Gritty mix for indoor plants - good or bad plan?

RainbowThumbApril 7, 2014

I think I joined this forum back in 2005 or 2006, but after coming back to read some more, my searches all led me back to the Gritty Mix topic. Wish this stuff was here several years ago, or at least that it was as popular back then.

I used to have a Song of India Dracaena that eventually died. And a Sansevieria too. Yes, it is possible to kill a snake plant. My wife overwatered it in an undrained container and by the time I realized what had happened it was too late.

Rather than try to replace these plants, I decided to wait because I knew we wanted to sell this house and move into a larger one. The sun-facing windows in this older house get colder in the winter, and everything else told me "just wait." We will be closing on our new home a week from tomorrow and moving in about 11 days.

So yesterday I started doing some research in order to plan for replacing my song of india that I liked so much, possibly getting more. Snake plant(s) too. I also think I want to get one or two spider plants for hanging, some palms, and possibly ferns. I have a feeling I will need to order at least some of these online in order to get what I'm looking for. And because I don't want to pay out of my butt for plants, I will probably be ordering smaller ones (2 - 4 inch containers) and just growing them myself. Because of this, I naturally want the plants to grow as fast as possible.

This led me to questions about containers, mainly, container sizing. I have 2 fairly large decorative containers that I would like to reuse -- these are what my original Sansevieria and Dracanea were potted in. They are decorative, sit right on the floor, and have zero drainage. So I think what I am going to do is pot-in-pot -- use drained terracotta pots for the plants themselves, and simply place these pots within the decorative containers. But because the decorative containers are so large, there will need to be some kind of pedestal for them to sit on inside (such as another upside-down terracotta container). The pedestal will be dual-purpose: firstly, to allow water to drain down out of the plant root container, and secondly, to elevate the root container to the top of the decorative container. And I have a lot of range when deciding how large of a pot / how large of a pedestal to use. So I started googling for "pitfalls of choosing too large of a container", and found Al Tapla's posts.

So I am going to try out the 1:1:1 gritty mix, that seems like a no-brainer after reading the excellent literature he posted here about it. My questions are not so much how to structure the soil now, but how to structure the assembly within my decorative containers. I know the inner pot will have a drain hole, I believe that Garden Ridge in my area sells the ones that have a single drain hole in the bottom center, which leads to my first question: Should I drill additional holes around the circumference of the terracotta container? Or will that not be necessary to improve drainage and lower the PWT? I don't want to damage the terracotta containers, so if they should not be drilled, please let me know.

Second question has to do with convenience. After I assemble the structure within the decorative container, I don't want to have to disassemble it until it is time to repot. I just want to water in-place. I think this should be feasible because, as long as I set up the bottom pedestal correctly, I should be able to hear water dripping out of the top container and landing on the bottom of the decorative container. That is how I plan to know when I've watered enough, and should stop / move on to the next plant. Will this cause any issues I am not foreseeing? I definitely don't want water to pool at the bottom, and these plants will all be indoors, so I am unsure of evaporation speed. Would I be better off having a small layer of lava rocks at the bottom of the decorative container to absorb the water? Or will it not matter?

My third question has to do with how to fill in the gap between the outer walls of the inner pot / pedestal and the inner walls of the decorative container. I don't want the whole assembly to be heavier than it needs to be, but I also know I want something in place to buffer the void and minimize movement of the inner pots within the decorative container. For this I have an idea of using the byproducts of my paper shredder (shredded paper). Of course I don't want it to look goofy, so I am thinking that I would probably use shredded paper or some other lightweight filler packed tightly inside (peanuts maybe), and then a decorative filler for just the top. Any ideas on this? Perhaps smooth stones, pea gravel, lava rock, or something else? I know I will be spilling some water over this and that the filler underneath will get wet, so I want to make sure I am not doing something I shouldn't.

I am leaning toward purchasing as large a terracotta pot that will fit the diameter of the decorative container -- perhaps up to 3 gallons, maybe more, I am not sure as I haven't measured anything or shopped this yet. I am still in the idea forming phase. Based on what I've read from Al, this should be okay with the gritty mix. I am sure a lot of the water will be wasted at first with a smaller root system, but it also seems like this would be the best approach for uninhibited root growth for younger plants. If I can find a good fit, it should also minimize the need for a decorative "mulch" at the surface, to hide the fact that there are actually 2 concentric circular containers in the whole assembly.

Any other ideas, or things I should watch out for?

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

I have plants in gritty growing in a "pot in a pot" in my house. You are spot on about hearing the water trickle out while watering. My pots are ceramic and plastic. The plastic pot fits tightly leaving a reservoir at the bottom. The roots evetually grow down into that moist void space.

Now about the water in the bottom. If the pots are glazed ceramic, the water won't evaporate very fast. Any raw ceramic, like on the very bottom, will help evaporate out the water. It will also destroy a hardwood floor because of the moisture, so lift it off the ground if the bottom is not glazed. You are going to need to figure out a way to remove the water in the bottom of the pot. With my small ones, I just take them outside and tip them on their sides to dump the water. This would be problematic with a large heavy container. A downtube that you could stick a siphon in would work.

The interior stand could be another pot. Generally, I find that to be a bad idea. Sometimes it works and is the right height, but not usually. I make a stand out of 3/4" PVC at the exact right height. This leaves the bottom with as much open space as possible and therefore the greatest capacity for water. You want that void to be empty, no lava rock or anything. That just takes up space unnecessarily.

Don't use paper to fill voids. This will be a humid environment and the paper will get funky. Long strand sphagnum moss works well. It also works well as a mulch so that you don't see two pots. If you need to take up a considerable amount of space between the two pots, cut pieces of Styrofoam insulation board and glue them to one of the pots. You don't want stuff falling down into the void if you have remove the interior pot. Just use a couple dabs of window caulk. It can be a good idea to size the interior pot small enough to be able to get a 1/2" pvc stand tube in there between the two pots. This will allow you to stick a smaller tube in there to siphon out the water.

You don't need to drill additional holes in a terra cotta pot.

    Bookmark   April 8, 2014 at 11:31AM
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