to remove solution from saturated Rockwool as it is from Rockwool that has given up 50% or even 70% of its moisture. Thus, plants grown in Rockwool are not exposed to water stress until the Rockwool is almost completely dry. Given that a standard Rockwool slab used for tomato production holds 15 liters of water, the grower has tremendous flexibility with regard to watering and control over the air content of the root zone. "

If I were able bodied I would gladly put in the time and effort to make Al's gritty mix and enjoy the project; but it's just not an option for me because of my disability.

Rockwool is extremely lightweight for me and my caregivers to transport, won't need all the manual labor and doesn't need to be repotted for a long time.

But I'm still wondering if I would get a perched water table (PWT) ? I'm thinking not because it absorbs like a sponge and drains off the rest.

Thanks for your input! I'm open to any feedback. I know I have to weigh all the pros and cons and give consideration to my special circumstances. :)

I'll probably try a couple plants to see what it's like.

Lucy :)

    Bookmark   June 23, 2013 at 9:25AM
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Lucy, This sounds very interesting...

    Bookmark   June 23, 2013 at 10:28AM
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nil13(z21 L.A., CA (Mt. Washington))

My experience is that it holds too much water, it's not reusable, it's like working with fiberglass insulation with protective gear required, removing the medium for repots destroys too many feeder roots, and it doesn't have enough mass to keep plants stable.

    Bookmark   June 23, 2013 at 11:34AM
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nil13(z21 L.A., CA (Mt. Washington))

oh and those big chunks make it difficult during repoting to get the medium to settle around the roots by shaking.

    Bookmark   June 23, 2013 at 11:50AM
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I see,

Thanks for the input Nils. I really appreciate your feedback.

There are definitely some disadvantages. Learning the correct amount of water with it will be a challenge I believe. I can wear gloves when handling it.

I think I'll have to try out a pot and see if the pros outweigh the cons for my unusual circumstances.

As I said, the alternatives have many attractions, but with my particular case the cons may outweigh the pros.

I'll let you know how it goes.

Lucy :)

    Bookmark   June 23, 2013 at 7:05PM
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nil13(z21 L.A., CA (Mt. Washington))

It sounds like you need to experiment a bit.

    Bookmark   June 24, 2013 at 10:54AM
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