Pots / containers should normally use potting mix instead of regular dirt due to the tendency of the dirt to get compacted and become hard. Fabric pots are supposed to be less prone to this problem - although that doesn’t mean it can’t be a problem!
In my understanding, fertile soil (i.e., that you’d have in your garden, not in a pot) is usually more nutritious for a plant (if that’s the right way to put it) than potting soil on a per volume basis.
What I’m wondering about is using high fertility soil (with high organic content, for example) in fabric pots and adding something like mulch into the mix to help avoid compaction.
Coarse perlite will help a lot. It’s huge! I use it and add compost. I’m still experimenting on mixes. Currently I’m trying 2 parts pine bark fines, 2 parts compost, 1/2 part perlite, and 1/2 part diatomaceous earth. I used to use 1 part of each, but I think it is too much. I used to add some amendments like azomite and other rock dusts, and I do add lime and gypsum. This is my current mix for tomatoes, peppers and other vegetables. I would skip the compost and use peat for ornamentals a 3-1-1 mix of pine, peat and perlite/DE
DE absorbs 120% it’s weight in water and keeps soil moist. When dry it adds air to the mix. perlite holds no water but allows water flow through, and add air to the mix for the roots. Compost is well documented to prevent root rot. I have seen results that are unreal with compost. it makes a huge differance. I first noticed it when one pepper was a little low on soil, and it was not really growing either. All I had on hand was compost, so I top it off with some. the next couple weeks the plant exploded in growth. From then on I add it, and found many professional growers that do too.
Here is a user from tomatoville who uses 60% MG potting mix (no moisture control, mix not potting soil, potting mix!) and 40% compost for his peppers.
Jalapeno on the left and Sweet Banana on the right
I really jam the soil down when installing trees in inground fabric pots and never suffer from it- but these are inground so roots can also reach the looser soil outside the “pots”.
Soil simply contains more substance in less space as do all things that are heavier than things lighter by volume. I’m sure it has much higher CEC (the ability to hold onto nutrients) than potting soil as well as greater water holding capacity. I would guess that soil takes half the volume as potting mix to sustain the same amount of plant, but I bet there are more reliable guidelines on the subject if you search.
Alan, to what extent do the tree roots penetrate the fabric pots?
I have this idea that some of the pots (e.g., Smart Pots) are intended to allow small roots to penetrate the fabric into surrounding soil while stopping larger roots, thus allowing the plant to pull in some nutrients from surrounding soil while limiting its ability to spread its roots outwards (which would obviously bear on the dwarfing effect of growing fruit trees in fabric pots). How well this works or doesn’t work in practice, I don’t know.
Do you have some insight into this issue that you could share?
For example, if one uses fabric pots with the intention of achieving a dwarfing effect (along the lines of fruitnut’s container-grown fruit trees), to what extent is the effectiveness of this approach affected by putting the fabric pots in the ground?
On a related subject, what kind of fabric pots do you use (I’m sure you’ve mentioned this before - it’s just that I’ve forgotten) and how long have you found them to last when buried in the ground?
I’ll let alan address the in-ground style. I’ve been using above ground containers to start trees. I’m not trying to achieve dwarfing. I’m trying to avoid circling and j-hooking roots. I’ve been using rootmaker. Their above ground bags that I’ve are lined with a fabric that traps root tips keeping them from circling or j-hooking. This encourages much more root branching upstream. I like the rootmaker plastic pots even better. They have protrusions all around them that direct roots to a hole at the end of each protrusion. The bottoms are designed to direct roots out to the holes in the lower protrusions. When a root hits the air out side the pot, it desiccates which again forces upstream branching. These create a very dense root ball with lots of root tips. Because of all the root branching, you can get quite a large tree in a fairly small pot.
I know guys that use burlap like bags. When hung, not placed on the ground, these are supposed to act like air pruning pots with root tips growing through the burlap. I’m not sure how well they work.
On to your question. I start my trees in Rootmaker Express tray 18s which prune the tap root. I generally use Promix with that. I use osomocote for a slow release fertilizer. For the micronutrients I either add Micromax or use osmocote plus which has some of the trace minerals in it.
When I transplant to the next larger container (12-16 weeks), I mix the promix with mini-pine bark nuggets. This chunkiness makes the mix even more well drained, creates lots of space in the container to accommodate the branching roots. Another thing I’ve tried is to add about 1/3 native soils. This provides some of the biotic life forms that can form a symbiotic relationship with some plants.
I believe my brand is also called Rootmaker- I do get confused because I have so many brand names of various tools of my trade circulating in my declining mind.
At any rate it is Carl Whitcomb’s second design. Both of his bag designs, which are on the market are intended to let roots escape from the pot but are girdled by the strong fabric when the root expands beyond the diameter of the very tiny holes. His original black spun fabric design has very small holes that limit the ability of roots to function outside the bag much more than his second woven green fabric design- but depending on the species somewhat.
So what are you growing that you want to use organic material? fruit trees? I guess I would handle them different as controlling nutrients seems more important with trees. Other plants you feed like everyday is Thanksgiving! Also to be clear perlite, and DE will help stop compaction. Pine bark will too, as you mentioned using mulch. I would not use hard wood, it breaks down too quick and ties up nitrogen. Pine bark is slower and works well as an amendment.
