Choosing an Appropriate Size Container

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. It's not uncommon for me, after a repot/root-pruning to pot in containers as small as 1/5 the size as that which the plant had been growing in prior to the work.

Plants grown in ‘slow’ (slow-draining/water-retentive) soils need to be grown in containers with smaller soil volumes so that the plant can use water quickly, allowing 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 why the oft repeated advice to ‘resist potting up more than one pot size at a time’, only applies when using heavy, water-retentive soils. Those using well-aerated soils are not bound by the same restrictions. As the ht and volume of the perched water table are reduced, the potential for negative effects associated with over-potting are diminished in a direct relationship with the reduction - up to the point at which the soil holds no (or an insignificant amount) of perched water and over-potting pretty much becomes a non-issue.

"I'm still thinking getting it back to the nursery so they change the pot to a smaller (and perhaps more decorative) one. I have a cactus/succulent soil - should I also tell them to repot it with this soil, or leave it with the same soil?" Your dracaena would appreciate being treated more like a succulent (like, say a jade or aeonium) in terms of soil choice and moisture management. It doesn't like any part of the soil being fully saturated, and it doesn't like media that support long intervals between waterings. There are several things you can do to minimize the amount of excess water a planting CAN hold, either passively or actively, ask if you have interest. Using wicks to drain the soil or ballast to limit how much excess water the soil can hold is another trick that puts simple physics to work. In all honesty, I think it puts you at a disadvantage if you allow someone else to decide what's appropriate when they've already shown they lack the experience to get it right.

Another question about light (this is a general question for all house plants) - the plant is getting light (not direct) from a north & east window (see picture below). Let's assume the light is not enough - will the plant benefit if I place it in the balcony for 3 days of the week so it gets much more light in these 3 days? Is this a good/bad practice? Generally speaking, it would be a good practice, however, if the difference in light levels is significant enough, it could result in unintended consequences. If you ask the leaves to tolerate light levels beyond what they are capable of adjusting to, it can start a shedding process (resorption and abscission) that is irreversible. At the heart of the issue is the reduction in the flow of a growth regulator (auxin) through the abscission zone where leaves attach to the stem/crown. Polar (toward the roots) flow of a minimal amount of auxin through that zone is required to prevent an abscission layer from forming, which compartmentalizes the leaf and causes it to be shed. Something I wrote about leaves' a ability to adapt:

Light Acclimation in Leaves

The degree to which a leaf can 'acclimate' to changes in photo load is limited. IOW, you can't expect a leaf that emerged under a full sun light load to acclimate to light levels in a dim corner, any more than you can expect a leaf that emerged in a dim corner to acclimate to a full sun site; this, no matter how long you allow for acclimation. Too, the plant's ability to adapt to higher light loads is greater than its ability to adapt to lesser light loads.

Generalizing, and using a 1-10 numerical example (1 is low, 10 is high light) to illustrate: If a leaf emerges where the light level is measured at 5 units, it's range of adjustment might only be 3.5 on the low side, but 8 to 8.5 on the high side.

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Ideally, it would be a significant benefit if you site the plant indoors in a very bright location with maybe some morning/east direct sun, and move the plant outdoors into full, or best, open shade.

Al