Repotting and Pot Size Questions

uniquelydivine(6)September 1, 2012

I'm going to repot about 7 plants and wanted some advice on what size pots to get.

They have really outgrown the nursery pots. Some have roots coming out the bottom and some are tilting over. Most are 6 inch plants. I have two pothos rooting in water and the vases have alot of roots.

I went to Home Depot and got some pots but I'm not sure if they are too big or too small.

Should I use this 8-3/4 pot to repot the plants:

Or should I use the same 6 inch:

Please note that the next size up from the 6 inch is the 8-3/4.

I also wanted to know if I put wire mesh in the bottom of the pot if that would be OK to prevent the soil from running out the bottom.

Thanks everyone!

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tapla (mid-MI z5b-6a)

Growing and what you're taught or what you learn about growing is better if you take a holistic perspective. I think it's predictable that this question will garner suggestions based on the assumption that the soil you're using is flawed; and indeed, the need to be concerned about pot size and how large a pot you move your plants to when you pot up is intrinsic to the use of only SOME soils, not ALL soils.

This is something I wrote a while ago about pot sixes and soil choices:

How large a container "can" or "should" be, depends on the relationship between the mass of the plant material you are working with and your choice of soil. We often concern ourselves with "over-potting" (using a container that is too large), but "over-potting" is a term that arises from a lack of a basic understanding about the relationship we will look at, which logically determines appropriate container size.

It's often parroted that you should only move up one container size when "potting-up". The reasoning is, that when potting up to a container more than 'one size' larger, the soil will remain wet too long and cause root rot issues, but it is the size/mass of the plant material you are working with, and the physical properties of the soil you choose that determines both the upper & lower limits of appropriate container size - not a formulaic upward progression of container sizes. In many cases, after root pruning a plant, it may even be appropriate to step down a container size or two, but as you will see, that also depends on the physical properties of the soil you choose.

Plants grown in "slow" (slow-draining/water-retentive) soils need to be grown in containers with smaller soil volumes so the plant can use water quickly, which allows air to return to the soil before root issues beyond impaired root function/metabolism become a limiting factor. We know that the anaerobic (airless) conditions that accompany soggy soils quickly kill fine roots and impair root function/metabolism. We also know smaller soil volumes and the root constriction that accompany them cause plants to both extend branches and gain o/a mass much more slowly - a bane if rapid growth is the goal - a boon if growth restriction and a compact plant are what you have your sights set on.

Conversely, rampant growth can be had by growing in very large containers and in very fast soils where frequent watering and fertilizing is required - so it's not that plants rebel at being potted into very large containers per se, but rather, they rebel at being potted into very large containers with a soil that is too slow and water-retentive. This is a key point.

We know that there is an inverse relationship between soil particle size and the height of the perched water table (PWT) in containers. As particle size increases, the height of the PWT decreases, until at about a particle size of just under 1/8 inch, soils will no longer hold perched water. If there is no perched water, the soil is ALWAYS well aerated, even when the soil is at container capacity (fully saturated).

So, if you aim for a soil (like the gritty mix) composed primarily of particles larger than 1/16", there is no upper limit to container size, other than what you can practically manage. The lower size limit will be determined by the soil volume's ability to allow room for roots to 'run' and to furnish water enough to sustain the plant between irrigations. Bearing heavily on this ability is the ratio of fine roots to coarse roots. It takes a minimum amount of fine rootage to support the canopy under high water demand. If the container is full of large roots, there may not be room for a sufficient volume of the fine roots that do all the water/nutrient delivery work and the coarse roots, too. You can grow a very large plant in a very small container if the roots have been well managed and the lion's share of the rootage is fine. You can also grow very small plants, even seedlings, in very large containers if the soil is fast (free-draining and well-aerated) enough that the soil holds no, or very little perched water.

I have just offered clear illustration that the oft repeated advice to "only pot up one size at a time", only applies when using heavy, water-retentive soils. Those using well-aerated soils are not bound by the same restrictions.

Also, there is a considerable difference in the impact on plant vitality, especially over the long term, between simply potting up and repotting. Repotting, which includes a change of soil and root pruning, ensures at least the opportunity for the plant to return to growing at as close to its genetic potential as possible, where only potting up ensures the plant can never grow to its potential because potting up is in itself, limiting.


    Bookmark   September 1, 2012 at 12:39PM
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pirate_girl(Zone7 NYC)

I'm sorry, I don't mean to be difficult, it's really hard to say w/out seeing the plants.

Also, those seem rather deep, or maybe that's an illusion? Do those saucers come off? If not, I wouldn't use them.

Pothos are good potted tight, like 3 cuttings per 3" Pot, that's been my experience starting them off. Their roots can be trimmed to fit the pot, doesn't hurt the plant at all.

You can, but needn't put screen on the bottom, you can just use a couple of layers of newspaper. Trace the outline of the bottom of the pot on a newspapers several pages thick at least. Cut it out & place inside the pot to line it, doesn't matter when it gets wet, it'll dry & the soil stays in, I've been doing this for years. Some folks use paper towels or even coffee filters for the same purpose.

    Bookmark   September 1, 2012 at 12:45PM
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@ pirate_girl

The bottom of the pots come off. They are as deep as clay saucers (same height/depth). I already bought the screen (wish I saw your post before I bought it). The bottom (saucer) is detachable, meaning once I water I would have to pull it out to empty the water. Would the screen still be a good idea? Thanks.

    Bookmark   September 1, 2012 at 1:57PM
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pirate_girl(Zone7 NYC)

It's good the saucers come off. Thought I cleared up the screen question above, but no, I wouldn't bother w/ the screen, just the newspaper.

    Bookmark   September 1, 2012 at 2:11PM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

Uniquely, I have a lot of pots like that and it's crucial to not let water sit in the saucers. I take them off for the summer while plants are outside. I use them inside, but don't snap them on tight. Then I can take plants to tub or sink to water and if they're still a bit drippy when I put them back, (although I try to wait an hour or 2,) the saucer catches the drips.

The one mistake I think people make when first putting a plant in a much bigger pot is thoroughly soaking all of the soil. It's counter-intuitive because the "soak thoroughly, then let dry before watering again" mantra is ubiquitous, and rightly so since that's the best thing to do. EXCEPT, IMO, in this situation. Slowly moisten the root ball area and try to let the bulk of the rest of the soil remain fairly dry. I often do this with a spray bottle to make sure the water isn't flowing instead of deeply moistening. This allows you to keep the small root ball in the middle of the pot moist as needed while the roots grow into the surrounding soil. As they do, you can moisten more and more of the soil. After about a month, I do the first thorough soaking until there's lots of drainage. Then the plant should be ready for normal treatment. When I restrain watering like this at first, newly potted babies do so much better. If the soil at the bottom of the pot never gets water-logged, it can't stay soggy. I like to put them in much bigger pots too, so they don't blow around.

    Bookmark   September 1, 2012 at 3:13PM
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dellis326 (Danny)

Use the screen is you have it, it will not do any harm.

It is unnecessary with a fast draining soil mix but if it make you feel better go ahead.

I prefer a wider, shallower pot then tall pot shape and I would always use what many would consider too big if I had the space. Some plants do fine tight but most will do better with space to grow. More often than not, it is deep, closed in, fine soils that cause problems.

    Bookmark   September 1, 2012 at 8:45PM
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tapla (mid-MI z5b-6a)

To expand on the above - Deeper pots are actually easier to grow in, but only if you're using a soil that supports a notable volume of perched water. Soils like MG and MGMC usually support from 3-6+" of perched water at container capacity (when the soil has been fully saturated & has just stopped draining). If for conversational purposes we say that a soil supports 4" of perched water, in a 6" deep container 2/3 of the soil is completely saturated, and in a 4" deep container 100% of the soil will be completely saturated at container capacity. When this saturation occurs, root function can be seriously affected, or worse, root rot can get a foothold very easily. In a 12" deep container, the same soil would only have 1/3 of the soil volume saturated at container capacity, which is why it's easier to grow in deeper containers.

When using soils that support little or no perched water, it doesn't matter how deep the container is or how large the volume of soil. You can't over-pot because it's only the volume of perched water a water-retentive soil contains that makes over-potting such a bugaboo.

That isn't to say that simply growing in a deep container cures all soil ills. There are still the issues of reduced O2 volumes in soils that support significant amounts of perched water, and the noxious gases (sulfurous compounds, methane, CO2 ....) that are produced in the anaerobic conditions that prevail at the pot bottom to consider when using water-retentive soils.

There are 2 perspectives to look at when we say some plants like to be root bound. One perspective is the grower's, and it's more accurate to say I like to grow this plant root bound, because .....
* It keeps the plant smaller, and that's what I prefer
* It helps me deal with my water-retentive soil and allows air to return to the soil faster
* I tend to over-water, and it helps reduce the negative impact of that practice because tight roots allow air to return to the soil faster
* I think it helps increase bloom profusion in this particular plant

None of the above are from the plant's perspective. The plant simply recognizes tight roots as stress, and stress is something the plant would prefer to avoid. Stress can lead to strain, and strain if uncorrected always leads to death of the organism. Stress means the plant is operating at near the limits it was genetically programmed to deal with, and strain is the plant operating at beyond those limits - neither is a good thing from the plant's perspective, so no plant prefers to be grown with tight roots, no matter how well they seem to tolerate that condition.

Often, plants with extremely tight roots are dying, albeit slowly, we just fail to recognize the symptoms of their decline for what they are. Most of us here at GW have come to recognize the difference between potting up and repotting, but the hobby container gardening community apart from the few that we forum denizens represent, for the most part haven't a clue about how much benefit can be extracted from a simple root-pruning and repot as opposed to potting up - the difference is very significant.


Here is a link that might be useful: More about tight roots

    Bookmark   September 2, 2012 at 11:38AM
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