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xerophytenyc

Let's talk Root Zone

xerophyte NYC
7 years ago

A common occurrence on this forum is problems or questions pertaining to containers and roots. The actual ingredients of a potting mix is a whole other world of information, so let's try and avoid diving in too deep into that subject matter. There is lots of good reading on substrates, such as "Al's Gritty Mix" etc.

I think we can get a healthy discussion on some other aspects of culture related to growing succulents in containers. There are always exceptions of course, but for the sake of discussion let's not get into that. Here are some important concepts and considerations, in no particular order:

  • It's critical to remember that the Earth is very different from the Container. You cannot, nor is it necessary, to duplicate the same environment that plants are exposed to in their native lands. For example:

DRAINAGE: The Earth drains better than a pot, period. A small plant growing on the side of a mountain with tons of soil below it is safe, but a small plant in a large container may not be because the pot will not drain as well.

TEMPERATURE: The Earth stabilizes soil temperatures. A plant growing in a hot 100F day in the desert has it's roots in a much cooler, safer situation than the same 100F heat and sun in a pot. The Earth has massive soil volume that resists heating up, with rocks and shrubs reflecting some heat away. A pot does not have stable root temperatures. The root zone temperatures fluctuate wildly from day to night, season to season. Hot air temps around a pot will cook the roots. The same plant is safe in the ground at even hotter temps.

A hardy plant in the wild can take sub-freezing temperatures because more likely than not, the soil is warmer than the cold air. That same cold air temperature exposure for a potted plant results in a dangerously cold root zone. Roots are fragile and die easily, putting the plant in harm's way.

SOIL VOLUME (related to drainage): In my experience, with a properly selected substrate, virtually all succulents will excel in deep and very deep pots. The more root room, the better. For some species it is mandatory. As a group, I find us succulent growers to be very good at restricting growth and creating stunted plants. If this is intentional, to achieve a "hard" look, then that's fine. But for the most part, many succulents will grow much better with more of a free root run.

WATER: In nature, succulents will often occupy specific areas, like cracks and crevices along a cliff, wedged in between rocks, shaded by other plants...The soil in these areas likely collects more moisture after rains than a nearby patch of dirt. Or heavy dews and condensation collect along crevices. The point is that along with more stable soil temperatures, native soils also have a more stable moisture content than you may think.

As growers, we are challenged with keeping the root zone consistently but barely moist, to prevent desiccation of the active root tips. There's no such thing as a watering schedule. You have to factor in all the other variables and water accordingly. You drink when you are thirsty, and that varies from day to day. We must follow our plant's cues - look for new growth, change in coloration, swelling of buds, etc. Sustain the roots.

The only time you should aim for intentional drought is during dormancy, which for most succulents is during extended colder temperatures; and for some, it's during extended heat. Even then, it could be dangerous to withhold water completely. Without a minimal moisture content, roots will die, but the top of the plant looks fine, then you water one time when you think your plant is ready only to find it turns to mush a week later. How often does that happen on this forum? A lot. It's not because you over-watered. It's because you may have previously under-watered and killed the roots, and you didn't wait long enough for the plant to generate new root tips.

MICROBIOLOGY: There's no possible way that the inherently erratic temperature and moisture fluctuation in a pot can maintain a viable microflora that resembles native soil. For that reason alone, you can avoid anything "organic". Stick with inert substrates, and chemical/ elemental fertilizers. "Organic" fertilizers rely on bacteria to unlock nutrients. I doubt very much there are good microorganisms in small containers. Peat moss and other ingredients that can decompose run the risk of turning into a toxic mess. Exercise caution.

The health of our plants can be significantly compromised without considering some of these things. The amount of light and water is of no consequence if we can't get a stable root zone.

Please feel free to comment and contribute.

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