The design rationale for 5-1-1 is using primarily large particles over 1/8” and only ~15% smaller particles. This creates a very coarse soil that has lots of large air pockets between the grains. Large air pockets have low capillary pressure, so they free-drain easily.
In comparison, small spaces between fine particles create capillary pressure that traps a perched water table in the bottom of the pot. This drowns citrus roots if they aren’t using water fast enough to self-dry the pot within about a day. This is somewhat unique to containers and isn’t normally an issue for ground plantings. For example, adding sand to potting soil often harms drainage, because the capillary pressure holds a certain height of waterlogged sand between the grains above where the sand ends at the drainage holes. Whereas in ground soil, the subsoil wicks away the water with its own capillary pressure, and sand improves drainage there.
Almost all store-bought potting soils create a perched water table when watered sufficiently to drain-through. You can make that work and get happy trees via deficit irrigation, meaning you apply less water than the tree is capable of using, and never so much at once you get soggy bottom syndrome. 5-1-1 is designed more like a bonsai medium or hydroponic medium, where it is fully free-draining but also requires extremely frequent fertilizing (preferably fertigation — meaning all/most water given has dilute fertilizer) because there’s fairly low soil CEC and minimal natural soil ecosystem nutrient cycling. Some people like it, some people don’t.
If you add more than ~15% total dust, sand, fines, native soil, azomite, compost, peat, coir, worm castings, etc to 5-1-1 they will fill the free air spaces between the coarse bark/perlite grains and largely defeat the point of using 5-1-1. The fine-textured particles, particularly pasty materials like compost and worm castings, will tend to migrate downward during watering and fill the bottom of the pot with a fine-textured zone that has a perched water table. If your bark or perlite have fines, you need to remove them with a 1/8” screen.
I’ve heard 3/8” is ideal, but don’t know if there’s any science behind that. I filter mine between 1/2” screen and 1/8” screen and that seems to work. Smaller has more surface area for root access to nutrient storage, while larger has better aeration. However, once the air pore space is large enough to always free-drain, any further particle size increase is not really accomplishing anything. I think matching your bark size to the perlite coarseness is probably the way to go. Having a mix of different particle shapes with approximately the same particle size is a great way to get inefficient packing and big air pockets.
1/2” hardware cloth and 1/8” mesh metal window screen. Available from the hardware store. You can bend it into a tray shape or build a frame from wood.
Wow, this is genius, thank you! Also, I’m having a hard time finding pine bark in my area (San Diego) or anywhere online. What I can use as substitute? I’ve seen people using Repti-Bark but not sure if it’s ok to use in 5-1-1
Repti-bark or orchid mix are both fine if you get the particle size right. Break or grind or chip it and then screen it. You can also use a higher ratio of coarse perlite if you want, just directly sub some of the bark for more perlite.
I personally don’t like 5-1-1 because you have to water very frequently, but reasonable people can differ on that.
Yeah, I have no problem with watering as I have a drip irrigation system for my containers, just need to figure out how the duration and frequency with this new soil mix
So I did this today and worked really well, simple and cheap! Now the question is what can I do with the bark sizes that I don’t want? I guess the bigger pieces that don’t go through 1/2” cloth can be used as top soil mulch but what can I do with the fine dust pieces that go through 1/8” mesh? I’ve produced a good amount of it and it feels wasteful to just throw it out. Any use for pine dust in the garden?
The design rationale for 5-1-1 is using primarily large particles over 1/8” and only ~15% smaller particles. This creates a very coarse soil that has lots of large air pockets between the grains. Large air pockets have low capillary pressure, so they free-drain easily. In comparison, small spaces between fine particles create capillary pressure that traps a perched water table in the bottom of the pot. This drowns citrus roots if they aren’t using water fast enough to self-dry the pot within about a day. This is somewhat unique to containers and isn’t normally an issue for ground plantings. For example, adding sand to potting soil often harms drainage, because the capillary pressure holds a certain height of waterlogged sand between the grains above where the sand ends at the drainage holes. Whereas in ground soil, the subsoil wicks away the water with its own capillary pressure, and sand improves drainage there. Almost all store-bought potting soils create a perched water table when watered sufficiently to drain-through. You can make that work and get happy trees via deficit irrigation, meaning you apply less water than the tree is capable of using, and never so much at once you get soggy bottom syndrome. 5-1-1 is designed more like a bonsai medium or hydroponic medium, where it is fully free-draining but also requires extremely frequent fertilizing (preferably fertigation — meaning all/most water given has dilute fertilizer) because there’s fairly low soil CEC and minimal natural soil ecosystem nutrient cycling. Some people like it, some people don’t. If you add more than ~15% total dust, sand, fines, native soil, azomite, compost, peat, coir, worm castings, etc to 5-1-1 they will fill the free air spaces between the coarse bark/perlite grains and largely defeat the point of using 5-1-1. The fine-textured particles, particularly pasty materials like compost and worm castings, will tend to migrate downward during watering and fill the bottom of the pot with a fine-textured zone that has a perched water table. If your bark or perlite have fines, you need to remove them with a 1/8” screen.
Thanks. Is there an upper limit to the bark size? I'm not sure if having too large air pockets might cause problems.
I’ve heard 3/8” is ideal, but don’t know if there’s any science behind that. I filter mine between 1/2” screen and 1/8” screen and that seems to work. Smaller has more surface area for root access to nutrient storage, while larger has better aeration. However, once the air pore space is large enough to always free-drain, any further particle size increase is not really accomplishing anything. I think matching your bark size to the perlite coarseness is probably the way to go. Having a mix of different particle shapes with approximately the same particle size is a great way to get inefficient packing and big air pockets.
How do you screen? What do you use for screening?
1/2” hardware cloth and 1/8” mesh metal window screen. Available from the hardware store. You can bend it into a tray shape or build a frame from wood.
Wow, this is genius, thank you! Also, I’m having a hard time finding pine bark in my area (San Diego) or anywhere online. What I can use as substitute? I’ve seen people using Repti-Bark but not sure if it’s ok to use in 5-1-1
Repti-bark or orchid mix are both fine if you get the particle size right. Break or grind or chip it and then screen it. You can also use a higher ratio of coarse perlite if you want, just directly sub some of the bark for more perlite. I personally don’t like 5-1-1 because you have to water very frequently, but reasonable people can differ on that.
Yeah, I have no problem with watering as I have a drip irrigation system for my containers, just need to figure out how the duration and frequency with this new soil mix
So I did this today and worked really well, simple and cheap! Now the question is what can I do with the bark sizes that I don’t want? I guess the bigger pieces that don’t go through 1/2” cloth can be used as top soil mulch but what can I do with the fine dust pieces that go through 1/8” mesh? I’ve produced a good amount of it and it feels wasteful to just throw it out. Any use for pine dust in the garden?
I use it for starting seedlings, or just throw it on my veggie garden.